When calculating spreads, merge empty object into nonempty object to … (#34853)

* When calculating spreads, merge empty object into nonempty object to produce partial object to reduce complexity

* Actually accept remainder of baselines

* Limit simplification to single prop or partial types

src/compiler/checker.ts

@@ -12524,6 +12524,61 @@ namespace ts {
             return !!(type.flags & TypeFlags.Object) && !isGenericMappedType(type);
         }
 
+        function isEmptyObjectTypeOrSpreadsIntoEmptyObject(type: Type) {
+            return isEmptyObjectType(type) || !!(type.flags & (TypeFlags.Null | TypeFlags.Undefined | TypeFlags.BooleanLike | TypeFlags.NumberLike | TypeFlags.BigIntLike | TypeFlags.StringLike | TypeFlags.EnumLike | TypeFlags.NonPrimitive | TypeFlags.Index));
+        }
+
+        function isSinglePropertyAnonymousObjectType(type: Type) {
+            return !!(type.flags & TypeFlags.Object) &&
+                !!(getObjectFlags(type) & ObjectFlags.Anonymous) &&
+                (length(getPropertiesOfType(type)) === 1 || every(getPropertiesOfType(type), p => !!(p.flags & SymbolFlags.Optional)));
+        }
+
+        function tryMergeUnionOfObjectTypeAndEmptyObject(type: UnionType, readonly: boolean): Type | undefined {
+            if (type.types.length === 2) {
+                const firstType = type.types[0];
+                const secondType = type.types[1];
+                if (every(type.types, isEmptyObjectTypeOrSpreadsIntoEmptyObject)) {
+                    return isEmptyObjectType(firstType) ? firstType : isEmptyObjectType(secondType) ? secondType : emptyObjectType;
+                }
+                if (isEmptyObjectTypeOrSpreadsIntoEmptyObject(firstType) && isSinglePropertyAnonymousObjectType(secondType)) {
+                    return getAnonymousPartialType(secondType);
+                }
+                if (isEmptyObjectTypeOrSpreadsIntoEmptyObject(secondType) && isSinglePropertyAnonymousObjectType(firstType)) {
+                    return getAnonymousPartialType(firstType);
+                }
+            }
+
+            function getAnonymousPartialType(type: Type) {
+                // gets the type as if it had been spread, but where everything in the spread is made optional
+                const members = createSymbolTable();
+                for (const prop of getPropertiesOfType(type)) {
+                    if (getDeclarationModifierFlagsFromSymbol(prop) & (ModifierFlags.Private | ModifierFlags.Protected)) {
+                        // do nothing, skip privates
+                    }
+                    else if (isSpreadableProperty(prop)) {
+                        const isSetonlyAccessor = prop.flags & SymbolFlags.SetAccessor && !(prop.flags & SymbolFlags.GetAccessor);
+                        const flags = SymbolFlags.Property | SymbolFlags.Optional;
+                        const result = createSymbol(flags, prop.escapedName, readonly ? CheckFlags.Readonly : 0);
+                        result.type = isSetonlyAccessor ? undefinedType : getTypeOfSymbol(prop);
+                        result.declarations = prop.declarations;
+                        result.nameType = prop.nameType;
+                        result.syntheticOrigin = prop;
+                        members.set(prop.escapedName, result);
+                    }
+                }
+                const spread = createAnonymousType(
+                    type.symbol,
+                    members,
+                    emptyArray,
+                    emptyArray,
+                    getIndexInfoOfType(type, IndexKind.String),
+                    getIndexInfoOfType(type, IndexKind.Number));
+                spread.objectFlags |= ObjectFlags.ObjectLiteral | ObjectFlags.ContainsObjectOrArrayLiteral;
+                return spread;
+            }
+        }
+
         /**
          * Since the source of spread types are object literals, which are not binary,
          * this function should be called in a left folding style, with left = previous result of getSpreadType
@@ -12543,9 +12598,17 @@ namespace ts {
                 return left;
             }
             if (left.flags & TypeFlags.Union) {
+                const merged = tryMergeUnionOfObjectTypeAndEmptyObject(left as UnionType, readonly);
+                if (merged) {
+                    return getSpreadType(merged, right, symbol, objectFlags, readonly);
+                }
                 return mapType(left, t => getSpreadType(t, right, symbol, objectFlags, readonly));
             }
             if (right.flags & TypeFlags.Union) {
+                const merged = tryMergeUnionOfObjectTypeAndEmptyObject(right as UnionType, readonly);
+                if (merged) {
+                    return getSpreadType(left, merged, symbol, objectFlags, readonly);
+                }
                 return mapType(right, t => getSpreadType(left, t, symbol, objectFlags, readonly));
             }
             if (right.flags & (TypeFlags.BooleanLike | TypeFlags.NumberLike | TypeFlags.BigIntLike | TypeFlags.StringLike | TypeFlags.EnumLike | TypeFlags.NonPrimitive | TypeFlags.Index)) {

tests/baselines/reference/objectSpread.types

@@ -244,7 +244,7 @@ function from16326(this: { header: Header }, header: Header, authToken: string):
 >authToken : string
 
     return {
->{        ...this.header,        ...header,        ...authToken && { authToken }    } : { head: string; body: string; authToken: string; } | { authToken: string; head: string; body: string; }
+>{        ...this.header,        ...header,        ...authToken && { authToken }    } : { authToken: string; head: string; body: string; }
 
