Variadic tuple types (#39094)

* Initial implementation of variadic tuple types

* Accept new baselines

* Handle variadic elements in tuple type inference

* Special case inference between tuples with matching structure

* Restore check that rest element is last element

* Handle variadic tuples in relationship checking

* Accept new baselines

* Infer readonly constraints when inferring from readonly tuples

* Fix lint issues

* T assignable to readonly [...T] and [...T] assignable to T

* Consistent tuple normalization

* Create variadic tuple types from array literal expressions

* Accept new baselines

* Array literals have tuple types when contextual type is readonly

* Accept new baselines

* Optional elements before required elements become required elements

* Update logic for rest parameters and spread arguments

* Revert special case of contextual readonly array type

* Accept new baselines

* Fix lint issue

* Switch entirely to createTupleType based on element flags

* Don't infer readonly tuple types when inferring to variadic elements

* Handle mapped types applied to generic tuple types

* Handle constraint of indexed access type with generic tuple type

* Accept new baselines

* Address CR feedback

* Simplify indexed access types involving generic tuple types

* Propagate checkMode into getSpreadArgumentType

* Guard against missing globalArrayType

* Inference to [...T, ...U] based on implied arity of T

* Accept new baselines

* Add tests

* Emit .d.ts from tests

* Address CR feedback

src/compiler/core.ts

@@ -1201,6 +1201,14 @@ namespace ts {
         return values;
     }
 
+    export function arrayOf<T>(count: number, f: (index: number) => T): T[] {
+        const result = new Array(count);
+        for (let i = 0; i < count; i++) {
+            result[i] = f(i);
+        }
+        return result;
+    }
+
     /** Shims `Array.from`. */
     export function arrayFrom<T, U>(iterator: Iterator<T> | IterableIterator<T>, map: (t: T) => U): U[];
     export function arrayFrom<T>(iterator: Iterator<T> | IterableIterator<T>): T[];

src/compiler/diagnosticMessages.json

@@ -2414,6 +2414,26 @@
         "category": "Error",
         "code": 2617
     },
+    "Source has {0} element(s) but target requires {1}.": {
+        "category": "Error",
+        "code": 2618
+    },
+    "Source has {0} element(s) but target allows only {1}.": {
+        "category": "Error",
+        "code": 2619
+    },
+    "Target requires {0} element(s) but source may have fewer.": {
+        "category": "Error",
+        "code": 2620
+    },
+    "Target allows only {0} element(s) but source may have more.": {
+        "category": "Error",
+        "code": 2621
+    },
+    "Element at index {0} is variadic in one type but not in the other.": {
+        "category": "Error",
+        "code": 2622
+    },
 
     "Cannot augment module '{0}' with value exports because it resolves to a non-module entity.": {
         "category": "Error",

src/compiler/types.ts

@@ -5100,9 +5100,20 @@ namespace ts {
         variances?: VarianceFlags[];  // Variance of each type parameter
     }
 
+    export const enum ElementFlags {
+        Required  = 1 << 0,  // T
+        Optional  = 1 << 1,  // T?
+        Rest      = 1 << 2,  // ...T[]
+        Variadic  = 1 << 3,  // ...T
+        Variable  = Rest | Variadic,
+    }
+
     export interface TupleType extends GenericType {
+        elementFlags: readonly ElementFlags[];
         minLength: number;
+        fixedLength: number;
         hasRestElement: boolean;
+        combinedFlags: ElementFlags;
         readonly: boolean;
         labeledElementDeclarations?: readonly (NamedTupleMember | ParameterDeclaration)[];
     }
@@ -5422,6 +5433,7 @@ namespace ts {
         priority?: InferencePriority;            // Priority of current inference set
         topLevel: boolean;                       // True if all inferences are to top level occurrences
         isFixed: boolean;                        // True if inferences are fixed
+        impliedArity?: number;
     }
 
     /* @internal */

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2538,9 +2538,19 @@ declare namespace ts {
     }
     export interface GenericType extends InterfaceType, TypeReference {
     }
+    export enum ElementFlags {
+        Required = 1,
+        Optional = 2,
+        Rest = 4,
+        Variadic = 8,
+        Variable = 12
+    }
     export interface TupleType extends GenericType {
+        elementFlags: readonly ElementFlags[];
         minLength: number;
+        fixedLength: number;
         hasRestElement: boolean;
+        combinedFlags: ElementFlags;
         readonly: boolean;
         labeledElementDeclarations?: readonly (NamedTupleMember | ParameterDeclaration)[];
     }

tests/baselines/reference/api/typescript.d.ts

@@ -2538,9 +2538,19 @@ declare namespace ts {
     }
     export interface GenericType extends InterfaceType, TypeReference {
     }
+    export enum ElementFlags {
+        Required = 1,
+        Optional = 2,
+        Rest = 4,
+        Variadic = 8,
+        Variable = 12
+    }
     export interface TupleType extends GenericType {
+        elementFlags: readonly ElementFlags[];
         minLength: number;
+        fixedLength: number;
         hasRestElement: boolean;
+        combinedFlags: ElementFlags;
         readonly: boolean;
         labeledElementDeclarations?: readonly (NamedTupleMember | ParameterDeclaration)[];
     }

tests/baselines/reference/argumentExpressionContextualTyping.errors.txt

@@ -1,11 +1,11 @@
 tests/cases/conformance/expressions/contextualTyping/argumentExpressionContextualTyping.ts(16,5): error TS2345: Argument of type '(string | number | boolean)[]' is not assignable to parameter of type '[string, number, boolean]'.
-  Type '(string | number | boolean)[]' is missing the following properties from type '[string, number, boolean]': 0, 1, 2
+  Target requires 3 element(s) but source may have fewer.
 tests/cases/conformance/expressions/contextualTyping/argumentExpressionContextualTyping.ts(17,5): error TS2345: Argument of type '[string, number, true, ...(string | number | boolean)[]]' is not assignable to parameter of type '[string, number, boolean]'.
-  Types of property 'length' are incompatible.
-    Type 'number' is not assignable to type '3'.
+  Target allows only 3 element(s) but source may have more.
 tests/cases/conformance/expressions/contextualTyping/argumentExpressionContextualTyping.ts(18,5): error TS2345: Argument of type '{ x: (string | number)[]; y: { c: boolean; d: string; e: number; }; }' is not assignable to parameter of type '{ x: [any, any]; y: { c: any; d: any; e: any; }; }'.
   Types of property 'x' are incompatible.
-    Type '(string | number)[]' is missing the following properties from type '[any, any]': 0, 1
+    Type '(string | number)[]' is not assignable to type '[any, any]'.
+      Target requires 2 element(s) but source may have fewer.
 
 
 ==== tests/cases/conformance/expressions/contextualTyping/argumentExpressionContextualTyping.ts (3 errors) ====
@@ -27,14 +27,14 @@ tests/cases/conformance/expressions/contextualTyping/argumentExpressionContextua
     baz(array);                          // Error
         ~~~~~
 !!! error TS2345: Argument of type '(string | number | boolean)[]' is not assignable to parameter of type '[string, number, boolean]'.
-!!! error TS2345:   Type '(string | number | boolean)[]' is missing the following properties from type '[string, number, boolean]': 0, 1, 2
+!!! error TS2345:   Target requires 3 element(s) but source may have fewer.
     baz(["string", 1, true, ...array]);  // Error
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[string, number, true, ...(string | number | boolean)[]]' is not assignable to parameter of type '[string, number, boolean]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type 'number' is not assignable to type '3'.
+!!! error TS2345:   Target allows only 3 element(s) but source may have more.
     foo(o);                              // Error because x has an array type namely (string|number)[]
         ~
 !!! error TS2345: Argument of type '{ x: (string | number)[]; y: { c: boolean; d: string; e: number; }; }' is not assignable to parameter of type '{ x: [any, any]; y: { c: any; d: any; e: any; }; }'.
 !!! error TS2345:   Types of property 'x' are incompatible.
-!!! error TS2345:     Type '(string | number)[]' is missing the following properties from type '[any, any]': 0, 1
+!!! error TS2345:     Type '(string | number)[]' is not assignable to type '[any, any]'.
+!!! error TS2345:       Target requires 2 element(s) but source may have fewer.

tests/baselines/reference/arityAndOrderCompatibility01.errors.txt

@@ -1,21 +1,21 @@
 tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(15,12): error TS2493: Tuple type '[string, number]' of length '2' has no element at index '2'.
 tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(17,5): error TS2461: Type '{ 0: string; 1: number; length: 2; }' is not an array type.
-tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(18,5): error TS2741: Property '2' is missing in type '[string, number]' but required in type '[number, number, number]'.
+tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(18,5): error TS2322: Type '[string, number]' is not assignable to type '[number, number, number]'.
+  Source has 2 element(s) but target requires 3.
 tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(19,5): error TS2741: Property '2' is missing in type 'StrNum' but required in type '[number, number, number]'.
 tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(20,5): error TS2322: Type '{ 0: string; 1: number; length: 2; }' is not assignable to type '[number, number, number]'.
-tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(21,5): error TS2741: Property '2' is missing in type '[string, number]' but required in type '[string, number, number]'.
+tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(21,5): error TS2322: Type '[string, number]' is not assignable to type '[string, number, number]'.
+  Source has 2 element(s) but target requires 3.
 tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(22,5): error TS2741: Property '2' is missing in type 'StrNum' but required in type '[string, number, number]'.
 tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(23,5): error TS2322: Type '{ 0: string; 1: number; length: 2; }' is not assignable to type '[string, number, number]'.
 tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(24,5): error TS2322: Type '[string, number]' is not assignable to type '[number]'.
-  Types of property '0' are incompatible.
-    Type 'string' is not assignable to type 'number'.
+  Source has 2 element(s) but target allows only 1.
 tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(25,5): error TS2322: Type 'StrNum' is not assignable to type '[number]'.
   Types of property '0' are incompatible.
     Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(26,5): error TS2322: Type '{ 0: string; 1: number; length: 2; }' is not assignable to type '[number]'.
 tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(27,5): error TS2322: Type '[string, number]' is not assignable to type '[string]'.
-  Types of property 'length' are incompatible.
-    Type '2' is not assignable to type '1'.
+  Source has 2 element(s) but target allows only 1.
 tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(28,5): error TS2322: Type 'StrNum' is not assignable to type '[string]'.
   Types of property 'length' are incompatible.
     Type '2' is not assignable to type '1'.
@@ -52,7 +52,8 @@ tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(32,5): error
 !!! error TS2461: Type '{ 0: string; 1: number; length: 2; }' is not an array type.
     var j1: [number, number, number] = x;
         ~~
-!!! error TS2741: Property '2' is missing in type '[string, number]' but required in type '[number, number, number]'.
+!!! error TS2322: Type '[string, number]' is not assignable to type '[number, number, number]'.
+!!! error TS2322:   Source has 2 element(s) but target requires 3.
     var j2: [number, number, number] = y;
         ~~
 !!! error TS2741: Property '2' is missing in type 'StrNum' but required in type '[number, number, number]'.
@@ -61,7 +62,8 @@ tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(32,5): error
 !!! error TS2322: Type '{ 0: string; 1: number; length: 2; }' is not assignable to type '[number, number, number]'.
     var k1: [string, number, number] = x;
         ~~
-!!! error TS2741: Property '2' is missing in type '[string, number]' but required in type '[string, number, number]'.
+!!! error TS2322: Type '[string, number]' is not assignable to type '[string, number, number]'.
+!!! error TS2322:   Source has 2 element(s) but target requires 3.
     var k2: [string, number, number] = y;
         ~~
 !!! error TS2741: Property '2' is missing in type 'StrNum' but required in type '[string, number, number]'.
@@ -71,8 +73,7 @@ tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(32,5): error
     var l1: [number] = x;
         ~~
 !!! error TS2322: Type '[string, number]' is not assignable to type '[number]'.
-!!! error TS2322:   Types of property '0' are incompatible.
-!!! error TS2322:     Type 'string' is not assignable to type 'number'.
+!!! error TS2322:   Source has 2 element(s) but target allows only 1.
     var l2: [number] = y;
         ~~
 !!! error TS2322: Type 'StrNum' is not assignable to type '[number]'.
@@ -84,8 +85,7 @@ tests/cases/conformance/types/tuple/arityAndOrderCompatibility01.ts(32,5): error
     var m1: [string] = x;
         ~~
 !!! error TS2322: Type '[string, number]' is not assignable to type '[string]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '2' is not assignable to type '1'.
+!!! error TS2322:   Source has 2 element(s) but target allows only 1.
     var m2: [string] = y;
         ~~
 !!! error TS2322: Type 'StrNum' is not assignable to type '[string]'.

tests/baselines/reference/arrayLiteralExpressionContextualTyping.errors.txt

@@ -1,15 +1,11 @@
 tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionContextualTyping.ts(6,5): error TS2322: Type '[number, number, number, number]' is not assignable to type '[number, number, number]'.
-  Types of property 'length' are incompatible.
-    Type '4' is not assignable to type '3'.
+  Source has 4 element(s) but target allows only 3.
 tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionContextualTyping.ts(7,5): error TS2322: Type '[number, number, number, string]' is not assignable to type '[string | number, string | number, string | number]'.
-  Types of property 'length' are incompatible.
-    Type '4' is not assignable to type '3'.
+  Source has 4 element(s) but target allows only 3.
 tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionContextualTyping.ts(8,5): error TS2322: Type '[number, number, number, string]' is not assignable to type '[number, number, number]'.
-  Types of property 'length' are incompatible.
-    Type '4' is not assignable to type '3'.
+  Source has 4 element(s) but target allows only 3.
 tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionContextualTyping.ts(14,5): error TS2322: Type '[number, number, number, number, number, number]' is not assignable to type '[number, number, number]'.
-  Types of property 'length' are incompatible.
-    Type '6' is not assignable to type '3'.
+  Source has 6 element(s) but target allows only 3.
 
 
 ==== tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionContextualTyping.ts (4 errors) ====
@@ -21,18 +17,15 @@ tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionConte
     var tup: [number, number, number] = [1, 2, 3, 4];
         ~~~
 !!! error TS2322: Type '[number, number, number, number]' is not assignable to type '[number, number, number]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '4' is not assignable to type '3'.
+!!! error TS2322:   Source has 4 element(s) but target allows only 3.
     var tup1: [number|string, number|string, number|string] = [1, 2, 3, "string"];
         ~~~~
 !!! error TS2322: Type '[number, number, number, string]' is not assignable to type '[string | number, string | number, string | number]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '4' is not assignable to type '3'.
+!!! error TS2322:   Source has 4 element(s) but target allows only 3.
     var tup2: [number, number, number] = [1, 2, 3, "string"];  // Error
         ~~~~
 !!! error TS2322: Type '[number, number, number, string]' is not assignable to type '[number, number, number]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '4' is not assignable to type '3'.
+!!! error TS2322:   Source has 4 element(s) but target allows only 3.
     
     // In a contextually typed array literal expression containing one or more spread elements,
     // an element expression at index N is contextually typed by the numeric index type of the contextual type, if any.
@@ -41,6 +34,5 @@ tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionConte
     var spr2:[number, number, number] = [1, 2, 3, ...tup];  // Error
         ~~~~
 !!! error TS2322: Type '[number, number, number, number, number, number]' is not assignable to type '[number, number, number]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '6' is not assignable to type '3'.
+!!! error TS2322:   Source has 6 element(s) but target allows only 3.
     

tests/baselines/reference/arrayLiterals3.errors.txt

@@ -1,11 +1,12 @@
-tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(10,5): error TS2739: Type '[]' is missing the following properties from type '[any, any, any]': 0, 1, 2
+tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(10,5): error TS2322: Type '[]' is not assignable to type '[any, any, any]'.
+  Source has 0 element(s) but target requires 3.
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(11,38): error TS2322: Type 'string' is not assignable to type 'boolean'.
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(11,48): error TS2322: Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(11,51): error TS2322: Type 'boolean' is not assignable to type 'number'.
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(17,5): error TS2322: Type '[number, number, string, boolean]' is not assignable to type '[number, number]'.
-  Types of property 'length' are incompatible.
-    Type '4' is not assignable to type '2'.
-tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(33,5): error TS2739: Type 'number[]' is missing the following properties from type '[number, number, number]': 0, 1, 2
+  Source has 4 element(s) but target allows only 2.
+tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(33,5): error TS2322: Type 'number[]' is not assignable to type '[number, number, number]'.
+  Target requires 3 element(s) but source may have fewer.
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error TS2322: Type '(string | number)[]' is not assignable to type 'myArray'.
   The types returned by 'pop()' are incompatible between these types.
     Type 'string | number' is not assignable to type 'Number'.
@@ -24,7 +25,8 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error
     
     var a0: [any, any, any] = [];                             // Error
         ~~
-!!! error TS2739: Type '[]' is missing the following properties from type '[any, any, any]': 0, 1, 2
+!!! error TS2322: Type '[]' is not assignable to type '[any, any, any]'.
+!!! error TS2322:   Source has 0 element(s) but target requires 3.
     var a1: [boolean, string, number] = ["string", 1, true];  // Error
                                          ~~~~~~~~
 !!! error TS2322: Type 'string' is not assignable to type 'boolean'.
@@ -40,8 +42,7 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error
     var [b1, b2]: [number, number] = [1, 2, "string", true];
         ~~~~~~~~
 !!! error TS2322: Type '[number, number, string, boolean]' is not assignable to type '[number, number]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '4' is not assignable to type '2'.
+!!! error TS2322:   Source has 4 element(s) but target allows only 2.
     
     // The resulting type an array literal expression is determined as follows:
     //      - the resulting type is an array type with an element type that is the union of the types of the
@@ -59,7 +60,8 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error
     var c0: tup = [...temp2];                         // Error
     var c1: [number, number, number] = [...temp1];    // Error cannot assign number[] to [number, number, number]
         ~~
-!!! error TS2739: Type 'number[]' is missing the following properties from type '[number, number, number]': 0, 1, 2
+!!! error TS2322: Type 'number[]' is not assignable to type '[number, number, number]'.
+!!! error TS2322:   Target requires 3 element(s) but source may have fewer.
     var c2: myArray = [...temp1, ...temp];            // Error cannot assign (number|string)[] to number[]
         ~~
 !!! error TS2322: Type '(string | number)[]' is not assignable to type 'myArray'.

tests/baselines/reference/assignmentCompatBetweenTupleAndArray.errors.txt

@@ -1,7 +1,8 @@
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatBetweenTupleAndArray.ts(17,1): error TS2322: Type '[number, string]' is not assignable to type 'number[]'.
   Type 'string | number' is not assignable to type 'number'.
     Type 'string' is not assignable to type 'number'.
-tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatBetweenTupleAndArray.ts(18,1): error TS2741: Property '0' is missing in type '{}[]' but required in type '[{}]'.
+tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatBetweenTupleAndArray.ts(18,1): error TS2322: Type '{}[]' is not assignable to type '[{}]'.
+  Target requires 1 element(s) but source may have fewer.
 
 
 ==== tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatBetweenTupleAndArray.ts (2 errors) ====
@@ -28,5 +29,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 !!! error TS2322:     Type 'string' is not assignable to type 'number'.
     emptyObjTuple = emptyObjArray;
     ~~~~~~~~~~~~~
-!!! error TS2741: Property '0' is missing in type '{}[]' but required in type '[{}]'.
+!!! error TS2322: Type '{}[]' is not assignable to type '[{}]'.
+!!! error TS2322:   Target requires 1 element(s) but source may have fewer.
     

tests/baselines/reference/assignmentLHSIsValue.types

@@ -225,8 +225,8 @@ foo() = value;
 
 ([]) = value;
 >([]) = value : any
->([]) : undefined[]
->[] : undefined[]
+>([]) : []
+>[] : []
 >value : any
 
 (function baz() { }) = value;

tests/baselines/reference/assignmentRestElementWithErrorSourceType.types

@@ -4,7 +4,7 @@ var tuple: [string, number];
 
 [...c] = tupel; // intentionally misspelled
 >[...c] = tupel : any
->[...c] : undefined[]
+>[...c] : any[]
 >...c : any
 >c : any
 >tupel : any

tests/baselines/reference/callWithSpread3.errors.txt

@@ -1,17 +1,18 @@
 tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(14,10): error TS2554: Expected 2 arguments, but got 3.
 tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(15,15): error TS2554: Expected 2 arguments, but got 5.
-tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(16,15): error TS2556: Expected 2 arguments, but got 4 or more.
-tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(17,15): error TS2556: Expected 2 arguments, but got 5 or more.
-tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(18,12): error TS2556: Expected 2 arguments, but got 1 or more.
+tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(16,15): error TS2554: Expected 2 arguments, but got 5.
+tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(17,15): error TS2554: Expected 2 arguments, but got 6.
+tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(18,12): error TS2554: Expected 2 arguments, but got 3.
 tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(19,5): error TS2554: Expected 2 arguments, but got 3.
 tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(20,6): error TS2557: Expected at least 2 arguments, but got 0 or more.
 tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(21,6): error TS2345: Argument of type 'number' is not assignable to parameter of type 'string'.
 tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(22,13): error TS2557: Expected at least 2 arguments, but got 1 or more.
 tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(23,13): error TS2557: Expected at least 2 arguments, but got 2 or more.
 tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(25,7): error TS2345: Argument of type 'string' is not assignable to parameter of type 'number'.
+tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(31,13): error TS2557: Expected at least 2 arguments, but got 4 or more.
 
 
-==== tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts (11 errors) ====
+==== tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts (12 errors) ====
     declare const s2: [string, string];
     declare const s3: [string, string, string];
     declare const s2_: [string, string, ...string[]];
@@ -33,14 +34,13 @@ tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(25,7): erro
 !!! error TS2554: Expected 2 arguments, but got 5.
     fs2('a', 'b', ...s2, 'c'); // error on ...s2 and 'c'
                   ~~~~~~~~~~
-!!! error TS2556: Expected 2 arguments, but got 4 or more.
+!!! error TS2554: Expected 2 arguments, but got 5.
     fs2('a', 'b', 'c', ...s2, 'd'); // error on 'c', ...s2 and 'd'
                   ~~~~~~~~~~~~~~~
-!!! error TS2556: Expected 2 arguments, but got 5 or more.
+!!! error TS2554: Expected 2 arguments, but got 6.
     fs2(...s2, 'a'); // error on 'a'
                ~~~
-!!! error TS2556: Expected 2 arguments, but got 1 or more.
-!!! related TS6210 tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts:8:33: An argument for 'b' was not provided.
+!!! error TS2554: Expected 2 arguments, but got 3.
     fs2(...s3); // error on ...s3
         ~~~~~
 !!! error TS2554: Expected 2 arguments, but got 3.
@@ -68,6 +68,8 @@ tests/cases/conformance/expressions/functionCalls/callWithSpread3.ts(25,7): erro
     fs2_(...s2_, ...s_);
     fs2_(...s2_, ...s2_);
     fs2_(...s_, ...s2_);
+                ~~~~~~
+!!! error TS2557: Expected at least 2 arguments, but got 4 or more.
     fs2n_(...s2n_);
     fs2n_(...s2);
     // fs2n_(...s2, ...n_); // FIXME: should compile

tests/baselines/reference/castingTuple.errors.txt

@@ -1,11 +1,10 @@
 tests/cases/conformance/types/tuple/castingTuple.ts(13,23): error TS2352: Conversion of type '[number, string]' to type '[number, string, boolean]' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
-  Property '2' is missing in type '[number, string]' but required in type '[number, string, boolean]'.
+  Source has 2 element(s) but target requires 3.
 tests/cases/conformance/types/tuple/castingTuple.ts(14,15): error TS2352: Conversion of type '[number, string, boolean]' to type '[number, string]' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
-  Types of property 'length' are incompatible.
-    Type '3' is not comparable to type '2'.
+  Source has 3 element(s) but target allows only 2.
 tests/cases/conformance/types/tuple/castingTuple.ts(15,14): error TS2352: Conversion of type '[number, string]' to type '[number, string, boolean]' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
 tests/cases/conformance/types/tuple/castingTuple.ts(18,21): error TS2352: Conversion of type '[C, D]' to type '[C, D, A]' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
-  Property '2' is missing in type '[C, D]' but required in type '[C, D, A]'.
+  Source has 2 element(s) but target requires 3.
 tests/cases/conformance/types/tuple/castingTuple.ts(20,33): error TS2493: Tuple type '[C, D, A]' of length '3' has no element at index '5'.
 tests/cases/conformance/types/tuple/castingTuple.ts(30,10): error TS2352: Conversion of type '[number, string]' to type '[number, number]' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
   Type 'string' is not comparable to type 'number'.
@@ -31,12 +30,11 @@ tests/cases/conformance/types/tuple/castingTuple.ts(33,1): error TS2304: Cannot
     var numStrBoolTuple = <[number, string, boolean]>numStrTuple;
                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2352: Conversion of type '[number, string]' to type '[number, string, boolean]' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
-!!! error TS2352:   Property '2' is missing in type '[number, string]' but required in type '[number, string, boolean]'.
+!!! error TS2352:   Source has 2 element(s) but target requires 3.
     var shorter = numStrBoolTuple as [number, string]
                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2352: Conversion of type '[number, string, boolean]' to type '[number, string]' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
-!!! error TS2352:   Types of property 'length' are incompatible.
-!!! error TS2352:     Type '3' is not comparable to type '2'.
+!!! error TS2352:   Source has 3 element(s) but target allows only 2.
     var longer = numStrTuple as [number, string, boolean]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2352: Conversion of type '[number, string]' to type '[number, string, boolean]' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
@@ -45,7 +43,7 @@ tests/cases/conformance/types/tuple/castingTuple.ts(33,1): error TS2304: Cannot
     var classCDATuple = <[C, D, A]>classCDTuple;
                         ~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2352: Conversion of type '[C, D]' to type '[C, D, A]' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
-!!! error TS2352:   Property '2' is missing in type '[C, D]' but required in type '[C, D, A]'.
+!!! error TS2352:   Source has 2 element(s) but target requires 3.
     var eleFromCDA1 = classCDATuple[2]; // A
     var eleFromCDA2 = classCDATuple[5]; // C | D | A
                                     ~

tests/baselines/reference/checkJsxChildrenCanBeTupleType.errors.txt

@@ -1,8 +1,9 @@
 tests/cases/conformance/jsx/checkJsxChildrenCanBeTupleType.tsx(17,18): error TS2769: No overload matches this call.
   Overload 1 of 2, '(props: Readonly<ResizablePanelProps>): ResizablePanel', gave the following error.
     Type '{ children: [Element, Element, Element]; }' is not assignable to type 'Readonly<ResizablePanelProps>'.
-      The types of 'children.length' are incompatible between these types.
-        Type '3' is not assignable to type '2'.
+      Types of property 'children' are incompatible.
+        Type '[Element, Element, Element]' is not assignable to type '[ReactNode, ReactNode]'.
+          Source has 3 element(s) but target allows only 2.
   Overload 2 of 2, '(props: ResizablePanelProps, context?: any): ResizablePanel', gave the following error.
     Type '{ children: [Element, Element, Element]; }' is not assignable to type 'Readonly<ResizablePanelProps>'.
       Types of property 'children' are incompatible.
@@ -31,8 +32,9 @@ tests/cases/conformance/jsx/checkJsxChildrenCanBeTupleType.tsx(17,18): error TS2
 !!! error TS2769: No overload matches this call.
 !!! error TS2769:   Overload 1 of 2, '(props: Readonly<ResizablePanelProps>): ResizablePanel', gave the following error.
 !!! error TS2769:     Type '{ children: [Element, Element, Element]; }' is not assignable to type 'Readonly<ResizablePanelProps>'.
-!!! error TS2769:       The types of 'children.length' are incompatible between these types.
-!!! error TS2769:         Type '3' is not assignable to type '2'.
+!!! error TS2769:       Types of property 'children' are incompatible.
+!!! error TS2769:         Type '[Element, Element, Element]' is not assignable to type '[ReactNode, ReactNode]'.
+!!! error TS2769:           Source has 3 element(s) but target allows only 2.
 !!! error TS2769:   Overload 2 of 2, '(props: ResizablePanelProps, context?: any): ResizablePanel', gave the following error.
 !!! error TS2769:     Type '{ children: [Element, Element, Element]; }' is not assignable to type 'Readonly<ResizablePanelProps>'.
 !!! error TS2769:       Types of property 'children' are incompatible.

tests/baselines/reference/compoundAssignmentLHSIsValue.types

@@ -432,14 +432,14 @@ foo() += value;
 
 ([]) *= value;
 >([]) *= value : number
->([]) : undefined[]
->[] : undefined[]
+>([]) : []
+>[] : []
 >value : any
 
 ([]) += value;
 >([]) += value : any
->([]) : undefined[]
->[] : undefined[]
+>([]) : []
+>[] : []
 >value : any
 
 (function baz1() { }) *= value;

tests/baselines/reference/compoundExponentiationAssignmentLHSIsValue.types

@@ -244,8 +244,8 @@ foo() **= value;
 
 ([]) **= value;
 >([]) **= value : number
->([]) : undefined[]
->[] : undefined[]
+>([]) : []
+>[] : []
 >value : any
 
 (function baz1() { }) **= value;

tests/baselines/reference/contextualTypeWithTuple.errors.txt

@@ -1,18 +1,16 @@
 tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(3,5): error TS2322: Type '[number, string, boolean]' is not assignable to type '[number, string]'.
-  Types of property 'length' are incompatible.
-    Type '3' is not assignable to type '2'.
+  Source has 3 element(s) but target allows only 2.
 tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(15,1): error TS2322: Type '[number, string, boolean]' is not assignable to type '[number, string]'.
-  Types of property 'length' are incompatible.
-    Type '3' is not assignable to type '2'.
+  Source has 3 element(s) but target allows only 2.
 tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(18,17): error TS2741: Property 'a' is missing in type '{}' but required in type '{ a: string; }'.
-tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(19,1): error TS2741: Property '2' is missing in type '[number, string]' but required in type '[number, string, boolean]'.
+tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(19,1): error TS2322: Type '[number, string]' is not assignable to type '[number, string, boolean]'.
+  Source has 2 element(s) but target requires 3.
 tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(20,5): error TS2322: Type '[string, string, number]' is not assignable to type '[string, string]'.
-  Types of property 'length' are incompatible.
-    Type '3' is not assignable to type '2'.
+  Source has 3 element(s) but target allows only 2.
 tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(23,1): error TS2322: Type '[C, string | number, D]' is not assignable to type '[C, string | number]'.
-  Types of property 'length' are incompatible.
-    Type '3' is not assignable to type '2'.
-tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(24,1): error TS2741: Property '2' is missing in type '[C, string | number]' but required in type '[C, string | number, D]'.
+  Source has 3 element(s) but target allows only 2.
+tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(24,1): error TS2322: Type '[C, string | number]' is not assignable to type '[C, string | number, D]'.
+  Source has 2 element(s) but target requires 3.
 tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(25,1): error TS2322: Type '[number, string | number]' is not assignable to type '[number, string]'.
   Type 'string | number' is not assignable to type 'string'.
     Type 'number' is not assignable to type 'string'.
@@ -24,8 +22,7 @@ tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(25,1): error TS23
     var numStrTuple2: [number, string] = [5, "foo", true];
         ~~~~~~~~~~~~
 !!! error TS2322: Type '[number, string, boolean]' is not assignable to type '[number, string]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '3' is not assignable to type '2'.
+!!! error TS2322:   Source has 3 element(s) but target allows only 2.
     var numStrBoolTuple: [number, string, boolean] = [5, "foo", true];
     var objNumTuple: [{ a: string }, number] = [{ a: "world" }, 5];
     var strTupleTuple: [string, [number, {}]] = ["bar", [5, { x: 1, y: 1 }]];
@@ -40,8 +37,7 @@ tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(25,1): error TS23
     numStrTuple = numStrBoolTuple;
     ~~~~~~~~~~~
 !!! error TS2322: Type '[number, string, boolean]' is not assignable to type '[number, string]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '3' is not assignable to type '2'.
+!!! error TS2322:   Source has 3 element(s) but target allows only 2.
     
     // error
     objNumTuple = [ {}, 5];
@@ -50,22 +46,22 @@ tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts(25,1): error TS23
 !!! related TS2728 tests/cases/conformance/types/tuple/contextualTypeWithTuple.ts:5:21: 'a' is declared here.
     numStrBoolTuple = numStrTuple;
     ~~~~~~~~~~~~~~~
-!!! error TS2741: Property '2' is missing in type '[number, string]' but required in type '[number, string, boolean]'.
+!!! error TS2322: Type '[number, string]' is not assignable to type '[number, string, boolean]'.
+!!! error TS2322:   Source has 2 element(s) but target requires 3.
     var strStrTuple: [string, string] = ["foo", "bar", 5];
         ~~~~~~~~~~~
 !!! error TS2322: Type '[string, string, number]' is not assignable to type '[string, string]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '3' is not assignable to type '2'.
+!!! error TS2322:   Source has 3 element(s) but target allows only 2.
     
     unionTuple = unionTuple1;
     unionTuple = unionTuple2;
     ~~~~~~~~~~
 !!! error TS2322: Type '[C, string | number, D]' is not assignable to type '[C, string | number]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '3' is not assignable to type '2'.
+!!! error TS2322:   Source has 3 element(s) but target allows only 2.
     unionTuple2 = unionTuple;
     ~~~~~~~~~~~
-!!! error TS2741: Property '2' is missing in type '[C, string | number]' but required in type '[C, string | number, D]'.
+!!! error TS2322: Type '[C, string | number]' is not assignable to type '[C, string | number, D]'.
+!!! error TS2322:   Source has 2 element(s) but target requires 3.
     numStrTuple = unionTuple3;
     ~~~~~~~~~~~
 !!! error TS2322: Type '[number, string | number]' is not assignable to type '[number, string]'.

tests/baselines/reference/destructuringArrayBindingPatternAndAssignment2.errors.txt

@@ -4,8 +4,10 @@ tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAss
 tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAssignment2.ts(3,12): error TS2493: Tuple type '[]' of length '0' has no element at index '1'.
 tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAssignment2.ts(4,5): error TS2461: Type 'undefined' is not an array type.
 tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAssignment2.ts(9,51): error TS2322: Type 'number' is not assignable to type 'boolean'.
-tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAssignment2.ts(22,5): error TS2739: Type 'number[]' is missing the following properties from type '[number, number]': 0, 1
-tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAssignment2.ts(23,5): error TS2739: Type 'number[]' is missing the following properties from type '[string, string]': 0, 1
+tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAssignment2.ts(22,5): error TS2322: Type 'number[]' is not assignable to type '[number, number]'.
+  Target requires 2 element(s) but source may have fewer.
+tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAssignment2.ts(23,5): error TS2322: Type 'number[]' is not assignable to type '[string, string]'.
+  Target requires 2 element(s) but source may have fewer.
 tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAssignment2.ts(34,5): error TS2461: Type 'F' is not an array type.
 
 
@@ -45,10 +47,12 @@ tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAss
     var temp = [1, 2, 3]
     var [c0, c1]: [number, number] = [...temp];  // Error
         ~~~~~~~~
-!!! error TS2739: Type 'number[]' is missing the following properties from type '[number, number]': 0, 1
+!!! error TS2322: Type 'number[]' is not assignable to type '[number, number]'.
+!!! error TS2322:   Target requires 2 element(s) but source may have fewer.
     var [c2, c3]: [string, string] = [...temp];  // Error
         ~~~~~~~~
-!!! error TS2739: Type 'number[]' is missing the following properties from type '[string, string]': 0, 1
+!!! error TS2322: Type 'number[]' is not assignable to type '[string, string]'.
+!!! error TS2322:   Target requires 2 element(s) but source may have fewer.
     
     interface F {
         [idx: number]: boolean

tests/baselines/reference/destructuringParameterDeclaration1ES5.errors.txt

@@ -1,9 +1,7 @@
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5.ts(12,4): error TS2345: Argument of type '[number, number, string[][], number]' is not assignable to parameter of type '[number, number, string[][]]'.
-  Types of property 'length' are incompatible.
-    Type '4' is not assignable to type '3'.
+  Source has 4 element(s) but target allows only 3.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5.ts(57,4): error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-  Types of property 'length' are incompatible.
-    Type '5' is not assignable to type '3'.
+  Source has 5 element(s) but target allows only 3.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5.ts(62,10): error TS2393: Duplicate function implementation.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5.ts(63,10): error TS2393: Duplicate function implementation.
 
@@ -23,8 +21,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5.
     a1([1, 2, [["world"]], 3]);
        ~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, number, string[][], number]' is not assignable to parameter of type '[number, number, string[][]]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '4' is not assignable to type '3'.
+!!! error TS2345:   Source has 4 element(s) but target allows only 3.
     
     // If the declaration includes an initializer expression (which is permitted only
     // when the parameter list occurs in conjunction with a function body),
@@ -72,8 +69,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5.
     c5([1, 2, [["string"]], false, true]);  // Implied type is is [any, any, [[any]]]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '5' is not assignable to type '3'.
+!!! error TS2345:   Source has 5 element(s) but target allows only 3.
     
     // A parameter can be marked optional by following its name or binding pattern with a question mark (?)
     // or by including an initializer.

tests/baselines/reference/destructuringParameterDeclaration1ES5iterable.errors.txt

@@ -1,9 +1,7 @@
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5iterable.ts(12,4): error TS2345: Argument of type '[number, number, string[][], number]' is not assignable to parameter of type '[number, number, string[][]]'.
-  Types of property 'length' are incompatible.
-    Type '4' is not assignable to type '3'.
+  Source has 4 element(s) but target allows only 3.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5iterable.ts(57,4): error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-  Types of property 'length' are incompatible.
-    Type '5' is not assignable to type '3'.
+  Source has 5 element(s) but target allows only 3.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5iterable.ts(62,10): error TS2393: Duplicate function implementation.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5iterable.ts(63,10): error TS2393: Duplicate function implementation.
 
@@ -23,8 +21,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5i
     a1([1, 2, [["world"]], 3]);
        ~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, number, string[][], number]' is not assignable to parameter of type '[number, number, string[][]]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '4' is not assignable to type '3'.
+!!! error TS2345:   Source has 4 element(s) but target allows only 3.
     
     // If the declaration includes an initializer expression (which is permitted only
     // when the parameter list occurs in conjunction with a function body),
@@ -72,8 +69,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES5i
     c5([1, 2, [["string"]], false, true]);  // Implied type is is [any, any, [[any]]]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '5' is not assignable to type '3'.
+!!! error TS2345:   Source has 5 element(s) but target allows only 3.
     
     // A parameter can be marked optional by following its name or binding pattern with a question mark (?)
     // or by including an initializer.

tests/baselines/reference/destructuringParameterDeclaration1ES6.errors.txt

@@ -1,9 +1,7 @@
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES6.ts(14,4): error TS2345: Argument of type '[number, number, string[][], number]' is not assignable to parameter of type '[number, number, string[][]]'.
-  Types of property 'length' are incompatible.
-    Type '4' is not assignable to type '3'.
+  Source has 4 element(s) but target allows only 3.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES6.ts(58,4): error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-  Types of property 'length' are incompatible.
-    Type '5' is not assignable to type '3'.
+  Source has 5 element(s) but target allows only 3.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES6.ts(96,18): error TS2300: Duplicate identifier 'number'.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES6.ts(96,26): error TS2300: Duplicate identifier 'number'.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES6.ts(96,34): error TS2300: Duplicate identifier 'number'.
@@ -26,8 +24,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES6.
     a1([1, 2, [["world"]], 3]);
        ~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, number, string[][], number]' is not assignable to parameter of type '[number, number, string[][]]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '4' is not assignable to type '3'.
+!!! error TS2345:   Source has 4 element(s) but target allows only 3.
     
     
     // If the declaration includes an initializer expression (which is permitted only
@@ -74,8 +71,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration1ES6.
     c5([1, 2, [["string"]], false, true]);  // Implied type is is [any, any, [[any]]]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '5' is not assignable to type '3'.
+!!! error TS2345:   Source has 5 element(s) but target allows only 3.
     
     
     // A parameter can be marked optional by following its name or binding pattern with a question mark (?)

tests/baselines/reference/destructuringParameterDeclaration2.errors.txt

@@ -1,8 +1,7 @@
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration2.ts(7,8): error TS2322: Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration2.ts(7,29): error TS1005: ',' expected.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration2.ts(8,4): error TS2345: Argument of type '[number, number, string[][], string]' is not assignable to parameter of type '[number, number, string[][]]'.
-  Types of property 'length' are incompatible.
-    Type '4' is not assignable to type '3'.
+  Source has 4 element(s) but target allows only 3.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration2.ts(16,8): error TS2371: A parameter initializer is only allowed in a function or constructor implementation.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration2.ts(16,16): error TS2371: A parameter initializer is only allowed in a function or constructor implementation.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration2.ts(23,16): error TS2322: Type 'string' is not assignable to type 'number'.
@@ -43,8 +42,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration2.ts(
     a0([1, 2, [["world"]], "string"]);  // Error
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, number, string[][], string]' is not assignable to parameter of type '[number, number, string[][]]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '4' is not assignable to type '3'.
+!!! error TS2345:   Source has 4 element(s) but target allows only 3.
     
     
     // If the declaration includes an initializer expression (which is permitted only

tests/baselines/reference/destructuringParameterDeclaration3ES5.errors.txt

@@ -1,9 +1,8 @@
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5.ts(26,4): error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-  Types of property 'length' are incompatible.
-    Type '5' is not assignable to type '3'.
+  Source has 5 element(s) but target allows only 3.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5.ts(29,12): error TS2322: Type 'number' is not assignable to type '[[any]]'.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5.ts(30,5): error TS2345: Argument of type '[number, number]' is not assignable to parameter of type '[any, any, [[any]], ...any[]]'.
-  Property '2' is missing in type '[number, number]' but required in type '[any, any, [[any]], ...any[]]'.
+  Source has 2 element(s) but target requires 3.
 
 
 ==== tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5.ts (3 errors) ====
@@ -35,8 +34,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5.
     a9([1, 2, [["string"]], false, true]);   // Parameter type is [any, any, [[any]]]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '5' is not assignable to type '3'.
+!!! error TS2345:   Source has 5 element(s) but target allows only 3.
     
     a10([1, 2, [["string"]], false, true]);   // Parameter type is any[]
     a10([1, 2, 3, false, true]);              // Parameter type is any[]
@@ -45,7 +43,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5.
     a10([1, 2]);                              // Parameter type is any[]
         ~~~~~~
 !!! error TS2345: Argument of type '[number, number]' is not assignable to parameter of type '[any, any, [[any]], ...any[]]'.
-!!! error TS2345:   Property '2' is missing in type '[number, number]' but required in type '[any, any, [[any]], ...any[]]'.
+!!! error TS2345:   Source has 2 element(s) but target requires 3.
     a11([1, 2]);                              // Parameter type is number[]
     
     // Rest parameter with generic

tests/baselines/reference/destructuringParameterDeclaration3ES5iterable.errors.txt

@@ -1,9 +1,8 @@
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5iterable.ts(26,4): error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-  Types of property 'length' are incompatible.
-    Type '5' is not assignable to type '3'.
+  Source has 5 element(s) but target allows only 3.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5iterable.ts(29,12): error TS2322: Type 'number' is not assignable to type '[[any]]'.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5iterable.ts(30,5): error TS2345: Argument of type '[number, number]' is not assignable to parameter of type '[any, any, [[any]], ...any[]]'.
-  Property '2' is missing in type '[number, number]' but required in type '[any, any, [[any]], ...any[]]'.
+  Source has 2 element(s) but target requires 3.
 
 
 ==== tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5iterable.ts (3 errors) ====
@@ -35,8 +34,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5i
     a9([1, 2, [["string"]], false, true]);   // Parameter type is [any, any, [[any]]]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '5' is not assignable to type '3'.
+!!! error TS2345:   Source has 5 element(s) but target allows only 3.
     
     a10([1, 2, [["string"]], false, true]);   // Parameter type is any[]
     a10([1, 2, 3, false, true]);              // Parameter type is any[]
@@ -45,7 +43,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES5i
     a10([1, 2]);                              // Parameter type is any[]
         ~~~~~~
 !!! error TS2345: Argument of type '[number, number]' is not assignable to parameter of type '[any, any, [[any]], ...any[]]'.
-!!! error TS2345:   Property '2' is missing in type '[number, number]' but required in type '[any, any, [[any]], ...any[]]'.
+!!! error TS2345:   Source has 2 element(s) but target requires 3.
     a11([1, 2]);                              // Parameter type is number[]
     
     // Rest parameter with generic

tests/baselines/reference/destructuringParameterDeclaration3ES6.errors.txt

@@ -1,9 +1,8 @@
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES6.ts(26,4): error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-  Types of property 'length' are incompatible.
-    Type '5' is not assignable to type '3'.
+  Source has 5 element(s) but target allows only 3.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES6.ts(29,12): error TS2322: Type 'number' is not assignable to type '[[any]]'.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES6.ts(30,5): error TS2345: Argument of type '[number, number]' is not assignable to parameter of type '[any, any, [[any]], ...any[]]'.
-  Property '2' is missing in type '[number, number]' but required in type '[any, any, [[any]], ...any[]]'.
+  Source has 2 element(s) but target requires 3.
 
 
 ==== tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES6.ts (3 errors) ====
@@ -35,8 +34,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES6.
     a9([1, 2, [["string"]], false, true]);   // Parameter type is [any, any, [[any]]]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, number, [[string]], boolean, boolean]' is not assignable to parameter of type '[any, any, [[any]]]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '5' is not assignable to type '3'.
+!!! error TS2345:   Source has 5 element(s) but target allows only 3.
     
     a10([1, 2, [["string"]], false, true]);   // Parameter type is any[]
     a10([1, 2, 3, false, true]);              // Parameter type is any[]
@@ -45,7 +43,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration3ES6.
     a10([1, 2]);                              // Parameter type is any[]
         ~~~~~~
 !!! error TS2345: Argument of type '[number, number]' is not assignable to parameter of type '[any, any, [[any]], ...any[]]'.
-!!! error TS2345:   Property '2' is missing in type '[number, number]' but required in type '[any, any, [[any]], ...any[]]'.
+!!! error TS2345:   Source has 2 element(s) but target requires 3.
     a11([1, 2]);                              // Parameter type is number[]
     
     // Rest parameter with generic

tests/baselines/reference/destructuringParameterDeclaration4.errors.txt

@@ -4,7 +4,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration4.ts(
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration4.ts(21,7): error TS2552: Cannot find name 'array2'. Did you mean 'Array'?
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration4.ts(22,11): error TS2322: Type 'string' is not assignable to type '[[any]]'.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration4.ts(23,4): error TS2345: Argument of type '[number, number]' is not assignable to parameter of type '[any, any, [[any]]]'.
-  Property '2' is missing in type '[number, number]' but required in type '[any, any, [[any]]]'.
+  Source has 2 element(s) but target requires 3.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration4.ts(24,11): error TS2322: Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration4.ts(29,17): error TS1317: A parameter property cannot be declared using a rest parameter.
 tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration4.ts(34,22): error TS2304: Cannot find name 'E1'.
@@ -48,7 +48,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration4.ts(
     a5([1, 2]);                              // Error, parameter type is [any, any, [[any]]]
        ~~~~~~
 !!! error TS2345: Argument of type '[number, number]' is not assignable to parameter of type '[any, any, [[any]]]'.
-!!! error TS2345:   Property '2' is missing in type '[number, number]' but required in type '[any, any, [[any]]]'.
+!!! error TS2345:   Source has 2 element(s) but target requires 3.
     a6([1, 2, "string"]);                   // Error, parameter type is number[]
               ~~~~~~~~
 !!! error TS2322: Type 'string' is not assignable to type 'number'.

tests/baselines/reference/destructuringTuple.errors.txt

@@ -4,8 +4,7 @@ tests/cases/compiler/destructuringTuple.ts(11,48): error TS2769: No overload mat
     Type 'never[]' is not assignable to type 'number'.
   Overload 2 of 3, '(callbackfn: (previousValue: [], currentValue: number, currentIndex: number, array: number[]) => [], initialValue: []): []', gave the following error.
     Type 'never[]' is not assignable to type '[]'.
-      Types of property 'length' are incompatible.
-        Type 'number' is not assignable to type '0'.
+      Target allows only 0 element(s) but source may have more.
 tests/cases/compiler/destructuringTuple.ts(11,60): error TS2769: No overload matches this call.
   Overload 1 of 2, '(...items: ConcatArray<never>[]): never[]', gave the following error.
     Argument of type 'number' is not assignable to parameter of type 'ConcatArray<never>'.
@@ -33,8 +32,7 @@ tests/cases/compiler/destructuringTuple.ts(11,60): error TS2769: No overload mat
 !!! error TS2769:     Type 'never[]' is not assignable to type 'number'.
 !!! error TS2769:   Overload 2 of 3, '(callbackfn: (previousValue: [], currentValue: number, currentIndex: number, array: number[]) => [], initialValue: []): []', gave the following error.
 !!! error TS2769:     Type 'never[]' is not assignable to type '[]'.
-!!! error TS2769:       Types of property 'length' are incompatible.
-!!! error TS2769:         Type 'number' is not assignable to type '0'.
+!!! error TS2769:       Target allows only 0 element(s) but source may have more.
 !!! related TS6502 /.ts/lib.es5.d.ts:1368:24: The expected type comes from the return type of this signature.
 !!! related TS6502 /.ts/lib.es5.d.ts:1374:27: The expected type comes from the return type of this signature.
                                                                ~~

tests/baselines/reference/elementAccessChain.3.types

@@ -170,7 +170,7 @@ for (obj?.a["b"] of []);
 
 [...obj?.["a"]] = [];
 >[...obj?.["a"]] = [] : never[]
->[...obj?.["a"]] : never[]
+>[...obj?.["a"]] : any[]
 >...obj?.["a"] : any
 >obj?.["a"] : any
 >obj : any
@@ -179,7 +179,7 @@ for (obj?.a["b"] of []);
 
 [...obj?.a["b"]] = [];
 >[...obj?.a["b"]] = [] : never[]
->[...obj?.a["b"]] : never[]
+>[...obj?.a["b"]] : any[]
 >...obj?.a["b"] : any
 >obj?.a["b"] : any
 >obj?.a : any

tests/baselines/reference/emptyArrayDestructuringExpressionVisitedByTransformer.types

@@ -2,7 +2,7 @@
 var a = [] = [1].map(_ => _);
 >a : number[]
 >[] = [1].map(_ => _) : number[]
->[] : undefined[]
+>[] : []
 >[1].map(_ => _) : number[]
 >[1].map : <U>(callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]
 >[1] : number[]

tests/baselines/reference/emptyAssignmentPatterns01_ES5.types

@@ -11,7 +11,7 @@ var a: any;
 ([] = a);
 >([] = a) : any
 >[] = a : any
->[] : undefined[]
+>[] : []
 >a : any
 
 var [,] = [1,2];

tests/baselines/reference/emptyAssignmentPatterns01_ES5iterable.types

@@ -11,6 +11,6 @@ var a: any;
 ([] = a);
 >([] = a) : any
 >[] = a : any
->[] : undefined[]
+>[] : []
 >a : any
 

tests/baselines/reference/emptyAssignmentPatterns01_ES6.types

@@ -11,6 +11,6 @@ var a: any;
 ([] = a);
 >([] = a) : any
 >[] = a : any
->[] : undefined[]
+>[] : []
 >a : any
 

tests/baselines/reference/emptyAssignmentPatterns02_ES5.types

@@ -24,7 +24,7 @@ let x, y, z, a1, a2, a3;
 ([] = [ a1, a2, a3] = a);
 >([] = [ a1, a2, a3] = a) : any
 >[] = [ a1, a2, a3] = a : any
->[] : undefined[]
+>[] : []
 >[ a1, a2, a3] = a : any
 >[ a1, a2, a3] : [any, any, any]
 >a1 : any

tests/baselines/reference/emptyAssignmentPatterns02_ES5iterable.types

@@ -24,7 +24,7 @@ let x, y, z, a1, a2, a3;
 ([] = [ a1, a2, a3] = a);
 >([] = [ a1, a2, a3] = a) : any
 >[] = [ a1, a2, a3] = a : any
->[] : undefined[]
+>[] : []
 >[ a1, a2, a3] = a : any
 >[ a1, a2, a3] : [any, any, any]
 >a1 : any

tests/baselines/reference/emptyAssignmentPatterns02_ES6.types

@@ -24,7 +24,7 @@ let x, y, z, a1, a2, a3;
 ([] = [ a1, a2, a3] = a);
 >([] = [ a1, a2, a3] = a) : any
 >[] = [ a1, a2, a3] = a : any
->[] : undefined[]
+>[] : []
 >[ a1, a2, a3] = a : any
 >[ a1, a2, a3] : [any, any, any]
 >a1 : any

tests/baselines/reference/emptyAssignmentPatterns03_ES5.types

@@ -13,8 +13,8 @@ var a: any;
 ([] = [] = a);
 >([] = [] = a) : any
 >[] = [] = a : any
->[] : undefined[]
+>[] : []
 >[] = a : any
->[] : undefined[]
+>[] : []
 >a : any
 

tests/baselines/reference/emptyAssignmentPatterns03_ES5iterable.types

@@ -13,8 +13,8 @@ var a: any;
 ([] = [] = a);
 >([] = [] = a) : any
 >[] = [] = a : any
->[] : undefined[]
+>[] : []
 >[] = a : any
->[] : undefined[]
+>[] : []
 >a : any
 

tests/baselines/reference/emptyAssignmentPatterns03_ES6.types

@@ -13,8 +13,8 @@ var a: any;
 ([] = [] = a);
 >([] = [] = a) : any
 >[] = [] = a : any
->[] : undefined[]
+>[] : []
 >[] = a : any
->[] : undefined[]
+>[] : []
 >a : any
 

tests/baselines/reference/emptyAssignmentPatterns04_ES5.types

@@ -29,6 +29,6 @@ let x, y, z, a1, a2, a3;
 >a2 : any
 >a3 : any
 >[] = a : any
->[] : undefined[]
+>[] : []
 >a : any
 

tests/baselines/reference/emptyAssignmentPatterns04_ES5iterable.types

@@ -29,6 +29,6 @@ let x, y, z, a1, a2, a3;
 >a2 : any
 >a3 : any
 >[] = a : any
->[] : undefined[]
+>[] : []
 >a : any
 

tests/baselines/reference/emptyAssignmentPatterns04_ES6.types

@@ -29,6 +29,6 @@ let x, y, z, a1, a2, a3;
 >a2 : any
 >a3 : any
 >[] = a : any
->[] : undefined[]
+>[] : []
 >a : any
 

tests/baselines/reference/genericCallWithTupleType.errors.txt

@@ -1,6 +1,5 @@
 tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTupleType.ts(12,1): error TS2322: Type '[string, number, boolean, boolean]' is not assignable to type '[string, number]'.
-  Types of property 'length' are incompatible.
-    Type '4' is not assignable to type '2'.
+  Source has 4 element(s) but target allows only 2.
 tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTupleType.ts(13,20): error TS2493: Tuple type '[string, number]' of length '2' has no element at index '2'.
 tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTupleType.ts(14,1): error TS2322: Type '{ a: string; }' is not assignable to type 'undefined'.
 tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTupleType.ts(14,11): error TS2493: Tuple type '[string, number]' of length '2' has no element at index '3'.
@@ -9,7 +8,8 @@ tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTup
 tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTupleType.ts(22,17): error TS2322: Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTupleType.ts(23,14): error TS2322: Type '{}' is not assignable to type 'string'.
 tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTupleType.ts(23,18): error TS2322: Type '{}' is not assignable to type 'number'.
-tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTupleType.ts(24,1): error TS2741: Property '1' is missing in type '[{}]' but required in type '[{}, {}]'.
+tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTupleType.ts(24,1): error TS2322: Type '[{}]' is not assignable to type '[{}, {}]'.
+  Source has 1 element(s) but target requires 2.
 
 
 ==== tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTupleType.ts (10 errors) ====
@@ -27,8 +27,7 @@ tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTup
     i1.tuple1 = ["foo", 5, false, true];
     ~~~~~~~~~
 !!! error TS2322: Type '[string, number, boolean, boolean]' is not assignable to type '[string, number]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '4' is not assignable to type '2'.
+!!! error TS2322:   Source has 4 element(s) but target allows only 2.
     var e3 = i1.tuple1[2];  // {}
                        ~
 !!! error TS2493: Tuple type '[string, number]' of length '2' has no element at index '2'.
@@ -58,5 +57,6 @@ tests/cases/conformance/types/typeRelationships/typeInference/genericCallWithTup
 !!! error TS2322: Type '{}' is not assignable to type 'number'.
     i2.tuple1 = [{}];
     ~~~~~~~~~
-!!! error TS2741: Property '1' is missing in type '[{}]' but required in type '[{}, {}]'.
+!!! error TS2322: Type '[{}]' is not assignable to type '[{}, {}]'.
+!!! error TS2322:   Source has 1 element(s) but target requires 2.
     

tests/baselines/reference/genericRestParameters1.errors.txt

@@ -1,7 +1,3 @@
-tests/cases/conformance/types/rest/genericRestParameters1.ts(22,4): error TS2345: Argument of type 'string | number' is not assignable to parameter of type 'number'.
-  Type 'string' is not assignable to type 'number'.
-tests/cases/conformance/types/rest/genericRestParameters1.ts(31,4): error TS2345: Argument of type 'string | number' is not assignable to parameter of type 'number'.
-  Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/types/rest/genericRestParameters1.ts(135,23): error TS2344: Type 'Function' does not satisfy the constraint '(...args: any) => any'.
   Type 'Function' provides no match for the signature '(...args: any): any'.
 tests/cases/conformance/types/rest/genericRestParameters1.ts(164,1): error TS2322: Type '(a: never) => void' is not assignable to type '(...args: any[]) => void'.
@@ -9,7 +5,7 @@ tests/cases/conformance/types/rest/genericRestParameters1.ts(164,1): error TS232
     Type 'any' is not assignable to type 'never'.
 
 
-==== tests/cases/conformance/types/rest/genericRestParameters1.ts (4 errors) ====
+==== tests/cases/conformance/types/rest/genericRestParameters1.ts (2 errors) ====
     declare let f1: (...x: [number, string, boolean]) => void;
     declare let f2: (x0: number, x1: string, x2: boolean) => void;
     
@@ -32,9 +28,6 @@ tests/cases/conformance/types/rest/genericRestParameters1.ts(164,1): error TS232
     f1(42, "hello", true, ...t0);
     f1(ns[0], ns[1], true);
     f1(...ns, true);  // FIXME: Error, since ...ns is considered as string|number here
-       ~~~~~
-!!! error TS2345: Argument of type 'string | number' is not assignable to parameter of type 'number'.
-!!! error TS2345:   Type 'string' is not assignable to type 'number'.
     