         ...this.header,
 >this.header : Header
@@ -277,9 +277,9 @@ function conditionalSpreadBoolean(b: boolean) : { x: number, y: number } {
 >13 : 13
 
     o = {
->o = {        ...o,        ...b && { x: 14 }    } : { x: number; y: number; } | { x: number; y: number; }
+>o = {        ...o,        ...b && { x: 14 }    } : { x: number; y: number; }
 >o : { x: number; y: number; }
->{        ...o,        ...b && { x: 14 }    } : { x: number; y: number; } | { x: number; y: number; }
+>{        ...o,        ...b && { x: 14 }    } : { x: number; y: number; }
 
         ...o,
 >o : { x: number; y: number; }
@@ -292,8 +292,8 @@ function conditionalSpreadBoolean(b: boolean) : { x: number, y: number } {
 >14 : 14
     }
     let o2 = { ...b && { x: 21 }}
->o2 : {}
->{ ...b && { x: 21 }} : { x: number; } | {}
+>o2 : { x?: number; }
+>{ ...b && { x: 21 }} : { x?: number; }
 >b && { x: 21 } : false | { x: number; }
 >b : boolean
 >{ x: 21 } : { x: number; }
@@ -318,9 +318,9 @@ function conditionalSpreadNumber(nt: number): { x: number, y: number } {
 >16 : 16
 
     o = {
->o = {        ...o,        ...nt && { x: nt }    } : { x: number; y: number; } | { x: number; y: number; }
+>o = {        ...o,        ...nt && { x: nt }    } : { x: number; y: number; }
 >o : { x: number; y: number; }
->{        ...o,        ...nt && { x: nt }    } : { x: number; y: number; } | { x: number; y: number; }
+>{        ...o,        ...nt && { x: nt }    } : { x: number; y: number; }
 
         ...o,
 >o : { x: number; y: number; }
@@ -333,8 +333,8 @@ function conditionalSpreadNumber(nt: number): { x: number, y: number } {
 >nt : number
     }
     let o2 = { ...nt && { x: nt }}
->o2 : {}
->{ ...nt && { x: nt }} : { x: number; } | {}
+>o2 : { x?: number; }
+>{ ...nt && { x: nt }} : { x?: number; }
 >nt && { x: nt } : 0 | { x: number; }
 >nt : number
 >{ x: nt } : { x: number; }
@@ -359,9 +359,9 @@ function conditionalSpreadString(st: string): { x: string, y: number } {
 >17 : 17
 
     o = {
->o = {        ...o,        ...st && { x: st }    } : { x: string; y: number; } | { x: string; y: number; }
+>o = {        ...o,        ...st && { x: st }    } : { x: string; y: number; }
 >o : { x: string; y: number; }
->{        ...o,        ...st && { x: st }    } : { x: string; y: number; } | { x: string; y: number; }
+>{        ...o,        ...st && { x: st }    } : { x: string; y: number; }
 
         ...o,
 >o : { x: string; y: number; }
@@ -374,8 +374,8 @@ function conditionalSpreadString(st: string): { x: string, y: number } {
 >st : string
     }
     let o2 = { ...st && { x: st }}
->o2 : {}
->{ ...st && { x: st }} : { x: string; } | {}
+>o2 : { x?: string; }
+>{ ...st && { x: st }} : { x?: string; }
 >st && { x: st } : "" | { x: string; }
 >st : string
 >{ x: st } : { x: string; }

tests/baselines/reference/objectSpreadIndexSignature.types

@@ -42,9 +42,9 @@ declare const b: boolean;
 >b : boolean
 
 indexed3 = { ...b ? indexed3 : undefined };
->indexed3 = { ...b ? indexed3 : undefined } : {} | { [n: string]: number; }
+>indexed3 = { ...b ? indexed3 : undefined } : { [n: string]: number; }
 >indexed3 : { [n: string]: number; }
->{ ...b ? indexed3 : undefined } : {} | { [n: string]: number; }
+>{ ...b ? indexed3 : undefined } : { [n: string]: number; }
 >b ? indexed3 : undefined : { [n: string]: number; } | undefined
 >b : boolean
 >indexed3 : { [n: string]: number; }

tests/baselines/reference/objectSpreadRepeatedNullCheckPerf.js

@@ -0,0 +1,80 @@
+//// [objectSpreadRepeatedNullCheckPerf.ts]
+interface Props {
+    readonly a?: string
+    readonly b?: string
+    readonly c?: string
+    readonly d?: string
+    readonly e?: string
+    readonly f?: string
+    readonly g?: string
+    readonly h?: string
+    readonly i?: string
+    readonly j?: string
+    readonly k?: string
+    readonly l?: string
+    readonly m?: string
+    readonly n?: string
+    readonly o?: string
+    readonly p?: string
+    readonly q?: string
+    readonly r?: string
+    readonly s?: string
+    readonly t?: string
+    readonly u?: string
+    readonly v?: string
+    readonly w?: string
+    readonly x?: string
+    readonly y?: string
+    readonly z?: string
+}
+
+function parseWithSpread(config: Record<string, number>): Props {
+    return {
+        ...config.a !== undefined && { a: config.a.toString() },
+        ...config.b !== undefined && { b: config.b.toString() },
+        ...config.c !== undefined && { c: config.c.toString() },
+        ...config.d !== undefined && { d: config.d.toString() },
+        ...config.e !== undefined && { e: config.e.toString() },
+        ...config.f !== undefined && { f: config.f.toString() },
+        ...config.g !== undefined && { g: config.g.toString() },
+        ...config.h !== undefined && { h: config.h.toString() },
+        ...config.i !== undefined && { i: config.i.toString() },
+        ...config.j !== undefined && { j: config.j.toString() },
+        ...config.k !== undefined && { k: config.k.toString() },
+        ...config.l !== undefined && { l: config.l.toString() },
+        ...config.m !== undefined && { m: config.m.toString() },
+        ...config.n !== undefined && { n: config.n.toString() },
+        ...config.o !== undefined && { o: config.o.toString() },
+        ...config.p !== undefined && { p: config.p.toString() },
+        ...config.q !== undefined && { q: config.q.toString() },
+        ...config.r !== undefined && { r: config.r.toString() },
+        ...config.s !== undefined && { s: config.s.toString() },
+        ...config.t !== undefined && { t: config.t.toString() },
+        ...config.u !== undefined && { u: config.u.toString() },
+        ...config.v !== undefined && { v: config.v.toString() },
+        ...config.w !== undefined && { w: config.w.toString() },
+        ...config.x !== undefined && { x: config.x.toString() },
+        ...config.y !== undefined && { y: config.y.toString() },
+        ...config.z !== undefined && { z: config.z.toString() }
+    }
+}
+
+parseWithSpread({ a: 1, b: 2, z: 26 })
+
+//// [objectSpreadRepeatedNullCheckPerf.js]
+"use strict";
+var __assign = (this && this.__assign) || function () {
+    __assign = Object.assign || function(t) {
+        for (var s, i = 1, n = arguments.length; i < n; i++) {
+            s = arguments[i];
+            for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p))
+                t[p] = s[p];
+        }
+        return t;
+    };
+    return __assign.apply(this, arguments);
+};
+function parseWithSpread(config) {
+    return __assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign(__assign({}, config.a !== undefined && { a: config.a.toString() }), config.b !== undefined && { b: config.b.toString() }), config.c !== undefined && { c: config.c.toString() }), config.d !== undefined && { d: config.d.toString() }), config.e !== undefined && { e: config.e.toString() }), config.f !== undefined && { f: config.f.toString() }), config.g !== undefined && { g: config.g.toString() }), config.h !== undefined && { h: config.h.toString() }), config.i !== undefined && { i: config.i.toString() }), config.j !== undefined && { j: config.j.toString() }), config.k !== undefined && { k: config.k.toString() }), config.l !== undefined && { l: config.l.toString() }), config.m !== undefined && { m: config.m.toString() }), config.n !== undefined && { n: config.n.toString() }), config.o !== undefined && { o: config.o.toString() }), config.p !== undefined && { p: config.p.toString() }), config.q !== undefined && { q: config.q.toString() }), config.r !== undefined && { r: config.r.toString() }), config.s !== undefined && { s: config.s.toString() }), config.t !== undefined && { t: config.t.toString() }), config.u !== undefined && { u: config.u.toString() }), config.v !== undefined && { v: config.v.toString() }), config.w !== undefined && { w: config.w.toString() }), config.x !== undefined && { x: config.x.toString() }), config.y !== undefined && { y: config.y.toString() }), config.z !== undefined && { z: config.z.toString() });
+}
+parseWithSpread({ a: 1, b: 2, z: 26 });