     f2(42, "hello", true);
     f2(t3[0], t3[1], t3[2]);
@@ -44,9 +37,6 @@ tests/cases/conformance/types/rest/genericRestParameters1.ts(164,1): error TS232
     f2(42, "hello", true, ...t0);
     f2(ns[0], ns[1], true);
     f2(...ns, true);  // FIXME: Error, since ...ns is considered as string|number here
-       ~~~~~
-!!! error TS2345: Argument of type 'string | number' is not assignable to parameter of type 'number'.
-!!! error TS2345:   Type 'string' is not assignable to type 'number'.
     
     declare function f10<T extends unknown[]>(...args: T): T;
     

tests/baselines/reference/genericRestParameters1.js

@@ -296,7 +296,7 @@ declare const x14: [number, string, boolean];
 declare const x15: [number, string, boolean];
 declare const x16: [number, string, boolean];
 declare const x17: [number, string, boolean];
-declare const x18: (string | number | boolean)[];
+declare const x18: [number, string, boolean];
 declare function g10<U extends string[], V extends [number, number]>(u: U, v: V): void;
 declare function f11<T extends (string | number | boolean)[]>(...args: T): T;
 declare const z10: [42, "hello", true];
@@ -307,7 +307,7 @@ declare const z14: [number, string, boolean];
 declare const z15: [42, string, boolean];
 declare const z16: [42, "hello", boolean];
 declare const z17: [42, "hello", true];
-declare const z18: (string | number | true)[];
+declare const z18: [number, string, true];
 declare function g11<U extends string[], V extends [number, number]>(u: U, v: V): void;
 declare function call<T extends unknown[], U>(f: (...args: T) => U, ...args: T): U;
 declare function callr<T extends unknown[], U>(args: T, f: (...args: T) => U): U;

tests/baselines/reference/genericRestParameters1.types

@@ -238,8 +238,8 @@ const x17 = f10(42, "hello", true, ...t0);  // [number, string, boolean]
 >t0 : []
 
 const x18 = f10(...ns, true);  // (string | number | boolean)[]
->x18 : (string | number | boolean)[]
->f10(...ns, true) : (string | number | boolean)[]
+>x18 : [number, string, boolean]
+>f10(...ns, true) : [number, string, boolean]
 >f10 : <T extends unknown[]>(...args: T) => T
 >...ns : string | number
 >ns : [number, string]
@@ -265,16 +265,16 @@ function g10<U extends string[], V extends [number, number]>(u: U, v: V) {
 >v : V
 
     let x3 = f10(1, ...u);  // [number, ...string[]]
->x3 : [number, ...string[]]
->f10(1, ...u) : [number, ...string[]]
+>x3 : [number, ...U]
+>f10(1, ...u) : [number, ...U]
 >f10 : <T extends unknown[]>(...args: T) => T
 >1 : 1
 >...u : string
 >u : U
 
     let x4 = f10(...u, ...v);  // (string | number)[]
->x4 : (string | number)[]
->f10(...u, ...v) : (string | number)[]
+>x4 : [...U, ...V]
+>f10(...u, ...v) : [...U, ...V]
 >f10 : <T extends unknown[]>(...args: T) => T
 >...u : string
 >u : U
@@ -347,8 +347,8 @@ const z17 = f11(42, "hello", true, ...t0);  // [42, "hello", true]
 >t0 : []
 
 const z18 = f11(...ns, true);  // (string | number | true)[]
->z18 : (string | number | true)[]
->f11(...ns, true) : (string | number | true)[]
+>z18 : [number, string, true]
+>f11(...ns, true) : [number, string, true]
 >f11 : <T extends (string | number | boolean)[]>(...args: T) => T
 >...ns : string | number
 >ns : [number, string]
@@ -374,16 +374,16 @@ function g11<U extends string[], V extends [number, number]>(u: U, v: V) {
 >v : V
 
     let x3 = f11(1, ...u);  // [1, ...string[]]
->x3 : [1, ...string[]]
->f11(1, ...u) : [1, ...string[]]
+>x3 : [1, ...U]
+>f11(1, ...u) : [1, ...U]
 >f11 : <T extends (string | number | boolean)[]>(...args: T) => T
 >1 : 1
 >...u : string
 >u : U
 
     let x4 = f11(...u, ...v);  // (string | number)[]
->x4 : (string | number)[]
->f11(...u, ...v) : (string | number)[]
+>x4 : [...U, ...V]
+>f11(...u, ...v) : [...U, ...V]
 >f11 : <T extends (string | number | boolean)[]>(...args: T) => T
 >...u : string
 >u : U

tests/baselines/reference/genericRestParameters2.types

@@ -408,7 +408,7 @@ f20(42, "hello", ...t3);
 >t3 : boolean[]
 
 f20(42, "hello", ...t2, true);
->f20(42, "hello", ...t2, true) : [number, string, ...(string | boolean)[]]
+>f20(42, "hello", ...t2, true) : [number, string, string, ...boolean[]]
 >f20 : <T extends unknown[]>(...args: T) => T
 >42 : 42
 >"hello" : "hello"
@@ -437,7 +437,7 @@ type T04 = ConstructorParameters<new (...args: [number, string, ...boolean[]]) =
 >args : [number, string, ...boolean[]]
 
 type T05<T extends any[]> = Parameters<(x: string, ...args: T) => void>;
->T05 : Parameters<(x: string, ...args: T) => void>
+>T05 : [x: string, ...args: T]
 >x : string
 >args : T
 

tests/baselines/reference/genericRestParameters3.errors.txt

@@ -2,18 +2,19 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(17,11): error TS234
   Type '[10]' is not assignable to type '[string]'.
     Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(18,1): error TS2345: Argument of type '[]' is not assignable to parameter of type '[string] | [number, boolean]'.
-  Type '[]' is missing the following properties from type '[number, boolean]': 0, 1
+  Type '[]' is not assignable to type '[number, boolean]'.
+    Source has 0 element(s) but target requires 2.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(22,1): error TS2322: Type '(x: string, ...args: [string] | [number, boolean]) => void' is not assignable to type '(...args: [string, string] | [string, number, boolean]) => void'.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(23,1): error TS2322: Type '(x: string, y: string) => void' is not assignable to type '(x: string, ...args: [string] | [number, boolean]) => void'.
   Types of parameters 'y' and 'args' are incompatible.
     Type '[string] | [number, boolean]' is not assignable to type '[y: string]'.
       Type '[number, boolean]' is not assignable to type '[y: string]'.
-        Types of property '0' are incompatible.
-          Type 'number' is not assignable to type 'string'.
+        Source has 2 element(s) but target allows only 1.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(24,1): error TS2322: Type '(x: string, y: number, z: boolean) => void' is not assignable to type '(x: string, ...args: [string] | [number, boolean]) => void'.
   Types of parameters 'y' and 'args' are incompatible.
     Type '[string] | [number, boolean]' is not assignable to type '[y: number, z: boolean]'.
-      Property '1' is missing in type '[string]' but required in type '[y: number, z: boolean]'.
+      Type '[string]' is not assignable to type '[y: number, z: boolean]'.
+        Source has 1 element(s) but target requires 2.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(25,1): error TS2322: Type '(...args: [string, string] | [string, number, boolean]) => void' is not assignable to type '(x: string, ...args: [string] | [number, boolean]) => void'.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(35,1): error TS2554: Expected 1 arguments, but got 0.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(36,21): error TS2345: Argument of type 'number' is not assignable to parameter of type '(...args: CoolArray<any>) => void'.
@@ -31,7 +32,8 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(51,5): error TS2345
 tests/cases/conformance/types/rest/genericRestParameters3.ts(52,5): error TS2345: Argument of type 'number[]' is not assignable to parameter of type 'CoolArray<number>'.
   Property 'hello' is missing in type 'number[]' but required in type 'CoolArray<number>'.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(59,5): error TS2345: Argument of type '["what"]' is not assignable to parameter of type '[] | [number, string]'.
-  Property '1' is missing in type '["what"]' but required in type '[number, string]'.
+  Type '["what"]' is not assignable to type '[number, string]'.
+    Source has 1 element(s) but target requires 2.
 
 
 ==== tests/cases/conformance/types/rest/genericRestParameters3.ts (15 errors) ====
@@ -59,7 +61,8 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(59,5): error TS2345
     f1("foo");  // Error
     ~~~~~~~~~
 !!! error TS2345: Argument of type '[]' is not assignable to parameter of type '[string] | [number, boolean]'.
-!!! error TS2345:   Type '[]' is missing the following properties from type '[number, boolean]': 0, 1
+!!! error TS2345:   Type '[]' is not assignable to type '[number, boolean]'.
+!!! error TS2345:     Source has 0 element(s) but target requires 2.
     
     f2 = f1;
     f3 = f1;
@@ -72,14 +75,14 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(59,5): error TS2345
 !!! error TS2322:   Types of parameters 'y' and 'args' are incompatible.
 !!! error TS2322:     Type '[string] | [number, boolean]' is not assignable to type '[y: string]'.
 !!! error TS2322:       Type '[number, boolean]' is not assignable to type '[y: string]'.
-!!! error TS2322:         Types of property '0' are incompatible.
-!!! error TS2322:           Type 'number' is not assignable to type 'string'.
+!!! error TS2322:         Source has 2 element(s) but target allows only 1.
     f1 = f3;  // Error
     ~~
 !!! error TS2322: Type '(x: string, y: number, z: boolean) => void' is not assignable to type '(x: string, ...args: [string] | [number, boolean]) => void'.
 !!! error TS2322:   Types of parameters 'y' and 'args' are incompatible.
 !!! error TS2322:     Type '[string] | [number, boolean]' is not assignable to type '[y: number, z: boolean]'.
-!!! error TS2322:       Property '1' is missing in type '[string]' but required in type '[y: number, z: boolean]'.
+!!! error TS2322:       Type '[string]' is not assignable to type '[y: number, z: boolean]'.
+!!! error TS2322:         Source has 1 element(s) but target requires 2.
     f1 = f4;  // Error, misaligned complex rest types
     ~~
 !!! error TS2322: Type '(...args: [string, string] | [string, number, boolean]) => void' is not assignable to type '(x: string, ...args: [string] | [number, boolean]) => void'.
@@ -148,7 +151,8 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(59,5): error TS2345
     hmm("what"); // no error?  A = [] | [number, string] ?
         ~~~~~~
 !!! error TS2345: Argument of type '["what"]' is not assignable to parameter of type '[] | [number, string]'.
-!!! error TS2345:   Property '1' is missing in type '["what"]' but required in type '[number, string]'.
+!!! error TS2345:   Type '["what"]' is not assignable to type '[number, string]'.
+!!! error TS2345:     Source has 1 element(s) but target requires 2.
     
     // Repro from #35066
     

tests/baselines/reference/genericRestTypes.errors.txt

@@ -1,7 +1,7 @@
 tests/cases/compiler/genericRestTypes.ts(21,11): error TS2322: Type '(cb: (x: string, ...rest: T) => void) => void' is not assignable to type '(cb: (...args: never) => void) => void'.
   Types of parameters 'cb' and 'cb' are incompatible.
     Types of parameters 'args' and 'x' are incompatible.
-      Type '[x: string, ...rest: T[number][]]' is not assignable to type 'never'.
+      Type '[x: string, ...rest: T]' is not assignable to type 'never'.
 
 
 ==== tests/cases/compiler/genericRestTypes.ts (1 errors) ====
@@ -30,7 +30,7 @@ tests/cases/compiler/genericRestTypes.ts(21,11): error TS2322: Type '(cb: (x: st
 !!! error TS2322: Type '(cb: (x: string, ...rest: T) => void) => void' is not assignable to type '(cb: (...args: never) => void) => void'.
 !!! error TS2322:   Types of parameters 'cb' and 'cb' are incompatible.
 !!! error TS2322:     Types of parameters 'args' and 'x' are incompatible.
-!!! error TS2322:       Type '[x: string, ...rest: T[number][]]' is not assignable to type 'never'.
+!!! error TS2322:       Type '[x: string, ...rest: T]' is not assignable to type 'never'.
     }
     
     function assignmentWithComplexRest3<T extends any[]>() {

tests/baselines/reference/namedTupleMembersErrors.errors.txt

@@ -7,8 +7,8 @@ tests/cases/conformance/types/tuple/named/namedTupleMembersErrors.ts(11,49): err
 tests/cases/conformance/types/tuple/named/namedTupleMembersErrors.ts(11,52): error TS8020: JSDoc types can only be used inside documentation comments.
 tests/cases/conformance/types/tuple/named/namedTupleMembersErrors.ts(13,39): error TS5085: A tuple member cannot be both optional and rest.
 tests/cases/conformance/types/tuple/named/namedTupleMembersErrors.ts(15,44): error TS2574: A rest element type must be an array type.
-tests/cases/conformance/types/tuple/named/namedTupleMembersErrors.ts(17,46): error TS2574: A rest element type must be an array type.
-tests/cases/conformance/types/tuple/named/namedTupleMembersErrors.ts(18,44): error TS2574: A rest element type must be an array type.
+tests/cases/conformance/types/tuple/named/namedTupleMembersErrors.ts(17,13): error TS2456: Type alias 'RecusiveRestUnlabeled' circularly references itself.
+tests/cases/conformance/types/tuple/named/namedTupleMembersErrors.ts(18,13): error TS2456: Type alias 'RecusiveRest' circularly references itself.
 
 
 ==== tests/cases/conformance/types/tuple/named/namedTupleMembersErrors.ts (11 errors) ====
@@ -47,9 +47,9 @@ tests/cases/conformance/types/tuple/named/namedTupleMembersErrors.ts(18,44): err
 !!! error TS2574: A rest element type must be an array type.
     
     export type RecusiveRestUnlabeled = [string, ...RecusiveRestUnlabeled];
-                                                 ~~~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS2574: A rest element type must be an array type.
+                ~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2456: Type alias 'RecusiveRestUnlabeled' circularly references itself.
     export type RecusiveRest = [first: string, ...rest: RecusiveRest]; // marked as incorrect, same as above
-                                               ~~~~~~~~~~~~~~~~~~~~~
-!!! error TS2574: A rest element type must be an array type.
+                ~~~~~~~~~~~~
+!!! error TS2456: Type alias 'RecusiveRest' circularly references itself.
     