tests/baselines/reference/objectSpreadRepeatedNullCheckPerf.symbols

@@ -0,0 +1,306 @@
+=== tests/cases/conformance/types/spread/objectSpreadRepeatedNullCheckPerf.ts ===
+interface Props {
+>Props : Symbol(Props, Decl(objectSpreadRepeatedNullCheckPerf.ts, 0, 0))
+
+    readonly a?: string
+>a : Symbol(Props.a, Decl(objectSpreadRepeatedNullCheckPerf.ts, 0, 17))
+
+    readonly b?: string
+>b : Symbol(Props.b, Decl(objectSpreadRepeatedNullCheckPerf.ts, 1, 23))
+
+    readonly c?: string
+>c : Symbol(Props.c, Decl(objectSpreadRepeatedNullCheckPerf.ts, 2, 23))
+
+    readonly d?: string
+>d : Symbol(Props.d, Decl(objectSpreadRepeatedNullCheckPerf.ts, 3, 23))
+
+    readonly e?: string
+>e : Symbol(Props.e, Decl(objectSpreadRepeatedNullCheckPerf.ts, 4, 23))
+
+    readonly f?: string
+>f : Symbol(Props.f, Decl(objectSpreadRepeatedNullCheckPerf.ts, 5, 23))
+
+    readonly g?: string
+>g : Symbol(Props.g, Decl(objectSpreadRepeatedNullCheckPerf.ts, 6, 23))
+
+    readonly h?: string
+>h : Symbol(Props.h, Decl(objectSpreadRepeatedNullCheckPerf.ts, 7, 23))
+
+    readonly i?: string
+>i : Symbol(Props.i, Decl(objectSpreadRepeatedNullCheckPerf.ts, 8, 23))
+
+    readonly j?: string
+>j : Symbol(Props.j, Decl(objectSpreadRepeatedNullCheckPerf.ts, 9, 23))
+
+    readonly k?: string
+>k : Symbol(Props.k, Decl(objectSpreadRepeatedNullCheckPerf.ts, 10, 23))
+
+    readonly l?: string
+>l : Symbol(Props.l, Decl(objectSpreadRepeatedNullCheckPerf.ts, 11, 23))
+
+    readonly m?: string
+>m : Symbol(Props.m, Decl(objectSpreadRepeatedNullCheckPerf.ts, 12, 23))
+
+    readonly n?: string
+>n : Symbol(Props.n, Decl(objectSpreadRepeatedNullCheckPerf.ts, 13, 23))
+
+    readonly o?: string
+>o : Symbol(Props.o, Decl(objectSpreadRepeatedNullCheckPerf.ts, 14, 23))
+
+    readonly p?: string
+>p : Symbol(Props.p, Decl(objectSpreadRepeatedNullCheckPerf.ts, 15, 23))
+
+    readonly q?: string
+>q : Symbol(Props.q, Decl(objectSpreadRepeatedNullCheckPerf.ts, 16, 23))
+
+    readonly r?: string
+>r : Symbol(Props.r, Decl(objectSpreadRepeatedNullCheckPerf.ts, 17, 23))
+
+    readonly s?: string
+>s : Symbol(Props.s, Decl(objectSpreadRepeatedNullCheckPerf.ts, 18, 23))
+
+    readonly t?: string
+>t : Symbol(Props.t, Decl(objectSpreadRepeatedNullCheckPerf.ts, 19, 23))
+
+    readonly u?: string
+>u : Symbol(Props.u, Decl(objectSpreadRepeatedNullCheckPerf.ts, 20, 23))
+
+    readonly v?: string
+>v : Symbol(Props.v, Decl(objectSpreadRepeatedNullCheckPerf.ts, 21, 23))
+
+    readonly w?: string
+>w : Symbol(Props.w, Decl(objectSpreadRepeatedNullCheckPerf.ts, 22, 23))
+
+    readonly x?: string
+>x : Symbol(Props.x, Decl(objectSpreadRepeatedNullCheckPerf.ts, 23, 23))
+
+    readonly y?: string
+>y : Symbol(Props.y, Decl(objectSpreadRepeatedNullCheckPerf.ts, 24, 23))
+
+    readonly z?: string
+>z : Symbol(Props.z, Decl(objectSpreadRepeatedNullCheckPerf.ts, 25, 23))
+}
+
+function parseWithSpread(config: Record<string, number>): Props {
+>parseWithSpread : Symbol(parseWithSpread, Decl(objectSpreadRepeatedNullCheckPerf.ts, 27, 1))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>Props : Symbol(Props, Decl(objectSpreadRepeatedNullCheckPerf.ts, 0, 0))
+
+    return {
+        ...config.a !== undefined && { a: config.a.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>a : Symbol(a, Decl(objectSpreadRepeatedNullCheckPerf.ts, 31, 38))
+>config.a.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.b !== undefined && { b: config.b.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>b : Symbol(b, Decl(objectSpreadRepeatedNullCheckPerf.ts, 32, 38))
+>config.b.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.c !== undefined && { c: config.c.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>c : Symbol(c, Decl(objectSpreadRepeatedNullCheckPerf.ts, 33, 38))
+>config.c.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.d !== undefined && { d: config.d.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>d : Symbol(d, Decl(objectSpreadRepeatedNullCheckPerf.ts, 34, 38))
+>config.d.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.e !== undefined && { e: config.e.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>e : Symbol(e, Decl(objectSpreadRepeatedNullCheckPerf.ts, 35, 38))
+>config.e.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.f !== undefined && { f: config.f.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>f : Symbol(f, Decl(objectSpreadRepeatedNullCheckPerf.ts, 36, 38))
+>config.f.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.g !== undefined && { g: config.g.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>g : Symbol(g, Decl(objectSpreadRepeatedNullCheckPerf.ts, 37, 38))
+>config.g.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.h !== undefined && { h: config.h.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>h : Symbol(h, Decl(objectSpreadRepeatedNullCheckPerf.ts, 38, 38))
+>config.h.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.i !== undefined && { i: config.i.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>i : Symbol(i, Decl(objectSpreadRepeatedNullCheckPerf.ts, 39, 38))
+>config.i.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.j !== undefined && { j: config.j.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>j : Symbol(j, Decl(objectSpreadRepeatedNullCheckPerf.ts, 40, 38))
+>config.j.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.k !== undefined && { k: config.k.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>k : Symbol(k, Decl(objectSpreadRepeatedNullCheckPerf.ts, 41, 38))
+>config.k.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.l !== undefined && { l: config.l.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>l : Symbol(l, Decl(objectSpreadRepeatedNullCheckPerf.ts, 42, 38))
+>config.l.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.m !== undefined && { m: config.m.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>m : Symbol(m, Decl(objectSpreadRepeatedNullCheckPerf.ts, 43, 38))
+>config.m.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.n !== undefined && { n: config.n.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>n : Symbol(n, Decl(objectSpreadRepeatedNullCheckPerf.ts, 44, 38))
+>config.n.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.o !== undefined && { o: config.o.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>o : Symbol(o, Decl(objectSpreadRepeatedNullCheckPerf.ts, 45, 38))
+>config.o.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.p !== undefined && { p: config.p.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>p : Symbol(p, Decl(objectSpreadRepeatedNullCheckPerf.ts, 46, 38))
+>config.p.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.q !== undefined && { q: config.q.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>q : Symbol(q, Decl(objectSpreadRepeatedNullCheckPerf.ts, 47, 38))
+>config.q.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.r !== undefined && { r: config.r.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>r : Symbol(r, Decl(objectSpreadRepeatedNullCheckPerf.ts, 48, 38))
+>config.r.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.s !== undefined && { s: config.s.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>s : Symbol(s, Decl(objectSpreadRepeatedNullCheckPerf.ts, 49, 38))
+>config.s.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.t !== undefined && { t: config.t.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>t : Symbol(t, Decl(objectSpreadRepeatedNullCheckPerf.ts, 50, 38))
+>config.t.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.u !== undefined && { u: config.u.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>u : Symbol(u, Decl(objectSpreadRepeatedNullCheckPerf.ts, 51, 38))
+>config.u.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.v !== undefined && { v: config.v.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>v : Symbol(v, Decl(objectSpreadRepeatedNullCheckPerf.ts, 52, 38))
+>config.v.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.w !== undefined && { w: config.w.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>w : Symbol(w, Decl(objectSpreadRepeatedNullCheckPerf.ts, 53, 38))
+>config.w.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.x !== undefined && { x: config.x.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>x : Symbol(x, Decl(objectSpreadRepeatedNullCheckPerf.ts, 54, 38))
+>config.x.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.y !== undefined && { y: config.y.toString() },
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>y : Symbol(y, Decl(objectSpreadRepeatedNullCheckPerf.ts, 55, 38))
+>config.y.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+
+        ...config.z !== undefined && { z: config.z.toString() }
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>undefined : Symbol(undefined)
+>z : Symbol(z, Decl(objectSpreadRepeatedNullCheckPerf.ts, 56, 38))
+>config.z.toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+>config : Symbol(config, Decl(objectSpreadRepeatedNullCheckPerf.ts, 29, 25))
+>toString : Symbol(Number.toString, Decl(lib.es5.d.ts, --, --))
+    }
+}
+
+parseWithSpread({ a: 1, b: 2, z: 26 })
+>parseWithSpread : Symbol(parseWithSpread, Decl(objectSpreadRepeatedNullCheckPerf.ts, 27, 1))
+>a : Symbol(a, Decl(objectSpreadRepeatedNullCheckPerf.ts, 60, 17))
+>b : Symbol(b, Decl(objectSpreadRepeatedNullCheckPerf.ts, 60, 23))
+>z : Symbol(z, Decl(objectSpreadRepeatedNullCheckPerf.ts, 60, 29))
+

tests/baselines/reference/objectSpreadRepeatedNullCheckPerf.types

@@ -0,0 +1,517 @@
+=== tests/cases/conformance/types/spread/objectSpreadRepeatedNullCheckPerf.ts ===
+interface Props {
+    readonly a?: string
+>a : string | undefined
+
+    readonly b?: string
+>b : string | undefined
+
+    readonly c?: string
+>c : string | undefined
+
+    readonly d?: string
+>d : string | undefined
+
+    readonly e?: string
+>e : string | undefined
+
+    readonly f?: string
+>f : string | undefined
+
+    readonly g?: string
+>g : string | undefined
+
+    readonly h?: string
+>h : string | undefined
+
+    readonly i?: string
+>i : string | undefined
+
+    readonly j?: string
+>j : string | undefined
+
+    readonly k?: string
+>k : string | undefined
+
+    readonly l?: string
+>l : string | undefined
+
+    readonly m?: string
+>m : string | undefined
+
+    readonly n?: string
+>n : string | undefined
+
+    readonly o?: string
+>o : string | undefined
+
+    readonly p?: string
+>p : string | undefined
+
+    readonly q?: string
+>q : string | undefined
+
+    readonly r?: string
+>r : string | undefined
+
+    readonly s?: string
+>s : string | undefined
+
+    readonly t?: string
+>t : string | undefined
+
+    readonly u?: string
+>u : string | undefined
+
+    readonly v?: string
+>v : string | undefined
+
+    readonly w?: string
+>w : string | undefined
+
+    readonly x?: string
+>x : string | undefined
+
+    readonly y?: string
+>y : string | undefined
+
+    readonly z?: string
+>z : string | undefined
+}
+
+function parseWithSpread(config: Record<string, number>): Props {
+>parseWithSpread : (config: Record<string, number>) => Props
+>config : Record<string, number>
+
+    return {
+>{        ...config.a !== undefined && { a: config.a.toString() },        ...config.b !== undefined && { b: config.b.toString() },        ...config.c !== undefined && { c: config.c.toString() },        ...config.d !== undefined && { d: config.d.toString() },        ...config.e !== undefined && { e: config.e.toString() },        ...config.f !== undefined && { f: config.f.toString() },        ...config.g !== undefined && { g: config.g.toString() },        ...config.h !== undefined && { h: config.h.toString() },        ...config.i !== undefined && { i: config.i.toString() },        ...config.j !== undefined && { j: config.j.toString() },        ...config.k !== undefined && { k: config.k.toString() },        ...config.l !== undefined && { l: config.l.toString() },        ...config.m !== undefined && { m: config.m.toString() },        ...config.n !== undefined && { n: config.n.toString() },        ...config.o !== undefined && { o: config.o.toString() },        ...config.p !== undefined && { p: config.p.toString() },        ...config.q !== undefined && { q: config.q.toString() },        ...config.r !== undefined && { r: config.r.toString() },        ...config.s !== undefined && { s: config.s.toString() },        ...config.t !== undefined && { t: config.t.toString() },        ...config.u !== undefined && { u: config.u.toString() },        ...config.v !== undefined && { v: config.v.toString() },        ...config.w !== undefined && { w: config.w.toString() },        ...config.x !== undefined && { x: config.x.toString() },        ...config.y !== undefined && { y: config.y.toString() },        ...config.z !== undefined && { z: config.z.toString() }    } : { z?: string; y?: string; x?: string; w?: string; v?: string; u?: string; t?: string; s?: string; r?: string; q?: string; p?: string; o?: string; n?: string; m?: string; l?: string; k?: string; j?: string; i?: string; h?: string; g?: string; f?: string; e?: string; d?: string; c?: string; b?: string; a?: string; }
+
+        ...config.a !== undefined && { a: config.a.toString() },
+>config.a !== undefined && { a: config.a.toString() } : false | { a: string; }
+>config.a !== undefined : boolean
+>config.a : number
+>config : Record<string, number>
+>a : number
+>undefined : undefined
+>{ a: config.a.toString() } : { a: string; }
+>a : string
+>config.a.toString() : string
+>config.a.toString : (radix?: number | undefined) => string
+>config.a : number
+>config : Record<string, number>
+>a : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.b !== undefined && { b: config.b.toString() },
+>config.b !== undefined && { b: config.b.toString() } : false | { b: string; }
+>config.b !== undefined : boolean
+>config.b : number
+>config : Record<string, number>
+>b : number
+>undefined : undefined
+>{ b: config.b.toString() } : { b: string; }
+>b : string
+>config.b.toString() : string
+>config.b.toString : (radix?: number | undefined) => string
+>config.b : number
+>config : Record<string, number>
+>b : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.c !== undefined && { c: config.c.toString() },
+>config.c !== undefined && { c: config.c.toString() } : false | { c: string; }
+>config.c !== undefined : boolean
+>config.c : number
+>config : Record<string, number>
+>c : number
+>undefined : undefined
+>{ c: config.c.toString() } : { c: string; }
+>c : string
+>config.c.toString() : string
+>config.c.toString : (radix?: number | undefined) => string
+>config.c : number
+>config : Record<string, number>
+>c : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.d !== undefined && { d: config.d.toString() },
+>config.d !== undefined && { d: config.d.toString() } : false | { d: string; }
+>config.d !== undefined : boolean
+>config.d : number
+>config : Record<string, number>
+>d : number
+>undefined : undefined
+>{ d: config.d.toString() } : { d: string; }
+>d : string
+>config.d.toString() : string
+>config.d.toString : (radix?: number | undefined) => string
+>config.d : number
+>config : Record<string, number>
+>d : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.e !== undefined && { e: config.e.toString() },