tests/baselines/reference/namedTupleMembersErrors.types

@@ -3,7 +3,7 @@ export type Segment1 = [length: number, number]; // partially named, disallowed
 >Segment1 : Segment1
 
 export type List = [item: any, ...any];  // partially named, disallowed
->List : List
+>List : [any, ...any[]]
 
 export type Pair = [item: any, any?];  // partially named, disallowed
 >Pair : Pair
@@ -21,11 +21,11 @@ export type OptRest = [first: string, ...rest?: string[]]; // rest+optional disa
 >OptRest : OptRest
 
 export type NonArrayRest = [first: string, ...rest: number]; // non-arraylike rest, disallowed
->NonArrayRest : NonArrayRest
+>NonArrayRest : [first: string, ...rest: any[]]
 
 export type RecusiveRestUnlabeled = [string, ...RecusiveRestUnlabeled];
->RecusiveRestUnlabeled : RecusiveRestUnlabeled
+>RecusiveRestUnlabeled : any
 
 export type RecusiveRest = [first: string, ...rest: RecusiveRest]; // marked as incorrect, same as above
->RecusiveRest : RecusiveRest
+>RecusiveRest : any
 

tests/baselines/reference/namespaceDisambiguationInUnion.errors.txt

@@ -2,7 +2,8 @@ tests/cases/compiler/namespaceDisambiguationInUnion.ts(10,7): error TS2322: Type
   Type '{ type: string; }' is not assignable to type 'Yep'.
     Types of property 'type' are incompatible.
       Type 'string' is not assignable to type '"bar.yep"'.
-tests/cases/compiler/namespaceDisambiguationInUnion.ts(13,7): error TS2739: Type '{ type: string; }[]' is missing the following properties from type '[Foo.Yep, Bar.Yep]': 0, 1
+tests/cases/compiler/namespaceDisambiguationInUnion.ts(13,7): error TS2322: Type '{ type: string; }[]' is not assignable to type '[Foo.Yep, Bar.Yep]'.
+  Target requires 2 element(s) but source may have fewer.
 
 
 ==== tests/cases/compiler/namespaceDisambiguationInUnion.ts (2 errors) ====
@@ -25,5 +26,6 @@ tests/cases/compiler/namespaceDisambiguationInUnion.ts(13,7): error TS2739: Type
     const y = [{ type: "a" }, { type: "b" }];
     const val2: [Foo.Yep, Bar.Yep] = y;
           ~~~~
-!!! error TS2739: Type '{ type: string; }[]' is missing the following properties from type '[Foo.Yep, Bar.Yep]': 0, 1
+!!! error TS2322: Type '{ type: string; }[]' is not assignable to type '[Foo.Yep, Bar.Yep]'.
+!!! error TS2322:   Target requires 2 element(s) but source may have fewer.
     

tests/baselines/reference/nonIterableRestElement1.types

@@ -5,7 +5,7 @@ var c = {};
 
 [...c] = ["", 0];
 >[...c] = ["", 0] : (string | number)[]
->[...c] : undefined[]
+>[...c] : unknown[]
 >...c : any
 >c : {}
 >["", 0] : (string | number)[]

tests/baselines/reference/nonIterableRestElement2.types

@@ -5,7 +5,7 @@ var c = {};
 
 [...c] = ["", 0];
 >[...c] = ["", 0] : (string | number)[]
->[...c] : undefined[]
+>[...c] : unknown[]
 >...c : any
 >c : {}
 >["", 0] : (string | number)[]

tests/baselines/reference/nonIterableRestElement3.types

@@ -7,7 +7,7 @@ var c = { bogus: 0 };
 
 [...c] = ["", 0];
 >[...c] = ["", 0] : (string | number)[]
->[...c] : undefined[]
+>[...c] : unknown[]
 >...c : any
 >c : { bogus: number; }
 >["", 0] : (string | number)[]

tests/baselines/reference/optionalTupleElements1.errors.txt

@@ -1,28 +1,16 @@
 tests/cases/conformance/types/tuple/optionalTupleElements1.ts(11,29): error TS1257: A required element cannot follow an optional element.
 tests/cases/conformance/types/tuple/optionalTupleElements1.ts(15,5): error TS2322: Type 'T2' is not assignable to type 'T1'.
-  Types of property '2' are incompatible.
-    Type 'boolean | undefined' is not assignable to type 'boolean'.
-      Type 'undefined' is not assignable to type 'boolean'.
+  Property '2' is optional in type '[number, string, (boolean | undefined)?]' but required in type '[number, string, boolean]'.
 tests/cases/conformance/types/tuple/optionalTupleElements1.ts(16,5): error TS2322: Type 'T3' is not assignable to type 'T1'.
-  Types of property '1' are incompatible.
-    Type 'string | undefined' is not assignable to type 'string'.
-      Type 'undefined' is not assignable to type 'string'.
+  Property '1' is optional in type '[number, (string | undefined)?, (boolean | undefined)?]' but required in type '[number, string, boolean]'.
 tests/cases/conformance/types/tuple/optionalTupleElements1.ts(17,5): error TS2322: Type 'T4' is not assignable to type 'T1'.
-  Types of property '0' are incompatible.
-    Type 'number | undefined' is not assignable to type 'number'.
-      Type 'undefined' is not assignable to type 'number'.
+  Property '0' is optional in type '[(number | undefined)?, (string | undefined)?, (boolean | undefined)?]' but required in type '[number, string, boolean]'.
 tests/cases/conformance/types/tuple/optionalTupleElements1.ts(20,5): error TS2322: Type 'T3' is not assignable to type 'T2'.
-  Types of property '1' are incompatible.
-    Type 'string | undefined' is not assignable to type 'string'.
-      Type 'undefined' is not assignable to type 'string'.
+  Property '1' is optional in type '[number, (string | undefined)?, (boolean | undefined)?]' but required in type '[number, string, (boolean | undefined)?]'.
 tests/cases/conformance/types/tuple/optionalTupleElements1.ts(21,5): error TS2322: Type 'T4' is not assignable to type 'T2'.
-  Types of property '0' are incompatible.
-    Type 'number | undefined' is not assignable to type 'number'.
-      Type 'undefined' is not assignable to type 'number'.
+  Property '0' is optional in type '[(number | undefined)?, (string | undefined)?, (boolean | undefined)?]' but required in type '[number, string, (boolean | undefined)?]'.
 tests/cases/conformance/types/tuple/optionalTupleElements1.ts(25,5): error TS2322: Type 'T4' is not assignable to type 'T3'.
-  Types of property '0' are incompatible.
-    Type 'number | undefined' is not assignable to type 'number'.
-      Type 'undefined' is not assignable to type 'number'.
+  Property '0' is optional in type '[(number | undefined)?, (string | undefined)?, (boolean | undefined)?]' but required in type '[number, (string | undefined)?, (boolean | undefined)?]'.
 
 
 ==== tests/cases/conformance/types/tuple/optionalTupleElements1.ts (7 errors) ====
@@ -45,44 +33,32 @@ tests/cases/conformance/types/tuple/optionalTupleElements1.ts(25,5): error TS232
         t1 = t2;  // Error
         ~~
 !!! error TS2322: Type 'T2' is not assignable to type 'T1'.
-!!! error TS2322:   Types of property '2' are incompatible.
-!!! error TS2322:     Type 'boolean | undefined' is not assignable to type 'boolean'.
-!!! error TS2322:       Type 'undefined' is not assignable to type 'boolean'.
+!!! error TS2322:   Property '2' is optional in type '[number, string, (boolean | undefined)?]' but required in type '[number, string, boolean]'.
         t1 = t3;  // Error
         ~~
 !!! error TS2322: Type 'T3' is not assignable to type 'T1'.
-!!! error TS2322:   Types of property '1' are incompatible.
-!!! error TS2322:     Type 'string | undefined' is not assignable to type 'string'.
-!!! error TS2322:       Type 'undefined' is not assignable to type 'string'.
+!!! error TS2322:   Property '1' is optional in type '[number, (string | undefined)?, (boolean | undefined)?]' but required in type '[number, string, boolean]'.
         t1 = t4;  // Error
         ~~
 !!! error TS2322: Type 'T4' is not assignable to type 'T1'.
-!!! error TS2322:   Types of property '0' are incompatible.
-!!! error TS2322:     Type 'number | undefined' is not assignable to type 'number'.
-!!! error TS2322:       Type 'undefined' is not assignable to type 'number'.
+!!! error TS2322:   Property '0' is optional in type '[(number | undefined)?, (string | undefined)?, (boolean | undefined)?]' but required in type '[number, string, boolean]'.
         t2 = t1;
         t2 = t2;
         t2 = t3;  // Error
         ~~
 !!! error TS2322: Type 'T3' is not assignable to type 'T2'.
-!!! error TS2322:   Types of property '1' are incompatible.
-!!! error TS2322:     Type 'string | undefined' is not assignable to type 'string'.
-!!! error TS2322:       Type 'undefined' is not assignable to type 'string'.
+!!! error TS2322:   Property '1' is optional in type '[number, (string | undefined)?, (boolean | undefined)?]' but required in type '[number, string, (boolean | undefined)?]'.
         t2 = t4;  // Error
         ~~
 !!! error TS2322: Type 'T4' is not assignable to type 'T2'.
-!!! error TS2322:   Types of property '0' are incompatible.
-!!! error TS2322:     Type 'number | undefined' is not assignable to type 'number'.
-!!! error TS2322:       Type 'undefined' is not assignable to type 'number'.
+!!! error TS2322:   Property '0' is optional in type '[(number | undefined)?, (string | undefined)?, (boolean | undefined)?]' but required in type '[number, string, (boolean | undefined)?]'.
         t3 = t1;
         t3 = t2;
         t3 = t3;
         t3 = t4;  // Error
         ~~
 !!! error TS2322: Type 'T4' is not assignable to type 'T3'.
-!!! error TS2322:   Types of property '0' are incompatible.
-!!! error TS2322:     Type 'number | undefined' is not assignable to type 'number'.
-!!! error TS2322:       Type 'undefined' is not assignable to type 'number'.
+!!! error TS2322:   Property '0' is optional in type '[(number | undefined)?, (string | undefined)?, (boolean | undefined)?]' but required in type '[number, (string | undefined)?, (boolean | undefined)?]'.
         t4 = t1;
         t4 = t2;
         t4 = t3;

tests/baselines/reference/promiseEmptyTupleNoException.errors.txt

@@ -1,6 +1,5 @@
 tests/cases/compiler/promiseEmptyTupleNoException.ts(3,3): error TS2322: Type 'any[]' is not assignable to type '[]'.
-  Types of property 'length' are incompatible.
-    Type 'number' is not assignable to type '0'.
+  Target allows only 0 element(s) but source may have more.
 
 
 ==== tests/cases/compiler/promiseEmptyTupleNoException.ts (1 errors) ====
@@ -9,7 +8,6 @@ tests/cases/compiler/promiseEmptyTupleNoException.ts(3,3): error TS2322: Type 'a
       return emails;
       ~~~~~~~~~~~~~~
 !!! error TS2322: Type 'any[]' is not assignable to type '[]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type 'number' is not assignable to type '0'.
+!!! error TS2322:   Target allows only 0 element(s) but source may have more.
     }
     

tests/baselines/reference/propertyAccessChain.3.types

@@ -170,7 +170,7 @@ for (obj?.a.b of []);
 
 [...obj?.a] = [];
 >[...obj?.a] = [] : never[]
->[...obj?.a] : never[]
+>[...obj?.a] : any[]
 >...obj?.a : any
 >obj?.a : any
 >obj : any
@@ -179,7 +179,7 @@ for (obj?.a.b of []);
 
 [...obj?.a.b] = [];
 >[...obj?.a.b] = [] : never[]
->[...obj?.a.b] : never[]
+>[...obj?.a.b] : any[]
 >...obj?.a.b : any
 >obj?.a.b : any
 >obj?.a : any

tests/baselines/reference/ramdaToolsNoInfinite.types

@@ -54,7 +54,7 @@ declare namespace Tools {
         T['length'];
 
     type Prepend<E, T extends any[]> =
->Prepend : Prepend<E, T>
+>Prepend : [head: E, ...args: T]
 
         ((head: E, ...args: T) => any) extends ((...args: infer U) => any)
 >head : E
@@ -68,7 +68,7 @@ declare namespace Tools {
 >Drop : Drop<N, T, I>
 
         0: Drop<N, Tail<T>, Prepend<any, I>>;
->0 : Drop<N, Tail<T>, Prepend<any, I>>
+>0 : Drop<N, Tail<T>, [head: any, ...args: I]>
 
         1: T;
 >1 : T
@@ -88,7 +88,7 @@ declare namespace Tools {
         Length<I>;
 
     type Next<I extends any[]> =
->Next : Prepend<any, I>
+>Next : [head: any, ...args: I]
 
         Prepend<any, I>;
 
@@ -101,7 +101,7 @@ declare namespace Tools {
 >Iterator : Iterator<Index, From, I>
 
         0: Iterator<Index, Next<From>, Next<I>>;
->0 : Iterator<Index, Prepend<any, From>, Prepend<any, I>>
+>0 : Iterator<Index, [head: any, ...args: From], [head: any, ...args: I]>
 
         1: From;
 >1 : From
@@ -116,7 +116,7 @@ declare namespace Tools {
 >Reverse : Reverse<T, R, I>
 
         0: Reverse<T, Prepend<T[Pos<I>], R>, Next<I>>;
->0 : Reverse<T, Prepend<T[Length<I>], R>, Prepend<any, I>>
+>0 : Reverse<T, [head: T[Length<I>], ...args: R], [head: any, ...args: I]>
 
         1: R;
 >1 : R
@@ -163,7 +163,7 @@ declare namespace Curry {
 
     interface GapsOfWorker<T1 extends any[], T2 extends any[], TN extends any[] = [], I extends any[] = []> {
         0: GapsOf<T1, T2, GapOf<T1, T2, TN, I> extends infer G ? Tools.Cast<G, any[]> : never, Tools.Next<I>>;
->0 : GapsOf<T1, T2, GapOf<T1, T2, TN, I> extends infer G ? Tools.Cast<G, any[]> : never, Tools.Prepend<any, I>>
+>0 : GapsOf<T1, T2, GapOf<T1, T2, TN, I> extends infer G ? Tools.Cast<G, any[]> : never, [head: any, ...args: I]>
 >Tools : any
 >Tools : any
 

tests/baselines/reference/readonlyArraysAndTuples.errors.txt

@@ -4,11 +4,14 @@ tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(11,12): error TS1
 tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(12,12): error TS1354: 'readonly' type modifier is only permitted on array and tuple literal types.
 tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(15,5): error TS4104: The type 'readonly string[]' is 'readonly' and cannot be assigned to the mutable type 'string[]'.
 tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(17,5): error TS4104: The type 'readonly [string, string]' is 'readonly' and cannot be assigned to the mutable type 'string[]'.
-tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(21,5): error TS2739: Type 'string[]' is missing the following properties from type '[string, string]': 0, 1
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(21,5): error TS2322: Type 'string[]' is not assignable to type '[string, string]'.
+  Target requires 2 element(s) but source may have fewer.
 tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(22,5): error TS4104: The type 'readonly string[]' is 'readonly' and cannot be assigned to the mutable type '[string, string]'.
 tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(23,5): error TS4104: The type 'readonly [string, string]' is 'readonly' and cannot be assigned to the mutable type '[string, string]'.
-tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(24,5): error TS2739: Type 'string[]' is missing the following properties from type 'readonly [string, string]': 0, 1
-tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(25,5): error TS2739: Type 'readonly string[]' is missing the following properties from type 'readonly [string, string]': 0, 1
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(24,5): error TS2322: Type 'string[]' is not assignable to type 'readonly [string, string]'.
+  Target requires 2 element(s) but source may have fewer.
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(25,5): error TS2322: Type 'readonly string[]' is not assignable to type 'readonly [string, string]'.
+  Target requires 2 element(s) but source may have fewer.
 tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(30,3): error TS2540: Cannot assign to '0' because it is a read-only property.
 tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(31,3): error TS2540: Cannot assign to '1' because it is a read-only property.
 tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(32,1): error TS2542: Index signature in type 'readonly [number, number, ...number[]]' only permits reading.
@@ -53,7 +56,8 @@ tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(36,8): error TS25
         ra = rt;
         mt = ma;  // Error
         ~~
-!!! error TS2739: Type 'string[]' is missing the following properties from type '[string, string]': 0, 1
+!!! error TS2322: Type 'string[]' is not assignable to type '[string, string]'.
+!!! error TS2322:   Target requires 2 element(s) but source may have fewer.
         mt = ra;  // Error
         ~~
 !!! error TS4104: The type 'readonly string[]' is 'readonly' and cannot be assigned to the mutable type '[string, string]'.
@@ -62,10 +66,12 @@ tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(36,8): error TS25
 !!! error TS4104: The type 'readonly [string, string]' is 'readonly' and cannot be assigned to the mutable type '[string, string]'.
         rt = ma;  // Error
         ~~
-!!! error TS2739: Type 'string[]' is missing the following properties from type 'readonly [string, string]': 0, 1
+!!! error TS2322: Type 'string[]' is not assignable to type 'readonly [string, string]'.
+!!! error TS2322:   Target requires 2 element(s) but source may have fewer.
         rt = ra;  // Error
         ~~
-!!! error TS2739: Type 'readonly string[]' is missing the following properties from type 'readonly [string, string]': 0, 1
+!!! error TS2322: Type 'readonly string[]' is not assignable to type 'readonly [string, string]'.
+!!! error TS2322:   Target requires 2 element(s) but source may have fewer.
         rt = mt;
     }
     

tests/baselines/reference/readonlyTupleAndArrayElaboration.errors.txt

@@ -11,15 +11,12 @@ tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(23,9): error TS2345: Ar
 tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(24,9): error TS2345: Argument of type 'readonly number[]' is not assignable to parameter of type 'number[]'.
   The type 'readonly number[]' is 'readonly' and cannot be assigned to the mutable type 'number[]'.
 tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(27,7): error TS2322: Type 'readonly [1]' is not assignable to type 'readonly []'.
-  Types of property 'length' are incompatible.
-    Type '1' is not assignable to type '0'.
+  Source has 1 element(s) but target allows only 0.
 tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(30,7): error TS4104: The type 'readonly [1]' is 'readonly' and cannot be assigned to the mutable type '[]'.
 tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(33,7): error TS2322: Type '[1]' is not assignable to type 'readonly []'.
-  Types of property 'length' are incompatible.
-    Type '1' is not assignable to type '0'.
+  Source has 1 element(s) but target allows only 0.
 tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(36,7): error TS2322: Type '[1]' is not assignable to type '[]'.
-  Types of property 'length' are incompatible.
-    Type '1' is not assignable to type '0'.
+  Source has 1 element(s) but target allows only 0.
 tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(39,7): error TS2322: Type 'readonly number[]' is not assignable to type 'readonly boolean[]'.
   Type 'number' is not assignable to type 'boolean'.
 tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(42,7): error TS4104: The type 'readonly number[]' is 'readonly' and cannot be assigned to the mutable type 'boolean[]'.
@@ -34,10 +31,13 @@ tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(57,7): error TS2322: Ty
   Type '1' is not assignable to type 'boolean'.
 tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(60,7): error TS2322: Type '[1]' is not assignable to type 'boolean[]'.
   Type '1' is not assignable to type 'boolean'.
-tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(63,7): error TS2741: Property '0' is missing in type 'readonly number[]' but required in type 'readonly [1]'.
+tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(63,7): error TS2322: Type 'readonly number[]' is not assignable to type 'readonly [1]'.
+  Target requires 1 element(s) but source may have fewer.
 tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(66,7): error TS4104: The type 'readonly number[]' is 'readonly' and cannot be assigned to the mutable type '[1]'.
-tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(69,7): error TS2741: Property '0' is missing in type 'number[]' but required in type 'readonly [1]'.
-tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(72,7): error TS2741: Property '0' is missing in type 'number[]' but required in type '[1]'.
+tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(69,7): error TS2322: Type 'number[]' is not assignable to type 'readonly [1]'.
+  Target requires 1 element(s) but source may have fewer.
+tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(72,7): error TS2322: Type 'number[]' is not assignable to type '[1]'.
+  Target requires 1 element(s) but source may have fewer.
 
 
 ==== tests/cases/compiler/readonlyTupleAndArrayElaboration.ts (22 errors) ====
@@ -88,8 +88,7 @@ tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(72,7): error TS2741: Pr
     const t2: readonly [] = t1;
           ~~
 !!! error TS2322: Type 'readonly [1]' is not assignable to type 'readonly []'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '1' is not assignable to type '0'.
+!!! error TS2322:   Source has 1 element(s) but target allows only 0.
     
     const t3: readonly [1] = [1];
     const t4: [] = t3;
@@ -100,15 +99,13 @@ tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(72,7): error TS2741: Pr
     const t6: readonly [] = t5;
           ~~
 !!! error TS2322: Type '[1]' is not assignable to type 'readonly []'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '1' is not assignable to type '0'.
+!!! error TS2322:   Source has 1 element(s) but target allows only 0.
     
     const t7: [1] = [1];
     const t8: [] = t7;
           ~~
 !!! error TS2322: Type '[1]' is not assignable to type '[]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '1' is not assignable to type '0'.
+!!! error TS2322:   Source has 1 element(s) but target allows only 0.
     
     const a1: readonly number[] = [1];
     const a2: readonly boolean[] = a1;
@@ -159,7 +156,8 @@ tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(72,7): error TS2741: Pr
     const at1: readonly number[] = [1];
     const at2: readonly [1] = at1;
           ~~~
-!!! error TS2741: Property '0' is missing in type 'readonly number[]' but required in type 'readonly [1]'.
+!!! error TS2322: Type 'readonly number[]' is not assignable to type 'readonly [1]'.
+!!! error TS2322:   Target requires 1 element(s) but source may have fewer.
     
     const at3: readonly number[] = [1];
     const at4: [1] = at3;
@@ -169,10 +167,12 @@ tests/cases/compiler/readonlyTupleAndArrayElaboration.ts(72,7): error TS2741: Pr
     const at5: number[] = [1];
     const at6: readonly [1] = at5;
           ~~~
-!!! error TS2741: Property '0' is missing in type 'number[]' but required in type 'readonly [1]'.
+!!! error TS2322: Type 'number[]' is not assignable to type 'readonly [1]'.
+!!! error TS2322:   Target requires 1 element(s) but source may have fewer.
     
     const at7: number[] = [1];
     const at8: [1] = at7;
           ~~~
-!!! error TS2741: Property '0' is missing in type 'number[]' but required in type '[1]'.
+!!! error TS2322: Type 'number[]' is not assignable to type '[1]'.
+!!! error TS2322:   Target requires 1 element(s) but source may have fewer.
     

tests/baselines/reference/recursiveResolveTypeMembers.errors.txt

@@ -1,10 +1,9 @@
 tests/cases/compiler/recursiveResolveTypeMembers.ts(4,49): error TS2577: Return type annotation circularly references itself.
 tests/cases/compiler/recursiveResolveTypeMembers.ts(4,58): error TS2304: Cannot find name 'H'.
-tests/cases/compiler/recursiveResolveTypeMembers.ts(4,62): error TS2574: A rest element type must be an array type.
 tests/cases/compiler/recursiveResolveTypeMembers.ts(4,79): error TS2304: Cannot find name 'R'.
 
 
-==== tests/cases/compiler/recursiveResolveTypeMembers.ts (4 errors) ====
+==== tests/cases/compiler/recursiveResolveTypeMembers.ts (3 errors) ====
     // Repro from #25291
     
     type PromisedTuple<L extends any[], U = (...args: L) => void> =
@@ -13,8 +12,6 @@ tests/cases/compiler/recursiveResolveTypeMembers.ts(4,79): error TS2304: Cannot
 !!! error TS2577: Return type annotation circularly references itself.
                                                              ~
 !!! error TS2304: Cannot find name 'H'.
-                                                                 ~~~~~~~~~~~~~~~~~~~
-!!! error TS2574: A rest element type must be an array type.
                                                                                   ~
 !!! error TS2304: Cannot find name 'R'.
     

tests/baselines/reference/restElementWithAssignmentPattern2.types

@@ -5,7 +5,7 @@ var a: string, b: number;
 
 [...{ 0: a = "", b }] = ["", 1];
 >[...{ 0: a = "", b }] = ["", 1] : (string | number)[]
->[...{ 0: a = "", b }] : undefined[]
+>[...{ 0: a = "", b }] : unknown[]
 >...{ 0: a = "", b } : any
 >{ 0: a = "", b } : { 0?: string; b: number; }
 >0 : string

tests/baselines/reference/restElementWithAssignmentPattern4.types

@@ -11,7 +11,7 @@ var tuple: [string, number] = ["", 1];
 
 [...{ 0: a = "", b }] = tuple;
 >[...{ 0: a = "", b }] = tuple : [string, number]
->[...{ 0: a = "", b }] : undefined[]
+>[...{ 0: a = "", b }] : unknown[]
 >...{ 0: a = "", b } : any
 >{ 0: a = "", b } : { 0?: string; b: number; }
 >0 : string

tests/baselines/reference/restTupleElements1.errors.txt

@@ -4,26 +4,25 @@ tests/cases/conformance/types/tuple/restTupleElements1.ts(9,13): error TS2574: A
 tests/cases/conformance/types/tuple/restTupleElements1.ts(10,13): error TS2574: A rest element type must be an array type.
 tests/cases/conformance/types/tuple/restTupleElements1.ts(10,16): error TS8020: JSDoc types can only be used inside documentation comments.
 tests/cases/conformance/types/tuple/restTupleElements1.ts(23,31): error TS2344: Type 'number[]' does not satisfy the constraint '[number, ...number[]]'.
-  Property '0' is missing in type 'number[]' but required in type '[number, ...number[]]'.
+  Property '0' is optional in type 'number[]' but required in type '[number, ...number[]]'.
 tests/cases/conformance/types/tuple/restTupleElements1.ts(24,31): error TS2344: Type '[]' does not satisfy the constraint '[number, ...number[]]'.
-  Property '0' is missing in type '[]' but required in type '[number, ...number[]]'.
+  Source has 0 element(s) but target requires 1.
 tests/cases/conformance/types/tuple/restTupleElements1.ts(29,18): error TS2344: Type 'number[]' does not satisfy the constraint '[number]'.
-  Property '0' is missing in type 'number[]' but required in type '[number]'.
+  Target requires 1 element(s) but source may have fewer.
 tests/cases/conformance/types/tuple/restTupleElements1.ts(30,18): error TS2344: Type '[number, ...number[]]' does not satisfy the constraint '[number]'.
-  Types of property 'length' are incompatible.
-    Type 'number' is not assignable to type '1'.
+  Target allows only 1 element(s) but source may have more.
 tests/cases/conformance/types/tuple/restTupleElements1.ts(32,31): error TS2344: Type '[number, ...string[]]' does not satisfy the constraint '[number, ...number[]]'.
   Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/types/tuple/restTupleElements1.ts(33,31): error TS2344: Type '[string, ...number[]]' does not satisfy the constraint '[number, ...number[]]'.
   Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/types/tuple/restTupleElements1.ts(34,31): error TS2344: Type '[number, number, string]' does not satisfy the constraint '[number, ...number[]]'.
-  Property '2' is incompatible with rest element type.
+  Types of property '2' are incompatible.
     Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/types/tuple/restTupleElements1.ts(35,31): error TS2344: Type '[number, number, number, string]' does not satisfy the constraint '[number, ...number[]]'.
-  Property '3' is incompatible with rest element type.
+  Types of property '3' are incompatible.
     Type 'string' is not assignable to type 'number'.
 tests/cases/conformance/types/tuple/restTupleElements1.ts(59,4): error TS2345: Argument of type '[]' is not assignable to parameter of type '[unknown, ...unknown[]]'.
-  Property '0' is missing in type '[]' but required in type '[unknown, ...unknown[]]'.
+  Source has 0 element(s) but target requires 1.
 
 
 ==== tests/cases/conformance/types/tuple/restTupleElements1.ts (14 errors) ====
@@ -62,11 +61,11 @@ tests/cases/conformance/types/tuple/restTupleElements1.ts(59,4): error TS2345: A
     assign<[number, ...number[]], number[]>();  // Error
                                   ~~~~~~~~
 !!! error TS2344: Type 'number[]' does not satisfy the constraint '[number, ...number[]]'.
-!!! error TS2344:   Property '0' is missing in type 'number[]' but required in type '[number, ...number[]]'.
+!!! error TS2344:   Property '0' is optional in type 'number[]' but required in type '[number, ...number[]]'.
     assign<[number, ...number[]], []>();  // Error
                                   ~~
 !!! error TS2344: Type '[]' does not satisfy the constraint '[number, ...number[]]'.
-!!! error TS2344:   Property '0' is missing in type '[]' but required in type '[number, ...number[]]'.
+!!! error TS2344:   Source has 0 element(s) but target requires 1.
     assign<[number, ...number[]], [number]>();
     assign<[number, ...number[]], [number, number]>();
     assign<[number, ...number[]], [number, number, ...number[]]>();
@@ -74,12 +73,11 @@ tests/cases/conformance/types/tuple/restTupleElements1.ts(59,4): error TS2345: A
     assign<[number], [...number[]]>();  // Error
                      ~~~~~~~~~~~~~
 !!! error TS2344: Type 'number[]' does not satisfy the constraint '[number]'.
-!!! error TS2344:   Property '0' is missing in type 'number[]' but required in type '[number]'.
+!!! error TS2344:   Target requires 1 element(s) but source may have fewer.
     assign<[number], [number, ...number[]]>();  // Error
                      ~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2344: Type '[number, ...number[]]' does not satisfy the constraint '[number]'.
-!!! error TS2344:   Types of property 'length' are incompatible.
-!!! error TS2344:     Type 'number' is not assignable to type '1'.
+!!! error TS2344:   Target allows only 1 element(s) but source may have more.
     
     assign<[number, ...number[]], [number, ...string[]]>();  // Error
                                   ~~~~~~~~~~~~~~~~~~~~~
@@ -92,12 +90,12 @@ tests/cases/conformance/types/tuple/restTupleElements1.ts(59,4): error TS2345: A
     assign<[number, ...number[]], [number, number, string]>();  // Error
                                   ~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2344: Type '[number, number, string]' does not satisfy the constraint '[number, ...number[]]'.
-!!! error TS2344:   Property '2' is incompatible with rest element type.
+!!! error TS2344:   Types of property '2' are incompatible.
 !!! error TS2344:     Type 'string' is not assignable to type 'number'.
     assign<[number, ...number[]], [number, number, number, string]>();  // Error
                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2344: Type '[number, number, number, string]' does not satisfy the constraint '[number, ...number[]]'.
-!!! error TS2344:   Property '3' is incompatible with rest element type.
+!!! error TS2344:   Types of property '3' are incompatible.
 !!! error TS2344:     Type 'string' is not assignable to type 'number'.
     
     type T20 = [number, string, ...boolean[]];
@@ -125,7 +123,7 @@ tests/cases/conformance/types/tuple/restTupleElements1.ts(59,4): error TS2345: A
     f0([]);  // Error
        ~~
 !!! error TS2345: Argument of type '[]' is not assignable to parameter of type '[unknown, ...unknown[]]'.
-!!! error TS2345:   Property '0' is missing in type '[]' but required in type '[unknown, ...unknown[]]'.
+!!! error TS2345:   Source has 0 element(s) but target requires 1.
     f0([1]);
     f0([1, 2, 3]);
     f0([1, "hello", true]);

tests/baselines/reference/restTupleElements1.types

@@ -24,10 +24,10 @@ type T07 = [...string[], string];  // Error
 >T07 : T07
 
 type T08 = [...string];  // Error
->T08 : T08
+>T08 : any[]
 
 type T09 = [...string?];  // Error
->T09 : T09
+>T09 : any[]
 
 type T10 = [string, ...[...string[]]];
 >T10 : T10
@@ -107,7 +107,7 @@ type T21 = T20[0];
 >T21 : number
 
 type T22 = T20[0 | 1];
->T22 : string | number
+>T22 : T22
 
 type T23 = T20[0 | 1 | 2];
 >T23 : string | number | boolean

tests/baselines/reference/restTuplesFromContextualTypes.errors.txt

@@ -1,7 +1,8 @@
 tests/cases/conformance/types/rest/restTuplesFromContextualTypes.ts(56,7): error TS2345: Argument of type '(a: number, b: T[0], ...x: T[number][]) => void' is not assignable to parameter of type '(x: number, ...args: T) => void'.
   Types of parameters 'b' and 'args' are incompatible.
     Type 'T' is not assignable to type '[b: T[0], ...x: T[number][]]'.
-      Property '0' is missing in type 'any[]' but required in type '[b: T[0], ...x: T[number][]]'.
+      Type 'any[]' is not assignable to type '[b: T[0], ...x: T[number][]]'.
+        Property '0' is optional in type 'any[]' but required in type '[b: T[0], ...x: T[number][]]'.
 
 
 ==== tests/cases/conformance/types/rest/restTuplesFromContextualTypes.ts (1 errors) ====
@@ -65,7 +66,8 @@ tests/cases/conformance/types/rest/restTuplesFromContextualTypes.ts(56,7): error
 !!! error TS2345: Argument of type '(a: number, b: T[0], ...x: T[number][]) => void' is not assignable to parameter of type '(x: number, ...args: T) => void'.
 !!! error TS2345:   Types of parameters 'b' and 'args' are incompatible.
 !!! error TS2345:     Type 'T' is not assignable to type '[b: T[0], ...x: T[number][]]'.
-!!! error TS2345:       Property '0' is missing in type 'any[]' but required in type '[b: T[0], ...x: T[number][]]'.
+!!! error TS2345:       Type 'any[]' is not assignable to type '[b: T[0], ...x: T[number][]]'.
+!!! error TS2345:         Property '0' is optional in type 'any[]' but required in type '[b: T[0], ...x: T[number][]]'.
     }
     
     declare function f5<T extends any[], U>(f: (...args: T) => U): (...args: T) => U;

tests/baselines/reference/restTuplesFromContextualTypes.types

@@ -314,10 +314,10 @@ function f4<T extends any[]>(t: T) {
 
     (function(a, ...x){})(1, 2, ...t);
 >(function(a, ...x){})(1, 2, ...t) : void
->(function(a, ...x){}) : (a: number, x_0: number, ...x_1: any[]) => void
->function(a, ...x){} : (a: number, x_0: number, ...x_1: any[]) => void
+>(function(a, ...x){}) : (a: number, x_0: number, ...x_1: T) => void
+>function(a, ...x){} : (a: number, x_0: number, ...x_1: T) => void
 >a : number
->x : [number, ...any[]]
+>x : [number, ...T]
 >1 : 1
 >2 : 2
 >...t : any
@@ -332,8 +332,8 @@ function f4<T extends any[]>(t: T) {
     f((...x) => {});
 >f((...x) => {}) : void
 >f : (cb: (x: number, ...args: T) => void) => void
->(...x) => {} : (x: number, ...args: T[number][]) => void
->x : [x: number, ...args: T[number][]]
+>(...x) => {} : (x: number, ...args: T) => void
+>x : [x: number, ...args: T]
 
     f((a, ...x) => {});
 >f((a, ...x) => {}) : void

tests/baselines/reference/restTypeRetainsMappyness.errors.txt

@@ -1,15 +0,0 @@
-tests/cases/compiler/restTypeRetainsMappyness.ts(7,8): error TS2345: Argument of type 'Foo<T>[number][]' is not assignable to parameter of type 'Foo<T>'.
-
-
-==== tests/cases/compiler/restTypeRetainsMappyness.ts (1 errors) ====
-    type Foo<T extends any[]> = {
-        [P in keyof T]: T[P]
-    }
-    
-    function test<T extends any[]>(fn: (...args: Foo<T>) => void) {
-        const arr: Foo<T> = {} as any
-        fn(...arr) // Error: Argument of type 'any[]' is not assignable to parameter of type 'Foo<T>'
-           ~~~~~~
-!!! error TS2345: Argument of type 'Foo<T>[number][]' is not assignable to parameter of type 'Foo<T>'.
-    }
-    

tests/baselines/reference/spliceTuples.errors.txt

@@ -1,4 +1,5 @@
-tests/cases/compiler/spliceTuples.ts(23,1): error TS2741: Property '3' is missing in type '[number, string, boolean, ...boolean[]]' but required in type '[number, string, boolean, boolean, ...boolean[]]'.
+tests/cases/compiler/spliceTuples.ts(23,1): error TS2322: Type '[number, string, boolean, ...boolean[]]' is not assignable to type '[number, string, boolean, boolean, ...boolean[]]'.
+  Property '3' is optional in type '[number, string, boolean, ...boolean[]]' but required in type '[number, string, boolean, boolean, ...boolean[]]'.
 
 
 ==== tests/cases/compiler/spliceTuples.ts (1 errors) ====
@@ -26,5 +27,6 @@ tests/cases/compiler/spliceTuples.ts(23,1): error TS2741: Property '3' is missin
     let k6: [number, string, boolean, boolean, ...boolean[]];
     k6 = [1, ...sbb_];
     ~~
-!!! error TS2741: Property '3' is missing in type '[number, string, boolean, ...boolean[]]' but required in type '[number, string, boolean, boolean, ...boolean[]]'.
+!!! error TS2322: Type '[number, string, boolean, ...boolean[]]' is not assignable to type '[number, string, boolean, boolean, ...boolean[]]'.
+!!! error TS2322:   Property '3' is optional in type '[number, string, boolean, ...boolean[]]' but required in type '[number, string, boolean, boolean, ...boolean[]]'.
     

tests/baselines/reference/strictBindCallApply1.errors.txt

@@ -10,11 +10,10 @@ tests/cases/conformance/functions/strictBindCallApply1.ts(17,15): error TS2554:
 tests/cases/conformance/functions/strictBindCallApply1.ts(18,35): error TS2345: Argument of type 'number' is not assignable to parameter of type 'string'.
 tests/cases/conformance/functions/strictBindCallApply1.ts(19,44): error TS2554: Expected 3 arguments, but got 4.
 tests/cases/conformance/functions/strictBindCallApply1.ts(22,32): error TS2345: Argument of type '[number]' is not assignable to parameter of type '[a: number, b: string]'.
-  Property '1' is missing in type '[number]' but required in type '[a: number, b: string]'.
+  Source has 1 element(s) but target requires 2.
 tests/cases/conformance/functions/strictBindCallApply1.ts(23,37): error TS2322: Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/functions/strictBindCallApply1.ts(24,32): error TS2345: Argument of type '[number, string, number]' is not assignable to parameter of type '[a: number, b: string]'.
-  Types of property 'length' are incompatible.
-    Type '3' is not assignable to type '2'.
+  Source has 3 element(s) but target allows only 2.
 tests/cases/conformance/functions/strictBindCallApply1.ts(41,11): error TS2769: No overload matches this call.
   Overload 1 of 6, '(this: (this: C, arg0: 10, arg1: string) => string, thisArg: C, arg0: 10, arg1: string): () => string', gave the following error.
     Argument of type 'number' is not assignable to parameter of type 'string'.
@@ -36,11 +35,10 @@ tests/cases/conformance/functions/strictBindCallApply1.ts(49,29): error TS2345:
 tests/cases/conformance/functions/strictBindCallApply1.ts(50,38): error TS2554: Expected 3 arguments, but got 4.
 tests/cases/conformance/functions/strictBindCallApply1.ts(51,22): error TS2345: Argument of type 'undefined' is not assignable to parameter of type 'C'.
 tests/cases/conformance/functions/strictBindCallApply1.ts(54,26): error TS2345: Argument of type '[number]' is not assignable to parameter of type '[a: number, b: string]'.
-  Property '1' is missing in type '[number]' but required in type '[a: number, b: string]'.
+  Source has 1 element(s) but target requires 2.
 tests/cases/conformance/functions/strictBindCallApply1.ts(55,31): error TS2322: Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/functions/strictBindCallApply1.ts(56,26): error TS2345: Argument of type '[number, string, number]' is not assignable to parameter of type '[a: number, b: string]'.
-  Types of property 'length' are incompatible.
-    Type '3' is not assignable to type '2'.
+  Source has 3 element(s) but target allows only 2.
 tests/cases/conformance/functions/strictBindCallApply1.ts(57,23): error TS2345: Argument of type 'undefined' is not assignable to parameter of type 'C'.
 tests/cases/conformance/functions/strictBindCallApply1.ts(62,11): error TS2769: No overload matches this call.
   Overload 1 of 6, '(this: new (arg0: 10, arg1: string) => C, thisArg: any, arg0: 10, arg1: string): new () => C', gave the following error.
@@ -54,11 +52,10 @@ tests/cases/conformance/functions/strictBindCallApply1.ts(65,3): error TS2554: E
 tests/cases/conformance/functions/strictBindCallApply1.ts(66,15): error TS2345: Argument of type 'number' is not assignable to parameter of type 'string'.
 tests/cases/conformance/functions/strictBindCallApply1.ts(67,24): error TS2554: Expected 3 arguments, but got 4.
 tests/cases/conformance/functions/strictBindCallApply1.ts(70,12): error TS2345: Argument of type '[number]' is not assignable to parameter of type '[a: number, b: string]'.
-  Property '1' is missing in type '[number]' but required in type '[a: number, b: string]'.
+  Source has 1 element(s) but target requires 2.
 tests/cases/conformance/functions/strictBindCallApply1.ts(71,17): error TS2322: Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/functions/strictBindCallApply1.ts(72,12): error TS2345: Argument of type '[number, string, number]' is not assignable to parameter of type '[a: number, b: string]'.
-  Types of property 'length' are incompatible.
-    Type '3' is not assignable to type '2'.
+  Source has 3 element(s) but target allows only 2.
 