+>config.e !== undefined && { e: config.e.toString() } : false | { e: string; }
+>config.e !== undefined : boolean
+>config.e : number
+>config : Record<string, number>
+>e : number
+>undefined : undefined
+>{ e: config.e.toString() } : { e: string; }
+>e : string
+>config.e.toString() : string
+>config.e.toString : (radix?: number | undefined) => string
+>config.e : number
+>config : Record<string, number>
+>e : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.f !== undefined && { f: config.f.toString() },
+>config.f !== undefined && { f: config.f.toString() } : false | { f: string; }
+>config.f !== undefined : boolean
+>config.f : number
+>config : Record<string, number>
+>f : number
+>undefined : undefined
+>{ f: config.f.toString() } : { f: string; }
+>f : string
+>config.f.toString() : string
+>config.f.toString : (radix?: number | undefined) => string
+>config.f : number
+>config : Record<string, number>
+>f : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.g !== undefined && { g: config.g.toString() },
+>config.g !== undefined && { g: config.g.toString() } : false | { g: string; }
+>config.g !== undefined : boolean
+>config.g : number
+>config : Record<string, number>
+>g : number
+>undefined : undefined
+>{ g: config.g.toString() } : { g: string; }
+>g : string
+>config.g.toString() : string
+>config.g.toString : (radix?: number | undefined) => string
+>config.g : number
+>config : Record<string, number>
+>g : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.h !== undefined && { h: config.h.toString() },
+>config.h !== undefined && { h: config.h.toString() } : false | { h: string; }
+>config.h !== undefined : boolean
+>config.h : number
+>config : Record<string, number>
+>h : number
+>undefined : undefined
+>{ h: config.h.toString() } : { h: string; }
+>h : string
+>config.h.toString() : string
+>config.h.toString : (radix?: number | undefined) => string
+>config.h : number
+>config : Record<string, number>
+>h : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.i !== undefined && { i: config.i.toString() },
+>config.i !== undefined && { i: config.i.toString() } : false | { i: string; }
+>config.i !== undefined : boolean
+>config.i : number
+>config : Record<string, number>
+>i : number
+>undefined : undefined
+>{ i: config.i.toString() } : { i: string; }
+>i : string
+>config.i.toString() : string
+>config.i.toString : (radix?: number | undefined) => string
+>config.i : number
+>config : Record<string, number>
+>i : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.j !== undefined && { j: config.j.toString() },
+>config.j !== undefined && { j: config.j.toString() } : false | { j: string; }
+>config.j !== undefined : boolean
+>config.j : number
+>config : Record<string, number>
+>j : number
+>undefined : undefined
+>{ j: config.j.toString() } : { j: string; }
+>j : string
+>config.j.toString() : string
+>config.j.toString : (radix?: number | undefined) => string
+>config.j : number
+>config : Record<string, number>
+>j : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.k !== undefined && { k: config.k.toString() },
+>config.k !== undefined && { k: config.k.toString() } : false | { k: string; }
+>config.k !== undefined : boolean
+>config.k : number
+>config : Record<string, number>
+>k : number
+>undefined : undefined
+>{ k: config.k.toString() } : { k: string; }
+>k : string
+>config.k.toString() : string
+>config.k.toString : (radix?: number | undefined) => string
+>config.k : number
+>config : Record<string, number>
+>k : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.l !== undefined && { l: config.l.toString() },
+>config.l !== undefined && { l: config.l.toString() } : false | { l: string; }
+>config.l !== undefined : boolean
+>config.l : number
+>config : Record<string, number>
+>l : number
+>undefined : undefined
+>{ l: config.l.toString() } : { l: string; }
+>l : string
+>config.l.toString() : string
+>config.l.toString : (radix?: number | undefined) => string
+>config.l : number
+>config : Record<string, number>
+>l : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.m !== undefined && { m: config.m.toString() },
+>config.m !== undefined && { m: config.m.toString() } : false | { m: string; }
+>config.m !== undefined : boolean
+>config.m : number
+>config : Record<string, number>
+>m : number
+>undefined : undefined
+>{ m: config.m.toString() } : { m: string; }
+>m : string
+>config.m.toString() : string
+>config.m.toString : (radix?: number | undefined) => string
+>config.m : number
+>config : Record<string, number>
+>m : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.n !== undefined && { n: config.n.toString() },
+>config.n !== undefined && { n: config.n.toString() } : false | { n: string; }
+>config.n !== undefined : boolean
+>config.n : number
+>config : Record<string, number>
+>n : number
+>undefined : undefined
+>{ n: config.n.toString() } : { n: string; }
+>n : string
+>config.n.toString() : string
+>config.n.toString : (radix?: number | undefined) => string
+>config.n : number
+>config : Record<string, number>
+>n : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.o !== undefined && { o: config.o.toString() },
+>config.o !== undefined && { o: config.o.toString() } : false | { o: string; }
+>config.o !== undefined : boolean
+>config.o : number
+>config : Record<string, number>
+>o : number
+>undefined : undefined
+>{ o: config.o.toString() } : { o: string; }
+>o : string
+>config.o.toString() : string
+>config.o.toString : (radix?: number | undefined) => string
+>config.o : number
+>config : Record<string, number>
+>o : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.p !== undefined && { p: config.p.toString() },
+>config.p !== undefined && { p: config.p.toString() } : false | { p: string; }
+>config.p !== undefined : boolean
+>config.p : number