 
 ==== tests/cases/conformance/functions/strictBindCallApply1.ts (24 errors) ====
@@ -101,15 +98,14 @@ tests/cases/conformance/functions/strictBindCallApply1.ts(72,12): error TS2345:
     let a01 = foo.apply(undefined, [10]);  // Error
                                    ~~~~
 !!! error TS2345: Argument of type '[number]' is not assignable to parameter of type '[a: number, b: string]'.
-!!! error TS2345:   Property '1' is missing in type '[number]' but required in type '[a: number, b: string]'.
+!!! error TS2345:   Source has 1 element(s) but target requires 2.
     let a02 = foo.apply(undefined, [10, 20]);  // Error
                                         ~~
 !!! error TS2322: Type 'number' is not assignable to type 'string'.
     let a03 = foo.apply(undefined, [10, "hello", 30]);  // Error
                                    ~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, string, number]' is not assignable to parameter of type '[a: number, b: string]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '3' is not assignable to type '2'.
+!!! error TS2345:   Source has 3 element(s) but target allows only 2.
     
     class C {
         constructor(a: number, b: string) {}
@@ -168,15 +164,14 @@ tests/cases/conformance/functions/strictBindCallApply1.ts(72,12): error TS2345:
     let a11 = c.foo.apply(c, [10]);  // Error
                              ~~~~
 !!! error TS2345: Argument of type '[number]' is not assignable to parameter of type '[a: number, b: string]'.
-!!! error TS2345:   Property '1' is missing in type '[number]' but required in type '[a: number, b: string]'.
+!!! error TS2345:   Source has 1 element(s) but target requires 2.
     let a12 = c.foo.apply(c, [10, 20]);  // Error
                                   ~~
 !!! error TS2322: Type 'number' is not assignable to type 'string'.
     let a13 = c.foo.apply(c, [10, "hello", 30]);  // Error
                              ~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, string, number]' is not assignable to parameter of type '[a: number, b: string]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '3' is not assignable to type '2'.
+!!! error TS2345:   Source has 3 element(s) but target allows only 2.
     let a14 = c.foo.apply(undefined, [10, "hello"]);  // Error
                           ~~~~~~~~~
 !!! error TS2345: Argument of type 'undefined' is not assignable to parameter of type 'C'.
@@ -210,13 +205,12 @@ tests/cases/conformance/functions/strictBindCallApply1.ts(72,12): error TS2345:
     C.apply(c, [10]);  // Error
                ~~~~
 !!! error TS2345: Argument of type '[number]' is not assignable to parameter of type '[a: number, b: string]'.
-!!! error TS2345:   Property '1' is missing in type '[number]' but required in type '[a: number, b: string]'.
+!!! error TS2345:   Source has 1 element(s) but target requires 2.
     C.apply(c, [10, 20]);  // Error
                     ~~
 !!! error TS2322: Type 'number' is not assignable to type 'string'.
     C.apply(c, [10, "hello", 30]);  // Error
                ~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[number, string, number]' is not assignable to parameter of type '[a: number, b: string]'.
-!!! error TS2345:   Types of property 'length' are incompatible.
-!!! error TS2345:     Type '3' is not assignable to type '2'.
+!!! error TS2345:   Source has 3 element(s) but target allows only 2.
     

tests/baselines/reference/strictTupleLength.errors.txt

@@ -1,6 +1,7 @@
 tests/cases/conformance/types/tuple/strictTupleLength.ts(11,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 't1' must be of type '[number]', but here has type '[number, number]'.
 tests/cases/conformance/types/tuple/strictTupleLength.ts(12,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 't2' must be of type '[number, number]', but here has type '[number]'.
-tests/cases/conformance/types/tuple/strictTupleLength.ts(18,1): error TS2741: Property '0' is missing in type 'number[]' but required in type '[number]'.
+tests/cases/conformance/types/tuple/strictTupleLength.ts(18,1): error TS2322: Type 'number[]' is not assignable to type '[number]'.
+  Target requires 1 element(s) but source may have fewer.
 
 
 ==== tests/cases/conformance/types/tuple/strictTupleLength.ts (3 errors) ====
@@ -29,6 +30,7 @@ tests/cases/conformance/types/tuple/strictTupleLength.ts(18,1): error TS2741: Pr
     
     t1 = arr; // error with or without strict
     ~~
-!!! error TS2741: Property '0' is missing in type 'number[]' but required in type '[number]'.
+!!! error TS2322: Type 'number[]' is not assignable to type '[number]'.
+!!! error TS2322:   Target requires 1 element(s) but source may have fewer.
     arr = t1; // ok with or without strict
     

tests/baselines/reference/trailingCommasInBindingPatterns.types

@@ -14,7 +14,7 @@ let c, d;
 ([...c,] = []);
 >([...c,] = []) : undefined[]
 >[...c,] = [] : undefined[]
->[...c,] : undefined[]
+>[...c,] : any[]
 >...c : any
 >c : any
 >[] : undefined[]

tests/baselines/reference/tupleTypes.errors.txt

@@ -1,12 +1,13 @@
 tests/cases/compiler/tupleTypes.ts(11,12): error TS2493: Tuple type '[number, string]' of length '2' has no element at index '2'.
 tests/cases/compiler/tupleTypes.ts(12,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 't2' must be of type 'undefined', but here has type 'string | number'.
-tests/cases/compiler/tupleTypes.ts(14,1): error TS2739: Type '[]' is missing the following properties from type '[number, string]': 0, 1
-tests/cases/compiler/tupleTypes.ts(15,1): error TS2741: Property '1' is missing in type '[number]' but required in type '[number, string]'.
+tests/cases/compiler/tupleTypes.ts(14,1): error TS2322: Type '[]' is not assignable to type '[number, string]'.
+  Source has 0 element(s) but target requires 2.
+tests/cases/compiler/tupleTypes.ts(15,1): error TS2322: Type '[number]' is not assignable to type '[number, string]'.
+  Source has 1 element(s) but target requires 2.
 tests/cases/compiler/tupleTypes.ts(17,6): error TS2322: Type 'string' is not assignable to type 'number'.
 tests/cases/compiler/tupleTypes.ts(17,15): error TS2322: Type 'number' is not assignable to type 'string'.
 tests/cases/compiler/tupleTypes.ts(18,1): error TS2322: Type '[number, string, number]' is not assignable to type '[number, string]'.
-  Types of property 'length' are incompatible.
-    Type '3' is not assignable to type '2'.
+  Source has 3 element(s) but target allows only 2.
 tests/cases/compiler/tupleTypes.ts(35,14): error TS2493: Tuple type '[number, string]' of length '2' has no element at index '2'.
 tests/cases/compiler/tupleTypes.ts(36,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'tt2' must be of type 'undefined', but here has type 'string | number'.
 tests/cases/compiler/tupleTypes.ts(41,1): error TS2322: Type '[]' is not assignable to type '[number, string]'.
@@ -43,10 +44,12 @@ tests/cases/compiler/tupleTypes.ts(51,1): error TS2322: Type '[number, {}]' is n
     
     t = [];               // Error
     ~
-!!! error TS2739: Type '[]' is missing the following properties from type '[number, string]': 0, 1
+!!! error TS2322: Type '[]' is not assignable to type '[number, string]'.
+!!! error TS2322:   Source has 0 element(s) but target requires 2.
     t = [1];              // Error
     ~
-!!! error TS2741: Property '1' is missing in type '[number]' but required in type '[number, string]'.
+!!! error TS2322: Type '[number]' is not assignable to type '[number, string]'.
+!!! error TS2322:   Source has 1 element(s) but target requires 2.
     t = [1, "hello"];     // Ok
     t = ["hello", 1];     // Error
          ~~~~~~~
@@ -56,8 +59,7 @@ tests/cases/compiler/tupleTypes.ts(51,1): error TS2322: Type '[number, {}]' is n
     t = [1, "hello", 2];  // Error
     ~
 !!! error TS2322: Type '[number, string, number]' is not assignable to type '[number, string]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '3' is not assignable to type '2'.
+!!! error TS2322:   Source has 3 element(s) but target allows only 2.
     
     var tf: [string, (x: string) => number] = ["hello", x => x.length];
     

tests/baselines/reference/unionTypeFromArrayLiteral.errors.txt

@@ -1,6 +1,5 @@
 tests/cases/conformance/types/union/unionTypeFromArrayLiteral.ts(9,5): error TS2322: Type '[number, string, string]' is not assignable to type '[number, string]'.
-  Types of property 'length' are incompatible.
-    Type '3' is not assignable to type '2'.
+  Source has 3 element(s) but target allows only 2.
 
 
 ==== tests/cases/conformance/types/union/unionTypeFromArrayLiteral.ts (1 errors) ====
@@ -15,8 +14,7 @@ tests/cases/conformance/types/union/unionTypeFromArrayLiteral.ts(9,5): error TS2
     var arr4Tuple: [number, string] = [3, "three", "hello"]; // [number, string, string]
         ~~~~~~~~~
 !!! error TS2322: Type '[number, string, string]' is not assignable to type '[number, string]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '3' is not assignable to type '2'.
+!!! error TS2322:   Source has 3 element(s) but target allows only 2.
     var arrEmpty = [];
     var arr5Tuple: {
         0: string;

tests/baselines/reference/variadicTuples1.errors.txt

@@ -0,0 +1,361 @@
+tests/cases/conformance/types/tuple/variadicTuples1.ts(6,48): error TS1256: A rest element must be last in a tuple type.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(46,5): error TS2555: Expected at least 3 arguments, but got 2.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(47,17): error TS2345: Argument of type '45' is not assignable to parameter of type 'boolean'.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(125,9): error TS2344: Type 'V' does not satisfy the constraint 'unknown[]'.
+  The type 'readonly unknown[]' is 'readonly' and cannot be assigned to the mutable type 'unknown[]'.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(143,5): error TS2322: Type '[string, ...unknown[]]' is not assignable to type '[string, ...T]'.
+  Target requires 2 element(s) but source may have fewer.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(145,5): error TS2322: Type '[string, ...unknown[]]' is not assignable to type '[string, ...U]'.
+  Target requires 2 element(s) but source may have fewer.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(146,5): error TS2322: Type '[string, ...T]' is not assignable to type '[string, ...U]'.
+  Type 'T' is not assignable to type 'U'.
+    'T' is assignable to the constraint of type 'U', but 'U' could be instantiated with a different subtype of constraint 'string[]'.
+      Type 'string[]' is not assignable to type 'U'.
+        'U' could be instantiated with an arbitrary type which could be unrelated to 'string[]'.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(154,5): error TS2322: Type 'readonly [...T]' is not assignable to type 'T'.
+  'T' could be instantiated with an arbitrary type which could be unrelated to 'readonly [...T]'.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(156,5): error TS4104: The type 'readonly [...T]' is 'readonly' and cannot be assigned to the mutable type '[...T]'.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(163,5): error TS2322: Type 'readonly [...T]' is not assignable to type 'T'.
+  'readonly [...T]' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'readonly unknown[]'.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(164,5): error TS2322: Type 'T' is not assignable to type '[...T]'.
+  The type 'readonly unknown[]' is 'readonly' and cannot be assigned to the mutable type '[...T]'.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(165,5): error TS4104: The type 'readonly [...T]' is 'readonly' and cannot be assigned to the mutable type '[...T]'.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(297,14): error TS7019: Rest parameter 'x' implicitly has an 'any[]' type.
+
+
+==== tests/cases/conformance/types/tuple/variadicTuples1.ts (13 errors) ====
+    // Variadics in tuple types
+    
+    type TV0<T extends unknown[]> = [string, ...T];
+    type TV1<T extends unknown[]> = [string, ...T, number];
+    type TV2<T extends unknown[]> = [string, ...T, number, ...T];
+    type TV3<T extends unknown[]> = [string, ...T, ...number[], ...T];  // Error
+                                                   ~~~~~~~~~~~
+!!! error TS1256: A rest element must be last in a tuple type.
+    
+    // Normalization
+    
+    type TN1 = TV1<[boolean, string]>;
+    type TN2 = TV1<[]>;
+    type TN3 = TV1<[boolean?]>;
+    type TN4 = TV1<string[]>;
+    type TN5 = TV1<[boolean] | [symbol, symbol]>;
+    type TN6 = TV1<any>;
+    type TN7 = TV1<never>;
+    
+    // Variadics in array literals
+    
+    function tup2<T extends unknown[], U extends unknown[]>(t: [...T], u: [...U]) {
+        return [1, ...t, 2, ...u, 3] as const;
+    }
+    
+    const t2 = tup2(['hello'], [10, true]);
+    
+    function concat<T extends unknown[], U extends unknown[]>(t: [...T], u: [...U]): [...T, ...U] {
+        return [...t, ...u];
+    }
+    
+    declare const sa: string[];
+    
+    const tc1 = concat([], []);
+    const tc2 = concat(['hello'], [42]);
+    const tc3 = concat([1, 2, 3], sa);
+    const tc4 = concat(sa, [1, 2, 3]);  // Ideally would be [...string[], number, number, number]
+    
+    // Spread arguments
+    
+    declare function foo1(a: number, b: string, c: boolean, ...d: number[]): void;
+    
+    function foo2(t1: [number, string], t2: [boolean], a1: number[]) {
+        foo1(1, 'abc', true, 42, 43, 44);
+        foo1(...t1, true, 42, 43, 44);
+        foo1(...t1, ...t2, 42, 43, 44);
+        foo1(...t1, ...t2, ...a1);
+        foo1(...t1);  // Error
+        ~~~~~~~~~~~
+!!! error TS2555: Expected at least 3 arguments, but got 2.
+!!! related TS6210 tests/cases/conformance/types/tuple/variadicTuples1.ts:39:45: An argument for 'c' was not provided.
+        foo1(...t1, 45);  // Error
+                    ~~
+!!! error TS2345: Argument of type '45' is not assignable to parameter of type 'boolean'.
+    }
+    
+    declare function foo3<T extends unknown[]>(x: number, ...args: [...T, number]): T;
+    
+    function foo4<U extends unknown[]>(u: U) {
+        foo3(1, 2);
+        foo3(1, 'hello', true, 2);
+        foo3(1, ...u, 'hi', 2);
+        foo3(1);
+    }
+    
+    // Contextual typing of array literals
+    
+    declare function ft1<T extends unknown[]>(t: T): T;
+    declare function ft2<T extends unknown[]>(t: T): readonly [...T];
+    declare function ft3<T extends unknown[]>(t: [...T]): T;
+    declare function ft4<T extends unknown[]>(t: [...T]): readonly [...T];
+    
+    ft1(['hello', 42]);  // (string | number)[]
+    ft2(['hello', 42]);  // readonly (string | number)[]
+    ft3(['hello', 42]);  // [string, number]
+    ft4(['hello', 42]);  // readonly [string, number]
+    
+    // Indexing variadic tuple types
+    
+    function f0<T extends unknown[]>(t: [string, ...T], n: number) {
+        const a = t[0];  // string
+        const b = t[1];  // [string, ...T][1]
+        const c = t[2];  // [string, ...T][2]
+        const d = t[n];  // [string, ...T][number]
+    }
+    
+    function f1<T extends unknown[]>(t: [string, ...T, number], n: number) {
+        const a = t[0];  // string
+        const b = t[1];  // [string, ...T, number][1]
+        const c = t[2];  // [string, ...T, number][2]
+        const d = t[n];  // [string, ...T, number][number]
+    }
+    
+    // Destructuring variadic tuple types
+    
+    function f2<T extends unknown[]>(t: [string, ...T]) {
+        let [...ax] = t;  // [string, ...T]
+        let [b1, ...bx] = t;  // string, [...T]
+        let [c1, c2, ...cx] = t;  // string, [string, ...T][1], T[number][]
+    }
+    
+    function f3<T extends unknown[]>(t: [string, ...T, number]) {
+        let [...ax] = t;  // [string, ...T, number]
+        let [b1, ...bx] = t;  // string, [...T, number]
+        let [c1, c2, ...cx] = t;  // string, [string, ...T, number][1], (number | T[number])[]
+    }
+    
+    // Mapped types applied to variadic tuple types
+    
+    type Arrayify<T> = { [P in keyof T]: T[P][] };
+    
+    type TM1<U extends unknown[]> = Arrayify<readonly [string, number?, ...U, ...boolean[]]>;  // [string[], (number | undefined)[]?, Arrayify<U>, ...boolean[][]]
+    
+    type TP1<T extends unknown[]> = Partial<[string, ...T, number]>;  // [string?, Partial<T>, number?]
+    type TP2<T extends unknown[]> = Partial<[string, ...T, ...number[]]>;  // [string?, Partial<T>, ...(number | undefined)[]]
+    
+    // Reverse mapping through mapped type applied to variadic tuple type
+    
+    declare function fm1<T extends unknown[]>(t: Arrayify<[string, number, ...T]>): T;
+    
+    let tm1 = fm1([['abc'], [42], [true], ['def']]);  // [boolean, string]
+    
+    // Spread of readonly array-like infers mutable array-like
+    
+    declare function fx1<T extends unknown[]>(a: string, ...args: T): T;
+    
+    function gx1<U extends unknown[], V extends readonly unknown[]>(u: U, v: V) {
+        fx1('abc');  // []
+        fx1('abc', ...u);  // U
+        fx1('abc', ...v);  // [...V]
+        fx1<U>('abc', ...u);  // U
+        fx1<V>('abc', ...v);  // Error
+            ~
+!!! error TS2344: Type 'V' does not satisfy the constraint 'unknown[]'.
+!!! error TS2344:   The type 'readonly unknown[]' is 'readonly' and cannot be assigned to the mutable type 'unknown[]'.
+    }
+    
+    declare function fx2<T extends readonly unknown[]>(a: string, ...args: T): T;
+    
+    function gx2<U extends unknown[], V extends readonly unknown[]>(u: U, v: V) {
+        fx2('abc');  // []
+        fx2('abc', ...u);  // U
+        fx2('abc', ...v);  // [...V]
+        fx2<U>('abc', ...u);  // U
+        fx2<V>('abc', ...v);  // V
+    }
+    
+    // Relations involving variadic tuple types
+    
+    function f10<T extends string[], U extends T>(x: [string, ...unknown[]], y: [string, ...T], z: [string, ...U]) {
+        x = y;
+        x = z;
+        y = x;  // Error
+        ~
+!!! error TS2322: Type '[string, ...unknown[]]' is not assignable to type '[string, ...T]'.
+!!! error TS2322:   Target requires 2 element(s) but source may have fewer.
+        y = z;
+        z = x;  // Error
+        ~
+!!! error TS2322: Type '[string, ...unknown[]]' is not assignable to type '[string, ...U]'.
+!!! error TS2322:   Target requires 2 element(s) but source may have fewer.
+        z = y;  // Error
+        ~
+!!! error TS2322: Type '[string, ...T]' is not assignable to type '[string, ...U]'.
+!!! error TS2322:   Type 'T' is not assignable to type 'U'.
+!!! error TS2322:     'T' is assignable to the constraint of type 'U', but 'U' could be instantiated with a different subtype of constraint 'string[]'.
+!!! error TS2322:       Type 'string[]' is not assignable to type 'U'.
+!!! error TS2322:         'U' could be instantiated with an arbitrary type which could be unrelated to 'string[]'.
+    }
+    
+    // For a generic type T, [...T] is assignable to T, T is assignable to readonly [...T], and T is assignable
+    // to [...T] when T is constrained to a mutable array or tuple type.
+    
+    function f11<T extends unknown[]>(t: T, m: [...T], r: readonly [...T]) {
+        t = m;
+        t = r;  // Error
+        ~
+!!! error TS2322: Type 'readonly [...T]' is not assignable to type 'T'.
+!!! error TS2322:   'T' could be instantiated with an arbitrary type which could be unrelated to 'readonly [...T]'.
+        m = t;
+        m = r;  // Error
+        ~
+!!! error TS4104: The type 'readonly [...T]' is 'readonly' and cannot be assigned to the mutable type '[...T]'.
+        r = t;
+        r = m;
+    }
+    
+    function f12<T extends readonly unknown[]>(t: T, m: [...T], r: readonly [...T]) {
+        t = m;
+        t = r;  // Error
+        ~
+!!! error TS2322: Type 'readonly [...T]' is not assignable to type 'T'.
+!!! error TS2322:   'readonly [...T]' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'readonly unknown[]'.
+        m = t;  // Error
+        ~
+!!! error TS2322: Type 'T' is not assignable to type '[...T]'.
+!!! error TS2322:   The type 'readonly unknown[]' is 'readonly' and cannot be assigned to the mutable type '[...T]'.
+        m = r;  // Error
+        ~
+!!! error TS4104: The type 'readonly [...T]' is 'readonly' and cannot be assigned to the mutable type '[...T]'.
+        r = t;
+        r = m;
+    }
+    
+    // Inference between variadic tuple types
+    
+    type First<T extends readonly unknown[]> = T[0];
+    type DropFirst<T extends readonly unknown[]> = T extends readonly [any, ...infer U] ? U : [...T];
+    
+    type Last<T extends readonly unknown[]> = T extends readonly [...infer _, infer U] ? U : undefined;
+    type DropLast<T extends readonly unknown[]> = T extends readonly [...infer U, any] ? U : [...T];
+    
+    type T00 = First<[number, symbol, string]>;
+    type T01 = First<[symbol, string]>;
+    type T02 = First<[string]>;
+    type T03 = First<[number, symbol, ...string[]]>;
+    type T04 = First<[symbol, ...string[]]>;
+    type T05 = First<string[]>;
+    type T06 = First<[]>;
+    type T07 = First<any>;
+    type T08 = First<never>;
+    
+    type T10 = DropFirst<[number, symbol, string]>;
+    type T11 = DropFirst<[symbol, string]>;
+    type T12 = DropFirst<[string]>;
+    type T13 = DropFirst<[number, symbol, ...string[]]>;
+    type T14 = DropFirst<[symbol, ...string[]]>;
+    type T15 = DropFirst<string[]>;
+    type T16 = DropFirst<[]>;
+    type T17 = DropFirst<any>;
+    type T18 = DropFirst<never>;
+    
+    type T20 = Last<[number, symbol, string]>;
+    type T21 = Last<[symbol, string]>;
+    type T22 = Last<[string]>;
+    type T23 = Last<[number, symbol, ...string[]]>;
+    type T24 = Last<[symbol, ...string[]]>;
+    type T25 = Last<string[]>;
+    type T26 = Last<[]>;  // unknown[], maybe should be []
+    type T27 = Last<any>;  // unknown, maybe should be any
+    type T28 = Last<never>;
+    
+    type T30 = DropLast<[number, symbol, string]>;
+    type T31 = DropLast<[symbol, string]>;
+    type T32 = DropLast<[string]>;
+    type T33 = DropLast<[number, symbol, ...string[]]>;
+    type T34 = DropLast<[symbol, ...string[]]>;
+    type T35 = DropLast<string[]>;
+    type T36 = DropLast<[]>;  // unknown[], maybe should be []
+    type T37 = DropLast<any>;
+    type T38 = DropLast<never>;
+    
+    type R00 = First<readonly [number, symbol, string]>;
+    type R01 = First<readonly [symbol, string]>;
+    type R02 = First<readonly [string]>;
+    type R03 = First<readonly [number, symbol, ...string[]]>;
+    type R04 = First<readonly [symbol, ...string[]]>;
+    type R05 = First<readonly string[]>;
+    type R06 = First<readonly []>;
+    
+    type R10 = DropFirst<readonly [number, symbol, string]>;
+    type R11 = DropFirst<readonly [symbol, string]>;
+    type R12 = DropFirst<readonly [string]>;
+    type R13 = DropFirst<readonly [number, symbol, ...string[]]>;
+    type R14 = DropFirst<readonly [symbol, ...string[]]>;
+    type R15 = DropFirst<readonly string[]>;
+    type R16 = DropFirst<readonly []>;
+    
+    type R20 = Last<readonly [number, symbol, string]>;
+    type R21 = Last<readonly [symbol, string]>;
+    type R22 = Last<readonly [string]>;
+    type R23 = Last<readonly [number, symbol, ...string[]]>;
+    type R24 = Last<readonly [symbol, ...string[]]>;
+    type R25 = Last<readonly string[]>;
+    type R26 = Last<readonly []>;
+    
+    type R30 = DropLast<readonly [number, symbol, string]>;
+    type R31 = DropLast<readonly [symbol, string]>;
+    type R32 = DropLast<readonly [string]>;
+    type R33 = DropLast<readonly [number, symbol, ...string[]]>;
+    type R34 = DropLast<readonly [symbol, ...string[]]>;
+    type R35 = DropLast<readonly string[]>;
+    type R36 = DropLast<readonly []>;
+    
+    // Inference to [...T, ...U] with implied arity for T
+    
+    function curry<T extends unknown[], U extends unknown[], R>(f: (...args: [...T, ...U]) => R, ...a: T) {
+        return (...b: U) => f(...a, ...b);
+    }
+    
+    const fn1 = (a: number, b: string, c: boolean, d: string[]) => 0;
+    
+    const c0 = curry(fn1);  // (a: number, b: string, c: boolean, d: string[]) => number
+    const c1 = curry(fn1, 1);  // (b: string, c: boolean, d: string[]) => number
+    const c2 = curry(fn1, 1, 'abc');  // (c: boolean, d: string[]) => number
+    const c3 = curry(fn1, 1, 'abc', true);  // (d: string[]) => number
+    const c4 = curry(fn1, 1, 'abc', true, ['x', 'y']);  // () => number
+    
+    const fn2 = (x: number, b: boolean, ...args: string[]) => 0;
+    
+    const c10 = curry(fn2);  // (x: number, b: boolean, ...args: string[]) => number
+    const c11 = curry(fn2, 1);  // (b: boolean, ...args: string[]) => number
+    const c12 = curry(fn2, 1, true);  // (...args: string[]) => number
+    const c13 = curry(fn2, 1, true, 'abc', 'def');  // (...args: string[]) => number
+    
+    const fn3 = (...args: string[]) => 0;
+    
+    const c20 = curry(fn3);  // (...args: string[]) => number
+    const c21 = curry(fn3, 'abc', 'def');  // (...args: string[]) => number
+    const c22 = curry(fn3, ...sa);  // (...args: string[]) => number
+    
+    // No inference to [...T, ...U] when there is no implied arity
+    
+    function curry2<T extends unknown[], U extends unknown[], R>(f: (...args: [...T, ...U]) => R, t: [...T], u: [...U]) {
+        return f(...t, ...u);
+    }
+    
+    declare function fn10(a: string, b: number, c: boolean): string[];
+    
+    curry2(fn10, ['hello', 42], [true]);
+    curry2(fn10, ['hello'], [42, true]);
+    
+    // Last argument is contextually typed
+    
+    declare function call<T extends unknown[], R>(...args: [...T, (...args: T) => R]): [T, R];
+    
+    call('hello', 32, (a, b) => 42);
+    
+    // Would be nice to infer [...string[], (...args: string[]) => number] here
+    // Requires [starting-fixed-part, ...rest-part, ending-fixed-part] tuple structure
+    
+    call(...sa, (...x) => 42);
+                 ~~~~
+!!! error TS7019: Rest parameter 'x' implicitly has an 'any[]' type.
+    

tests/baselines/reference/variadicTuples1.js

@@ -0,0 +1,599 @@
+//// [variadicTuples1.ts]
+// Variadics in tuple types
+
+type TV0<T extends unknown[]> = [string, ...T];
+type TV1<T extends unknown[]> = [string, ...T, number];
+type TV2<T extends unknown[]> = [string, ...T, number, ...T];
+type TV3<T extends unknown[]> = [string, ...T, ...number[], ...T];  // Error
+
+// Normalization
+
+type TN1 = TV1<[boolean, string]>;
+type TN2 = TV1<[]>;
+type TN3 = TV1<[boolean?]>;
+type TN4 = TV1<string[]>;
+type TN5 = TV1<[boolean] | [symbol, symbol]>;
+type TN6 = TV1<any>;
+type TN7 = TV1<never>;
+
+// Variadics in array literals
+
+function tup2<T extends unknown[], U extends unknown[]>(t: [...T], u: [...U]) {
+    return [1, ...t, 2, ...u, 3] as const;
+}
+
+const t2 = tup2(['hello'], [10, true]);
+
+function concat<T extends unknown[], U extends unknown[]>(t: [...T], u: [...U]): [...T, ...U] {
+    return [...t, ...u];
+}
+
+declare const sa: string[];
+
+const tc1 = concat([], []);
+const tc2 = concat(['hello'], [42]);
+const tc3 = concat([1, 2, 3], sa);
+const tc4 = concat(sa, [1, 2, 3]);  // Ideally would be [...string[], number, number, number]
+
+// Spread arguments
+
+declare function foo1(a: number, b: string, c: boolean, ...d: number[]): void;
+
+function foo2(t1: [number, string], t2: [boolean], a1: number[]) {
+    foo1(1, 'abc', true, 42, 43, 44);
+    foo1(...t1, true, 42, 43, 44);
+    foo1(...t1, ...t2, 42, 43, 44);
+    foo1(...t1, ...t2, ...a1);
+    foo1(...t1);  // Error
+    foo1(...t1, 45);  // Error
+}
+
+declare function foo3<T extends unknown[]>(x: number, ...args: [...T, number]): T;
+
+function foo4<U extends unknown[]>(u: U) {
+    foo3(1, 2);
+    foo3(1, 'hello', true, 2);
+    foo3(1, ...u, 'hi', 2);
+    foo3(1);
+}
+
+// Contextual typing of array literals
+
+declare function ft1<T extends unknown[]>(t: T): T;
+declare function ft2<T extends unknown[]>(t: T): readonly [...T];
+declare function ft3<T extends unknown[]>(t: [...T]): T;
+declare function ft4<T extends unknown[]>(t: [...T]): readonly [...T];
+
+ft1(['hello', 42]);  // (string | number)[]
+ft2(['hello', 42]);  // readonly (string | number)[]
+ft3(['hello', 42]);  // [string, number]
+ft4(['hello', 42]);  // readonly [string, number]
+
+// Indexing variadic tuple types
+
+function f0<T extends unknown[]>(t: [string, ...T], n: number) {
+    const a = t[0];  // string
+    const b = t[1];  // [string, ...T][1]
+    const c = t[2];  // [string, ...T][2]
+    const d = t[n];  // [string, ...T][number]
+}
+
+function f1<T extends unknown[]>(t: [string, ...T, number], n: number) {
+    const a = t[0];  // string
+    const b = t[1];  // [string, ...T, number][1]
+    const c = t[2];  // [string, ...T, number][2]
+    const d = t[n];  // [string, ...T, number][number]
+}
+
+// Destructuring variadic tuple types
+
+function f2<T extends unknown[]>(t: [string, ...T]) {
+    let [...ax] = t;  // [string, ...T]
+    let [b1, ...bx] = t;  // string, [...T]
+    let [c1, c2, ...cx] = t;  // string, [string, ...T][1], T[number][]
+}
+
+function f3<T extends unknown[]>(t: [string, ...T, number]) {
+    let [...ax] = t;  // [string, ...T, number]
+    let [b1, ...bx] = t;  // string, [...T, number]
+    let [c1, c2, ...cx] = t;  // string, [string, ...T, number][1], (number | T[number])[]
+}
+
+// Mapped types applied to variadic tuple types
+
+type Arrayify<T> = { [P in keyof T]: T[P][] };
+
+type TM1<U extends unknown[]> = Arrayify<readonly [string, number?, ...U, ...boolean[]]>;  // [string[], (number | undefined)[]?, Arrayify<U>, ...boolean[][]]
+
+type TP1<T extends unknown[]> = Partial<[string, ...T, number]>;  // [string?, Partial<T>, number?]
+type TP2<T extends unknown[]> = Partial<[string, ...T, ...number[]]>;  // [string?, Partial<T>, ...(number | undefined)[]]
+
+// Reverse mapping through mapped type applied to variadic tuple type
+
+declare function fm1<T extends unknown[]>(t: Arrayify<[string, number, ...T]>): T;
+
+let tm1 = fm1([['abc'], [42], [true], ['def']]);  // [boolean, string]
+
+// Spread of readonly array-like infers mutable array-like
+
+declare function fx1<T extends unknown[]>(a: string, ...args: T): T;
+
+function gx1<U extends unknown[], V extends readonly unknown[]>(u: U, v: V) {
+    fx1('abc');  // []
+    fx1('abc', ...u);  // U
+    fx1('abc', ...v);  // [...V]
+    fx1<U>('abc', ...u);  // U
+    fx1<V>('abc', ...v);  // Error
+}
+
+declare function fx2<T extends readonly unknown[]>(a: string, ...args: T): T;
+
+function gx2<U extends unknown[], V extends readonly unknown[]>(u: U, v: V) {
+    fx2('abc');  // []
+    fx2('abc', ...u);  // U
+    fx2('abc', ...v);  // [...V]
+    fx2<U>('abc', ...u);  // U
+    fx2<V>('abc', ...v);  // V
+}
+
+// Relations involving variadic tuple types
+
+function f10<T extends string[], U extends T>(x: [string, ...unknown[]], y: [string, ...T], z: [string, ...U]) {
+    x = y;
+    x = z;
+    y = x;  // Error
+    y = z;
+    z = x;  // Error
+    z = y;  // Error
+}
+
+// For a generic type T, [...T] is assignable to T, T is assignable to readonly [...T], and T is assignable
+// to [...T] when T is constrained to a mutable array or tuple type.
+
+function f11<T extends unknown[]>(t: T, m: [...T], r: readonly [...T]) {
+    t = m;
+    t = r;  // Error
+    m = t;
+    m = r;  // Error
+    r = t;
+    r = m;
+}
+
+function f12<T extends readonly unknown[]>(t: T, m: [...T], r: readonly [...T]) {
+    t = m;
+    t = r;  // Error
+    m = t;  // Error
+    m = r;  // Error
+    r = t;
+    r = m;
+}
+
+// Inference between variadic tuple types
+
+type First<T extends readonly unknown[]> = T[0];
+type DropFirst<T extends readonly unknown[]> = T extends readonly [any, ...infer U] ? U : [...T];
+
+type Last<T extends readonly unknown[]> = T extends readonly [...infer _, infer U] ? U : undefined;
+type DropLast<T extends readonly unknown[]> = T extends readonly [...infer U, any] ? U : [...T];
+
+type T00 = First<[number, symbol, string]>;
+type T01 = First<[symbol, string]>;
+type T02 = First<[string]>;
+type T03 = First<[number, symbol, ...string[]]>;
+type T04 = First<[symbol, ...string[]]>;
+type T05 = First<string[]>;
+type T06 = First<[]>;
+type T07 = First<any>;
+type T08 = First<never>;
+
+type T10 = DropFirst<[number, symbol, string]>;
+type T11 = DropFirst<[symbol, string]>;
+type T12 = DropFirst<[string]>;
+type T13 = DropFirst<[number, symbol, ...string[]]>;
+type T14 = DropFirst<[symbol, ...string[]]>;
+type T15 = DropFirst<string[]>;
+type T16 = DropFirst<[]>;
+type T17 = DropFirst<any>;
+type T18 = DropFirst<never>;
+
+type T20 = Last<[number, symbol, string]>;
+type T21 = Last<[symbol, string]>;
+type T22 = Last<[string]>;
+type T23 = Last<[number, symbol, ...string[]]>;
+type T24 = Last<[symbol, ...string[]]>;
+type T25 = Last<string[]>;
+type T26 = Last<[]>;  // unknown[], maybe should be []
+type T27 = Last<any>;  // unknown, maybe should be any
+type T28 = Last<never>;
+
+type T30 = DropLast<[number, symbol, string]>;
+type T31 = DropLast<[symbol, string]>;
+type T32 = DropLast<[string]>;
+type T33 = DropLast<[number, symbol, ...string[]]>;
+type T34 = DropLast<[symbol, ...string[]]>;
+type T35 = DropLast<string[]>;
+type T36 = DropLast<[]>;  // unknown[], maybe should be []
+type T37 = DropLast<any>;
+type T38 = DropLast<never>;
+
+type R00 = First<readonly [number, symbol, string]>;
+type R01 = First<readonly [symbol, string]>;
+type R02 = First<readonly [string]>;
+type R03 = First<readonly [number, symbol, ...string[]]>;
+type R04 = First<readonly [symbol, ...string[]]>;
+type R05 = First<readonly string[]>;
+type R06 = First<readonly []>;
+
+type R10 = DropFirst<readonly [number, symbol, string]>;
+type R11 = DropFirst<readonly [symbol, string]>;
+type R12 = DropFirst<readonly [string]>;
+type R13 = DropFirst<readonly [number, symbol, ...string[]]>;
+type R14 = DropFirst<readonly [symbol, ...string[]]>;
+type R15 = DropFirst<readonly string[]>;
+type R16 = DropFirst<readonly []>;
+
+type R20 = Last<readonly [number, symbol, string]>;
+type R21 = Last<readonly [symbol, string]>;
+type R22 = Last<readonly [string]>;
+type R23 = Last<readonly [number, symbol, ...string[]]>;
+type R24 = Last<readonly [symbol, ...string[]]>;
+type R25 = Last<readonly string[]>;
+type R26 = Last<readonly []>;
+
+type R30 = DropLast<readonly [number, symbol, string]>;
+type R31 = DropLast<readonly [symbol, string]>;
+type R32 = DropLast<readonly [string]>;
+type R33 = DropLast<readonly [number, symbol, ...string[]]>;
+type R34 = DropLast<readonly [symbol, ...string[]]>;
+type R35 = DropLast<readonly string[]>;
+type R36 = DropLast<readonly []>;
+
+// Inference to [...T, ...U] with implied arity for T
+
+function curry<T extends unknown[], U extends unknown[], R>(f: (...args: [...T, ...U]) => R, ...a: T) {
+    return (...b: U) => f(...a, ...b);
+}
+
+const fn1 = (a: number, b: string, c: boolean, d: string[]) => 0;
+
+const c0 = curry(fn1);  // (a: number, b: string, c: boolean, d: string[]) => number
+const c1 = curry(fn1, 1);  // (b: string, c: boolean, d: string[]) => number
+const c2 = curry(fn1, 1, 'abc');  // (c: boolean, d: string[]) => number
+const c3 = curry(fn1, 1, 'abc', true);  // (d: string[]) => number
+const c4 = curry(fn1, 1, 'abc', true, ['x', 'y']);  // () => number
+
+const fn2 = (x: number, b: boolean, ...args: string[]) => 0;
+
+const c10 = curry(fn2);  // (x: number, b: boolean, ...args: string[]) => number
+const c11 = curry(fn2, 1);  // (b: boolean, ...args: string[]) => number
+const c12 = curry(fn2, 1, true);  // (...args: string[]) => number
+const c13 = curry(fn2, 1, true, 'abc', 'def');  // (...args: string[]) => number
+
+const fn3 = (...args: string[]) => 0;
+
+const c20 = curry(fn3);  // (...args: string[]) => number
+const c21 = curry(fn3, 'abc', 'def');  // (...args: string[]) => number
+const c22 = curry(fn3, ...sa);  // (...args: string[]) => number