+>config : Record<string, number>
+>p : number
+>undefined : undefined
+>{ p: config.p.toString() } : { p: string; }
+>p : string
+>config.p.toString() : string
+>config.p.toString : (radix?: number | undefined) => string
+>config.p : number
+>config : Record<string, number>
+>p : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.q !== undefined && { q: config.q.toString() },
+>config.q !== undefined && { q: config.q.toString() } : false | { q: string; }
+>config.q !== undefined : boolean
+>config.q : number
+>config : Record<string, number>
+>q : number
+>undefined : undefined
+>{ q: config.q.toString() } : { q: string; }
+>q : string
+>config.q.toString() : string
+>config.q.toString : (radix?: number | undefined) => string
+>config.q : number
+>config : Record<string, number>
+>q : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.r !== undefined && { r: config.r.toString() },
+>config.r !== undefined && { r: config.r.toString() } : false | { r: string; }
+>config.r !== undefined : boolean
+>config.r : number
+>config : Record<string, number>
+>r : number
+>undefined : undefined
+>{ r: config.r.toString() } : { r: string; }
+>r : string
+>config.r.toString() : string
+>config.r.toString : (radix?: number | undefined) => string
+>config.r : number
+>config : Record<string, number>
+>r : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.s !== undefined && { s: config.s.toString() },
+>config.s !== undefined && { s: config.s.toString() } : false | { s: string; }
+>config.s !== undefined : boolean
+>config.s : number
+>config : Record<string, number>
+>s : number
+>undefined : undefined
+>{ s: config.s.toString() } : { s: string; }
+>s : string
+>config.s.toString() : string
+>config.s.toString : (radix?: number | undefined) => string
+>config.s : number
+>config : Record<string, number>
+>s : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.t !== undefined && { t: config.t.toString() },
+>config.t !== undefined && { t: config.t.toString() } : false | { t: string; }
+>config.t !== undefined : boolean
+>config.t : number
+>config : Record<string, number>
+>t : number
+>undefined : undefined
+>{ t: config.t.toString() } : { t: string; }
+>t : string
+>config.t.toString() : string
+>config.t.toString : (radix?: number | undefined) => string
+>config.t : number
+>config : Record<string, number>
+>t : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.u !== undefined && { u: config.u.toString() },
+>config.u !== undefined && { u: config.u.toString() } : false | { u: string; }
+>config.u !== undefined : boolean
+>config.u : number
+>config : Record<string, number>
+>u : number
+>undefined : undefined
+>{ u: config.u.toString() } : { u: string; }
+>u : string
+>config.u.toString() : string
+>config.u.toString : (radix?: number | undefined) => string
+>config.u : number
+>config : Record<string, number>
+>u : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.v !== undefined && { v: config.v.toString() },
+>config.v !== undefined && { v: config.v.toString() } : false | { v: string; }
+>config.v !== undefined : boolean
+>config.v : number
+>config : Record<string, number>
+>v : number
+>undefined : undefined
+>{ v: config.v.toString() } : { v: string; }
+>v : string
+>config.v.toString() : string
+>config.v.toString : (radix?: number | undefined) => string
+>config.v : number
+>config : Record<string, number>
+>v : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.w !== undefined && { w: config.w.toString() },
+>config.w !== undefined && { w: config.w.toString() } : false | { w: string; }
+>config.w !== undefined : boolean
+>config.w : number
+>config : Record<string, number>
+>w : number
+>undefined : undefined
+>{ w: config.w.toString() } : { w: string; }
+>w : string
+>config.w.toString() : string
+>config.w.toString : (radix?: number | undefined) => string
+>config.w : number
+>config : Record<string, number>
+>w : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.x !== undefined && { x: config.x.toString() },
+>config.x !== undefined && { x: config.x.toString() } : false | { x: string; }
+>config.x !== undefined : boolean
+>config.x : number
+>config : Record<string, number>
+>x : number
+>undefined : undefined
+>{ x: config.x.toString() } : { x: string; }
+>x : string
+>config.x.toString() : string
+>config.x.toString : (radix?: number | undefined) => string
+>config.x : number
+>config : Record<string, number>
+>x : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.y !== undefined && { y: config.y.toString() },
+>config.y !== undefined && { y: config.y.toString() } : false | { y: string; }
+>config.y !== undefined : boolean
+>config.y : number
+>config : Record<string, number>
+>y : number
+>undefined : undefined
+>{ y: config.y.toString() } : { y: string; }
+>y : string
+>config.y.toString() : string
+>config.y.toString : (radix?: number | undefined) => string
+>config.y : number
+>config : Record<string, number>
+>y : number
+>toString : (radix?: number | undefined) => string
+
+        ...config.z !== undefined && { z: config.z.toString() }
+>config.z !== undefined && { z: config.z.toString() } : false | { z: string; }
+>config.z !== undefined : boolean
+>config.z : number
+>config : Record<string, number>
+>z : number
+>undefined : undefined
+>{ z: config.z.toString() } : { z: string; }
+>z : string
+>config.z.toString() : string
+>config.z.toString : (radix?: number | undefined) => string
+>config.z : number
+>config : Record<string, number>
+>z : number
+>toString : (radix?: number | undefined) => string
+    }
+}
+
+parseWithSpread({ a: 1, b: 2, z: 26 })
+>parseWithSpread({ a: 1, b: 2, z: 26 }) : Props
+>parseWithSpread : (config: Record<string, number>) => Props
+>{ a: 1, b: 2, z: 26 } : { a: number; b: number; z: number; }
+>a : number
+>1 : 1
+>b : number
+>2 : 2
+>z : number
+>26 : 26
+