+
+// No inference to [...T, ...U] when there is no implied arity
+
+function curry2<T extends unknown[], U extends unknown[], R>(f: (...args: [...T, ...U]) => R, t: [...T], u: [...U]) {
+    return f(...t, ...u);
+}
+
+declare function fn10(a: string, b: number, c: boolean): string[];
+
+curry2(fn10, ['hello', 42], [true]);
+curry2(fn10, ['hello'], [42, true]);
+
+// Last argument is contextually typed
+
+declare function call<T extends unknown[], R>(...args: [...T, (...args: T) => R]): [T, R];
+
+call('hello', 32, (a, b) => 42);
+
+// Would be nice to infer [...string[], (...args: string[]) => number] here
+// Requires [starting-fixed-part, ...rest-part, ending-fixed-part] tuple structure
+
+call(...sa, (...x) => 42);
+
+
+//// [variadicTuples1.js]
+"use strict";
+// Variadics in tuple types
+var __spreadArrays = (this && this.__spreadArrays) || function () {
+    for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
+    for (var r = Array(s), k = 0, i = 0; i < il; i++)
+        for (var a = arguments[i], j = 0, jl = a.length; j < jl; j++, k++)
+            r[k] = a[j];
+    return r;
+};
+// Variadics in array literals
+function tup2(t, u) {
+    return __spreadArrays([1], t, [2], u, [3]);
+}
+var t2 = tup2(['hello'], [10, true]);
+function concat(t, u) {
+    return __spreadArrays(t, u);
+}
+var tc1 = concat([], []);
+var tc2 = concat(['hello'], [42]);
+var tc3 = concat([1, 2, 3], sa);
+var tc4 = concat(sa, [1, 2, 3]); // Ideally would be [...string[], number, number, number]
+function foo2(t1, t2, a1) {
+    foo1(1, 'abc', true, 42, 43, 44);
+    foo1.apply(void 0, __spreadArrays(t1, [true, 42, 43, 44]));
+    foo1.apply(void 0, __spreadArrays(t1, t2, [42, 43, 44]));
+    foo1.apply(void 0, __spreadArrays(t1, t2, a1));
+    foo1.apply(void 0, t1); // Error
+    foo1.apply(void 0, __spreadArrays(t1, [45])); // Error
+}
+function foo4(u) {
+    foo3(1, 2);
+    foo3(1, 'hello', true, 2);
+    foo3.apply(void 0, __spreadArrays([1], u, ['hi', 2]));
+    foo3(1);
+}
+ft1(['hello', 42]); // (string | number)[]
+ft2(['hello', 42]); // readonly (string | number)[]
+ft3(['hello', 42]); // [string, number]
+ft4(['hello', 42]); // readonly [string, number]
+// Indexing variadic tuple types
+function f0(t, n) {
+    var a = t[0]; // string
+    var b = t[1]; // [string, ...T][1]
+    var c = t[2]; // [string, ...T][2]
+    var d = t[n]; // [string, ...T][number]
+}
+function f1(t, n) {
+    var a = t[0]; // string
+    var b = t[1]; // [string, ...T, number][1]
+    var c = t[2]; // [string, ...T, number][2]
+    var d = t[n]; // [string, ...T, number][number]
+}
+// Destructuring variadic tuple types
+function f2(t) {
+    var ax = t.slice(0); // [string, ...T]
+    var b1 = t[0], bx = t.slice(1); // string, [...T]
+    var c1 = t[0], c2 = t[1], cx = t.slice(2); // string, [string, ...T][1], T[number][]
+}
+function f3(t) {
+    var ax = t.slice(0); // [string, ...T, number]
+    var b1 = t[0], bx = t.slice(1); // string, [...T, number]
+    var c1 = t[0], c2 = t[1], cx = t.slice(2); // string, [string, ...T, number][1], (number | T[number])[]
+}
+var tm1 = fm1([['abc'], [42], [true], ['def']]); // [boolean, string]
+function gx1(u, v) {
+    fx1('abc'); // []
+    fx1.apply(void 0, __spreadArrays(['abc'], u)); // U
+    fx1.apply(void 0, __spreadArrays(['abc'], v)); // [...V]
+    fx1.apply(void 0, __spreadArrays(['abc'], u)); // U
+    fx1.apply(void 0, __spreadArrays(['abc'], v)); // Error
+}
+function gx2(u, v) {
+    fx2('abc'); // []
+    fx2.apply(void 0, __spreadArrays(['abc'], u)); // U
+    fx2.apply(void 0, __spreadArrays(['abc'], v)); // [...V]
+    fx2.apply(void 0, __spreadArrays(['abc'], u)); // U
+    fx2.apply(void 0, __spreadArrays(['abc'], v)); // V
+}
+// Relations involving variadic tuple types
+function f10(x, y, z) {
+    x = y;
+    x = z;
+    y = x; // Error
+    y = z;
+    z = x; // Error
+    z = y; // Error
+}
+// For a generic type T, [...T] is assignable to T, T is assignable to readonly [...T], and T is assignable
+// to [...T] when T is constrained to a mutable array or tuple type.
+function f11(t, m, r) {
+    t = m;
+    t = r; // Error
+    m = t;
+    m = r; // Error
+    r = t;
+    r = m;
+}
+function f12(t, m, r) {
+    t = m;
+    t = r; // Error
+    m = t; // Error
+    m = r; // Error
+    r = t;
+    r = m;
+}
+// Inference to [...T, ...U] with implied arity for T
+function curry(f) {
+    var a = [];
+    for (var _i = 1; _i < arguments.length; _i++) {
+        a[_i - 1] = arguments[_i];
+    }
+    return function () {
+        var b = [];
+        for (var _i = 0; _i < arguments.length; _i++) {
+            b[_i] = arguments[_i];
+        }
+        return f.apply(void 0, __spreadArrays(a, b));
+    };
+}
+var fn1 = function (a, b, c, d) { return 0; };
+var c0 = curry(fn1); // (a: number, b: string, c: boolean, d: string[]) => number
+var c1 = curry(fn1, 1); // (b: string, c: boolean, d: string[]) => number
+var c2 = curry(fn1, 1, 'abc'); // (c: boolean, d: string[]) => number
+var c3 = curry(fn1, 1, 'abc', true); // (d: string[]) => number
+var c4 = curry(fn1, 1, 'abc', true, ['x', 'y']); // () => number
+var fn2 = function (x, b) {
+    var args = [];
+    for (var _i = 2; _i < arguments.length; _i++) {
+        args[_i - 2] = arguments[_i];
+    }
+    return 0;
+};
+var c10 = curry(fn2); // (x: number, b: boolean, ...args: string[]) => number
+var c11 = curry(fn2, 1); // (b: boolean, ...args: string[]) => number
+var c12 = curry(fn2, 1, true); // (...args: string[]) => number
+var c13 = curry(fn2, 1, true, 'abc', 'def'); // (...args: string[]) => number
+var fn3 = function () {
+    var args = [];
+    for (var _i = 0; _i < arguments.length; _i++) {
+        args[_i] = arguments[_i];
+    }
+    return 0;
+};
+var c20 = curry(fn3); // (...args: string[]) => number
+var c21 = curry(fn3, 'abc', 'def'); // (...args: string[]) => number
+var c22 = curry.apply(void 0, __spreadArrays([fn3], sa)); // (...args: string[]) => number
+// No inference to [...T, ...U] when there is no implied arity
+function curry2(f, t, u) {
+    return f.apply(void 0, __spreadArrays(t, u));
+}
+curry2(fn10, ['hello', 42], [true]);
+curry2(fn10, ['hello'], [42, true]);
+call('hello', 32, function (a, b) { return 42; });
+// Would be nice to infer [...string[], (...args: string[]) => number] here
+// Requires [starting-fixed-part, ...rest-part, ending-fixed-part] tuple structure
+call.apply(void 0, __spreadArrays(sa, [function () {
+        var x = [];
+        for (var _i = 0; _i < arguments.length; _i++) {
+            x[_i] = arguments[_i];
+        }
+        return 42;
+    }]));
+
+
+//// [variadicTuples1.d.ts]
+declare type TV0<T extends unknown[]> = [string, ...T];
+declare type TV1<T extends unknown[]> = [string, ...T, number];
+declare type TV2<T extends unknown[]> = [string, ...T, number, ...T];
+declare type TV3<T extends unknown[]> = [string, ...T, ...number[], ...T];
+declare type TN1 = TV1<[boolean, string]>;
+declare type TN2 = TV1<[]>;
+declare type TN3 = TV1<[boolean?]>;
+declare type TN4 = TV1<string[]>;
+declare type TN5 = TV1<[boolean] | [symbol, symbol]>;
+declare type TN6 = TV1<any>;
+declare type TN7 = TV1<never>;
+declare function tup2<T extends unknown[], U extends unknown[]>(t: [...T], u: [...U]): readonly [1, ...T, 2, ...U, 3];
+declare const t2: readonly [1, string, 2, number, boolean, 3];
+declare function concat<T extends unknown[], U extends unknown[]>(t: [...T], u: [...U]): [...T, ...U];
+declare const sa: string[];
+declare const tc1: [];
+declare const tc2: [string, number];
+declare const tc3: [number, number, number, ...string[]];
+declare const tc4: (string | number)[];
+declare function foo1(a: number, b: string, c: boolean, ...d: number[]): void;
+declare function foo2(t1: [number, string], t2: [boolean], a1: number[]): void;
+declare function foo3<T extends unknown[]>(x: number, ...args: [...T, number]): T;
+declare function foo4<U extends unknown[]>(u: U): void;
+declare function ft1<T extends unknown[]>(t: T): T;
+declare function ft2<T extends unknown[]>(t: T): readonly [...T];
+declare function ft3<T extends unknown[]>(t: [...T]): T;
+declare function ft4<T extends unknown[]>(t: [...T]): readonly [...T];
+declare function f0<T extends unknown[]>(t: [string, ...T], n: number): void;
+declare function f1<T extends unknown[]>(t: [string, ...T, number], n: number): void;
+declare function f2<T extends unknown[]>(t: [string, ...T]): void;
+declare function f3<T extends unknown[]>(t: [string, ...T, number]): void;
+declare type Arrayify<T> = {
+    [P in keyof T]: T[P][];
+};
+declare type TM1<U extends unknown[]> = Arrayify<readonly [string, number?, ...U, ...boolean[]]>;
+declare type TP1<T extends unknown[]> = Partial<[string, ...T, number]>;
+declare type TP2<T extends unknown[]> = Partial<[string, ...T, ...number[]]>;
+declare function fm1<T extends unknown[]>(t: Arrayify<[string, number, ...T]>): T;
+declare let tm1: [boolean, string];
+declare function fx1<T extends unknown[]>(a: string, ...args: T): T;
+declare function gx1<U extends unknown[], V extends readonly unknown[]>(u: U, v: V): void;
+declare function fx2<T extends readonly unknown[]>(a: string, ...args: T): T;
+declare function gx2<U extends unknown[], V extends readonly unknown[]>(u: U, v: V): void;
+declare function f10<T extends string[], U extends T>(x: [string, ...unknown[]], y: [string, ...T], z: [string, ...U]): void;
+declare function f11<T extends unknown[]>(t: T, m: [...T], r: readonly [...T]): void;
+declare function f12<T extends readonly unknown[]>(t: T, m: [...T], r: readonly [...T]): void;
+declare type First<T extends readonly unknown[]> = T[0];
+declare type DropFirst<T extends readonly unknown[]> = T extends readonly [any, ...infer U] ? U : [...T];
+declare type Last<T extends readonly unknown[]> = T extends readonly [...infer _, infer U] ? U : undefined;
+declare type DropLast<T extends readonly unknown[]> = T extends readonly [...infer U, any] ? U : [...T];
+declare type T00 = First<[number, symbol, string]>;
+declare type T01 = First<[symbol, string]>;
+declare type T02 = First<[string]>;
+declare type T03 = First<[number, symbol, ...string[]]>;
+declare type T04 = First<[symbol, ...string[]]>;
+declare type T05 = First<string[]>;
+declare type T06 = First<[]>;
+declare type T07 = First<any>;
+declare type T08 = First<never>;
+declare type T10 = DropFirst<[number, symbol, string]>;
+declare type T11 = DropFirst<[symbol, string]>;
+declare type T12 = DropFirst<[string]>;
+declare type T13 = DropFirst<[number, symbol, ...string[]]>;
+declare type T14 = DropFirst<[symbol, ...string[]]>;
+declare type T15 = DropFirst<string[]>;
+declare type T16 = DropFirst<[]>;
+declare type T17 = DropFirst<any>;
+declare type T18 = DropFirst<never>;
+declare type T20 = Last<[number, symbol, string]>;
+declare type T21 = Last<[symbol, string]>;
+declare type T22 = Last<[string]>;
+declare type T23 = Last<[number, symbol, ...string[]]>;
+declare type T24 = Last<[symbol, ...string[]]>;
+declare type T25 = Last<string[]>;
+declare type T26 = Last<[]>;
+declare type T27 = Last<any>;
+declare type T28 = Last<never>;
+declare type T30 = DropLast<[number, symbol, string]>;
+declare type T31 = DropLast<[symbol, string]>;
+declare type T32 = DropLast<[string]>;
+declare type T33 = DropLast<[number, symbol, ...string[]]>;
+declare type T34 = DropLast<[symbol, ...string[]]>;
+declare type T35 = DropLast<string[]>;
+declare type T36 = DropLast<[]>;
+declare type T37 = DropLast<any>;
+declare type T38 = DropLast<never>;
+declare type R00 = First<readonly [number, symbol, string]>;
+declare type R01 = First<readonly [symbol, string]>;
+declare type R02 = First<readonly [string]>;
+declare type R03 = First<readonly [number, symbol, ...string[]]>;
+declare type R04 = First<readonly [symbol, ...string[]]>;
+declare type R05 = First<readonly string[]>;
+declare type R06 = First<readonly []>;
+declare type R10 = DropFirst<readonly [number, symbol, string]>;
+declare type R11 = DropFirst<readonly [symbol, string]>;
+declare type R12 = DropFirst<readonly [string]>;
+declare type R13 = DropFirst<readonly [number, symbol, ...string[]]>;
+declare type R14 = DropFirst<readonly [symbol, ...string[]]>;
+declare type R15 = DropFirst<readonly string[]>;
+declare type R16 = DropFirst<readonly []>;
+declare type R20 = Last<readonly [number, symbol, string]>;
+declare type R21 = Last<readonly [symbol, string]>;
+declare type R22 = Last<readonly [string]>;
+declare type R23 = Last<readonly [number, symbol, ...string[]]>;
+declare type R24 = Last<readonly [symbol, ...string[]]>;
+declare type R25 = Last<readonly string[]>;
+declare type R26 = Last<readonly []>;
+declare type R30 = DropLast<readonly [number, symbol, string]>;
+declare type R31 = DropLast<readonly [symbol, string]>;
+declare type R32 = DropLast<readonly [string]>;
+declare type R33 = DropLast<readonly [number, symbol, ...string[]]>;
+declare type R34 = DropLast<readonly [symbol, ...string[]]>;
+declare type R35 = DropLast<readonly string[]>;
+declare type R36 = DropLast<readonly []>;
+declare function curry<T extends unknown[], U extends unknown[], R>(f: (...args: [...T, ...U]) => R, ...a: T): (...b: U) => R;
+declare const fn1: (a: number, b: string, c: boolean, d: string[]) => number;
+declare const c0: (a: number, b: string, c: boolean, d: string[]) => number;
+declare const c1: (b: string, c: boolean, d: string[]) => number;
+declare const c2: (c: boolean, d: string[]) => number;
+declare const c3: (d: string[]) => number;
+declare const c4: () => number;
+declare const fn2: (x: number, b: boolean, ...args: string[]) => number;
+declare const c10: (x: number, b: boolean, ...args: string[]) => number;
+declare const c11: (b: boolean, ...args: string[]) => number;
+declare const c12: (...b: string[]) => number;
+declare const c13: (...b: string[]) => number;
+declare const fn3: (...args: string[]) => number;
+declare const c20: (...b: string[]) => number;
+declare const c21: (...b: string[]) => number;
+declare const c22: (...b: string[]) => number;
+declare function curry2<T extends unknown[], U extends unknown[], R>(f: (...args: [...T, ...U]) => R, t: [...T], u: [...U]): R;
+declare function fn10(a: string, b: number, c: boolean): string[];
+declare function call<T extends unknown[], R>(...args: [...T, (...args: T) => R]): [T, R];

tests/baselines/reference/wideningTuples3.errors.txt

@@ -1,7 +1,6 @@
 tests/cases/conformance/types/tuple/wideningTuples3.ts(3,5): error TS7005: Variable 'b' implicitly has an '[any, any]' type.
 tests/cases/conformance/types/tuple/wideningTuples3.ts(3,9): error TS2322: Type '[undefined, null]' is not assignable to type '[any]'.
-  Types of property 'length' are incompatible.
-    Type '2' is not assignable to type '1'.
+  Source has 2 element(s) but target allows only 1.
 
 
 ==== tests/cases/conformance/types/tuple/wideningTuples3.ts (2 errors) ====
@@ -12,5 +11,4 @@ tests/cases/conformance/types/tuple/wideningTuples3.ts(3,9): error TS2322: Type
 !!! error TS7005: Variable 'b' implicitly has an '[any, any]' type.
             ~
 !!! error TS2322: Type '[undefined, null]' is not assignable to type '[any]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '2' is not assignable to type '1'.
+!!! error TS2322:   Source has 2 element(s) but target allows only 1.

tests/baselines/reference/wideningTuples4.errors.txt

@@ -1,6 +1,5 @@
 tests/cases/conformance/types/tuple/wideningTuples4.ts(3,9): error TS2322: Type '[undefined, null]' is not assignable to type '[any]'.
-  Types of property 'length' are incompatible.
-    Type '2' is not assignable to type '1'.
+  Source has 2 element(s) but target allows only 1.
 
 
 ==== tests/cases/conformance/types/tuple/wideningTuples4.ts (1 errors) ====
@@ -9,6 +8,5 @@ tests/cases/conformance/types/tuple/wideningTuples4.ts(3,9): error TS2322: Type
     var b = a = [undefined, null];
             ~
 !!! error TS2322: Type '[undefined, null]' is not assignable to type '[any]'.
-!!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type '2' is not assignable to type '1'.
+!!! error TS2322:   Source has 2 element(s) but target allows only 1.
     b = ["", ""];

tests/cases/conformance/types/tuple/variadicTuples1.ts

@@ -0,0 +1,300 @@
+// @strict: true
+// @declaration: true
+
+// Variadics in tuple types
+
+type TV0<T extends unknown[]> = [string, ...T];
+type TV1<T extends unknown[]> = [string, ...T, number];
+type TV2<T extends unknown[]> = [string, ...T, number, ...T];
+type TV3<T extends unknown[]> = [string, ...T, ...number[], ...T];  // Error
+
+// Normalization
+
+type TN1 = TV1<[boolean, string]>;
+type TN2 = TV1<[]>;
+type TN3 = TV1<[boolean?]>;
+type TN4 = TV1<string[]>;
+type TN5 = TV1<[boolean] | [symbol, symbol]>;
+type TN6 = TV1<any>;
+type TN7 = TV1<never>;
+
+// Variadics in array literals
+
+function tup2<T extends unknown[], U extends unknown[]>(t: [...T], u: [...U]) {
+    return [1, ...t, 2, ...u, 3] as const;
+}
+
+const t2 = tup2(['hello'], [10, true]);
+
+function concat<T extends unknown[], U extends unknown[]>(t: [...T], u: [...U]): [...T, ...U] {
+    return [...t, ...u];
+}
+
+declare const sa: string[];
+
+const tc1 = concat([], []);
+const tc2 = concat(['hello'], [42]);
+const tc3 = concat([1, 2, 3], sa);
+const tc4 = concat(sa, [1, 2, 3]);  // Ideally would be [...string[], number, number, number]
+
+// Spread arguments
+
+declare function foo1(a: number, b: string, c: boolean, ...d: number[]): void;
+
+function foo2(t1: [number, string], t2: [boolean], a1: number[]) {
+    foo1(1, 'abc', true, 42, 43, 44);
+    foo1(...t1, true, 42, 43, 44);
+    foo1(...t1, ...t2, 42, 43, 44);
+    foo1(...t1, ...t2, ...a1);
+    foo1(...t1);  // Error
+    foo1(...t1, 45);  // Error
+}
+
+declare function foo3<T extends unknown[]>(x: number, ...args: [...T, number]): T;
+
+function foo4<U extends unknown[]>(u: U) {
+    foo3(1, 2);
+    foo3(1, 'hello', true, 2);
+    foo3(1, ...u, 'hi', 2);
+    foo3(1);
+}
+
+// Contextual typing of array literals
+
+declare function ft1<T extends unknown[]>(t: T): T;
+declare function ft2<T extends unknown[]>(t: T): readonly [...T];
+declare function ft3<T extends unknown[]>(t: [...T]): T;
+declare function ft4<T extends unknown[]>(t: [...T]): readonly [...T];
+
+ft1(['hello', 42]);  // (string | number)[]
+ft2(['hello', 42]);  // readonly (string | number)[]
+ft3(['hello', 42]);  // [string, number]
+ft4(['hello', 42]);  // readonly [string, number]
+
+// Indexing variadic tuple types
+
+function f0<T extends unknown[]>(t: [string, ...T], n: number) {
+    const a = t[0];  // string
+    const b = t[1];  // [string, ...T][1]
+    const c = t[2];  // [string, ...T][2]
+    const d = t[n];  // [string, ...T][number]
+}
+
+function f1<T extends unknown[]>(t: [string, ...T, number], n: number) {
+    const a = t[0];  // string
+    const b = t[1];  // [string, ...T, number][1]
+    const c = t[2];  // [string, ...T, number][2]
+    const d = t[n];  // [string, ...T, number][number]
+}
+
+// Destructuring variadic tuple types
+
+function f2<T extends unknown[]>(t: [string, ...T]) {
+    let [...ax] = t;  // [string, ...T]
+    let [b1, ...bx] = t;  // string, [...T]
+    let [c1, c2, ...cx] = t;  // string, [string, ...T][1], T[number][]
+}
+
+function f3<T extends unknown[]>(t: [string, ...T, number]) {
+    let [...ax] = t;  // [string, ...T, number]
+    let [b1, ...bx] = t;  // string, [...T, number]
+    let [c1, c2, ...cx] = t;  // string, [string, ...T, number][1], (number | T[number])[]
+}
+
+// Mapped types applied to variadic tuple types
+
+type Arrayify<T> = { [P in keyof T]: T[P][] };
+
+type TM1<U extends unknown[]> = Arrayify<readonly [string, number?, ...U, ...boolean[]]>;  // [string[], (number | undefined)[]?, Arrayify<U>, ...boolean[][]]
+
+type TP1<T extends unknown[]> = Partial<[string, ...T, number]>;  // [string?, Partial<T>, number?]
+type TP2<T extends unknown[]> = Partial<[string, ...T, ...number[]]>;  // [string?, Partial<T>, ...(number | undefined)[]]
+
+// Reverse mapping through mapped type applied to variadic tuple type
+
+declare function fm1<T extends unknown[]>(t: Arrayify<[string, number, ...T]>): T;
+
+let tm1 = fm1([['abc'], [42], [true], ['def']]);  // [boolean, string]
+
+// Spread of readonly array-like infers mutable array-like
+
+declare function fx1<T extends unknown[]>(a: string, ...args: T): T;
+
+function gx1<U extends unknown[], V extends readonly unknown[]>(u: U, v: V) {
+    fx1('abc');  // []
+    fx1('abc', ...u);  // U
+    fx1('abc', ...v);  // [...V]
+    fx1<U>('abc', ...u);  // U
+    fx1<V>('abc', ...v);  // Error
+}
+
+declare function fx2<T extends readonly unknown[]>(a: string, ...args: T): T;
+
+function gx2<U extends unknown[], V extends readonly unknown[]>(u: U, v: V) {
+    fx2('abc');  // []
+    fx2('abc', ...u);  // U
+    fx2('abc', ...v);  // [...V]
+    fx2<U>('abc', ...u);  // U
+    fx2<V>('abc', ...v);  // V
+}
+
+// Relations involving variadic tuple types
+
+function f10<T extends string[], U extends T>(x: [string, ...unknown[]], y: [string, ...T], z: [string, ...U]) {
+    x = y;
+    x = z;
+    y = x;  // Error
+    y = z;
+    z = x;  // Error
+    z = y;  // Error
+}
+
+// For a generic type T, [...T] is assignable to T, T is assignable to readonly [...T], and T is assignable
+// to [...T] when T is constrained to a mutable array or tuple type.
+
+function f11<T extends unknown[]>(t: T, m: [...T], r: readonly [...T]) {
+    t = m;
+    t = r;  // Error
+    m = t;
+    m = r;  // Error
+    r = t;
+    r = m;
+}
+
+function f12<T extends readonly unknown[]>(t: T, m: [...T], r: readonly [...T]) {
+    t = m;
+    t = r;  // Error
+    m = t;  // Error
+    m = r;  // Error
+    r = t;
+    r = m;
+}
+
+// Inference between variadic tuple types
+
+type First<T extends readonly unknown[]> = T[0];
+type DropFirst<T extends readonly unknown[]> = T extends readonly [any, ...infer U] ? U : [...T];
+
+type Last<T extends readonly unknown[]> = T extends readonly [...infer _, infer U] ? U : undefined;
+type DropLast<T extends readonly unknown[]> = T extends readonly [...infer U, any] ? U : [...T];
+
+type T00 = First<[number, symbol, string]>;
+type T01 = First<[symbol, string]>;
+type T02 = First<[string]>;
+type T03 = First<[number, symbol, ...string[]]>;
+type T04 = First<[symbol, ...string[]]>;
+type T05 = First<string[]>;
+type T06 = First<[]>;
+type T07 = First<any>;
+type T08 = First<never>;
+
+type T10 = DropFirst<[number, symbol, string]>;
+type T11 = DropFirst<[symbol, string]>;
+type T12 = DropFirst<[string]>;
+type T13 = DropFirst<[number, symbol, ...string[]]>;
+type T14 = DropFirst<[symbol, ...string[]]>;
+type T15 = DropFirst<string[]>;
+type T16 = DropFirst<[]>;
+type T17 = DropFirst<any>;
+type T18 = DropFirst<never>;
+
+type T20 = Last<[number, symbol, string]>;
+type T21 = Last<[symbol, string]>;
+type T22 = Last<[string]>;
+type T23 = Last<[number, symbol, ...string[]]>;
+type T24 = Last<[symbol, ...string[]]>;
+type T25 = Last<string[]>;
+type T26 = Last<[]>;  // unknown[], maybe should be []
+type T27 = Last<any>;  // unknown, maybe should be any
+type T28 = Last<never>;
+
+type T30 = DropLast<[number, symbol, string]>;
+type T31 = DropLast<[symbol, string]>;
+type T32 = DropLast<[string]>;
+type T33 = DropLast<[number, symbol, ...string[]]>;
+type T34 = DropLast<[symbol, ...string[]]>;
+type T35 = DropLast<string[]>;
+type T36 = DropLast<[]>;  // unknown[], maybe should be []
+type T37 = DropLast<any>;
+type T38 = DropLast<never>;
+
+type R00 = First<readonly [number, symbol, string]>;
+type R01 = First<readonly [symbol, string]>;
+type R02 = First<readonly [string]>;
+type R03 = First<readonly [number, symbol, ...string[]]>;
+type R04 = First<readonly [symbol, ...string[]]>;
+type R05 = First<readonly string[]>;
+type R06 = First<readonly []>;
+
+type R10 = DropFirst<readonly [number, symbol, string]>;
+type R11 = DropFirst<readonly [symbol, string]>;
+type R12 = DropFirst<readonly [string]>;
+type R13 = DropFirst<readonly [number, symbol, ...string[]]>;
+type R14 = DropFirst<readonly [symbol, ...string[]]>;
+type R15 = DropFirst<readonly string[]>;
+type R16 = DropFirst<readonly []>;
+
+type R20 = Last<readonly [number, symbol, string]>;
+type R21 = Last<readonly [symbol, string]>;
+type R22 = Last<readonly [string]>;
+type R23 = Last<readonly [number, symbol, ...string[]]>;
+type R24 = Last<readonly [symbol, ...string[]]>;
+type R25 = Last<readonly string[]>;
+type R26 = Last<readonly []>;
+
+type R30 = DropLast<readonly [number, symbol, string]>;
+type R31 = DropLast<readonly [symbol, string]>;
+type R32 = DropLast<readonly [string]>;
+type R33 = DropLast<readonly [number, symbol, ...string[]]>;
+type R34 = DropLast<readonly [symbol, ...string[]]>;
+type R35 = DropLast<readonly string[]>;
+type R36 = DropLast<readonly []>;
+
+// Inference to [...T, ...U] with implied arity for T
+
+function curry<T extends unknown[], U extends unknown[], R>(f: (...args: [...T, ...U]) => R, ...a: T) {
+    return (...b: U) => f(...a, ...b);
+}
+
+const fn1 = (a: number, b: string, c: boolean, d: string[]) => 0;
+
+const c0 = curry(fn1);  // (a: number, b: string, c: boolean, d: string[]) => number
+const c1 = curry(fn1, 1);  // (b: string, c: boolean, d: string[]) => number
+const c2 = curry(fn1, 1, 'abc');  // (c: boolean, d: string[]) => number
+const c3 = curry(fn1, 1, 'abc', true);  // (d: string[]) => number
+const c4 = curry(fn1, 1, 'abc', true, ['x', 'y']);  // () => number
+
+const fn2 = (x: number, b: boolean, ...args: string[]) => 0;
+
+const c10 = curry(fn2);  // (x: number, b: boolean, ...args: string[]) => number
+const c11 = curry(fn2, 1);  // (b: boolean, ...args: string[]) => number
+const c12 = curry(fn2, 1, true);  // (...args: string[]) => number
+const c13 = curry(fn2, 1, true, 'abc', 'def');  // (...args: string[]) => number
+
+const fn3 = (...args: string[]) => 0;
+
+const c20 = curry(fn3);  // (...args: string[]) => number
+const c21 = curry(fn3, 'abc', 'def');  // (...args: string[]) => number
+const c22 = curry(fn3, ...sa);  // (...args: string[]) => number
+
+// No inference to [...T, ...U] when there is no implied arity
+
+function curry2<T extends unknown[], U extends unknown[], R>(f: (...args: [...T, ...U]) => R, t: [...T], u: [...U]) {
+    return f(...t, ...u);
+}
+
+declare function fn10(a: string, b: number, c: boolean): string[];
+
+curry2(fn10, ['hello', 42], [true]);
+curry2(fn10, ['hello'], [42, true]);
+
+// Last argument is contextually typed
+
+declare function call<T extends unknown[], R>(...args: [...T, (...args: T) => R]): [T, R];
+
+call('hello', 32, (a, b) => 42);
+
+// Would be nice to infer [...string[], (...args: string[]) => number] here
+// Requires [starting-fixed-part, ...rest-part, ending-fixed-part] tuple structure
+
+call(...sa, (...x) => 42);