tests/baselines/reference/spreadOfObjectLiteralAssignableToIndexSignature.types

@@ -9,11 +9,11 @@ const recordOfRecords: RecordOfRecords = {}
 >{} : {}
 
 recordOfRecords.propA = {...(foo !== undefined ? {foo} : {})} // OK
->recordOfRecords.propA = {...(foo !== undefined ? {foo} : {})} : { foo: Record<never, never>; } | {}
+>recordOfRecords.propA = {...(foo !== undefined ? {foo} : {})} : { foo?: Record<never, never>; }
 >recordOfRecords.propA : RecordOfRecords
 >recordOfRecords : RecordOfRecords
 >propA : RecordOfRecords
->{...(foo !== undefined ? {foo} : {})} : { foo: Record<never, never>; } | {}
+>{...(foo !== undefined ? {foo} : {})} : { foo?: Record<never, never>; }
 >(foo !== undefined ? {foo} : {}) : { foo: Record<never, never>; } | {}
 >foo !== undefined ? {foo} : {} : { foo: Record<never, never>; } | {}
 >foo !== undefined : boolean
@@ -36,11 +36,11 @@ recordOfRecords.propB = {...(foo && {foo})} // OK
 >foo : Record<never, never>
 
 recordOfRecords.propC = {...(foo !== undefined && {foo})} // error'd in 3.7 beta, should be OK
->recordOfRecords.propC = {...(foo !== undefined && {foo})} : { foo: Record<never, never>; } | {}
+>recordOfRecords.propC = {...(foo !== undefined && {foo})} : { foo?: Record<never, never>; }
 >recordOfRecords.propC : RecordOfRecords
 >recordOfRecords : RecordOfRecords
 >propC : RecordOfRecords
->{...(foo !== undefined && {foo})} : { foo: Record<never, never>; } | {}
+>{...(foo !== undefined && {foo})} : { foo?: Record<never, never>; }
 >(foo !== undefined && {foo}) : false | { foo: Record<never, never>; }
 >foo !== undefined && {foo} : false | { foo: Record<never, never>; }
 >foo !== undefined : boolean
@@ -55,11 +55,11 @@ const recordsOfRecordsOrEmpty: RecordOfRecordsOrEmpty = {}
 >{} : {}
 
 recordsOfRecordsOrEmpty.propA = {...(foo !== undefined ? {foo} : {})} // OK
->recordsOfRecordsOrEmpty.propA = {...(foo !== undefined ? {foo} : {})} : { foo: Record<never, never>; } | {}
+>recordsOfRecordsOrEmpty.propA = {...(foo !== undefined ? {foo} : {})} : { foo?: Record<never, never>; }
 >recordsOfRecordsOrEmpty.propA : {} | RecordOfRecordsOrEmpty
 >recordsOfRecordsOrEmpty : RecordOfRecordsOrEmpty
 >propA : {} | RecordOfRecordsOrEmpty
->{...(foo !== undefined ? {foo} : {})} : { foo: Record<never, never>; } | {}
+>{...(foo !== undefined ? {foo} : {})} : { foo?: Record<never, never>; }
 >(foo !== undefined ? {foo} : {}) : { foo: Record<never, never>; } | {}
 >foo !== undefined ? {foo} : {} : { foo: Record<never, never>; } | {}
 >foo !== undefined : boolean
@@ -82,11 +82,11 @@ recordsOfRecordsOrEmpty.propB = {...(foo && {foo})} // OK
 >foo : Record<never, never>
 
 recordsOfRecordsOrEmpty.propC = {...(foo !== undefined && {foo})} // OK
->recordsOfRecordsOrEmpty.propC = {...(foo !== undefined && {foo})} : { foo: Record<never, never>; } | {}
+>recordsOfRecordsOrEmpty.propC = {...(foo !== undefined && {foo})} : { foo?: Record<never, never>; }
 >recordsOfRecordsOrEmpty.propC : {} | RecordOfRecordsOrEmpty
 >recordsOfRecordsOrEmpty : RecordOfRecordsOrEmpty
 >propC : {} | RecordOfRecordsOrEmpty
->{...(foo !== undefined && {foo})} : { foo: Record<never, never>; } | {}
+>{...(foo !== undefined && {foo})} : { foo?: Record<never, never>; }
 >(foo !== undefined && {foo}) : false | { foo: Record<never, never>; }
 >foo !== undefined && {foo} : false | { foo: Record<never, never>; }
 >foo !== undefined : boolean

tests/baselines/reference/spreadUnion2.errors.txt

@@ -1,9 +1,9 @@
-tests/cases/conformance/types/spread/spreadUnion2.ts(5,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o1' must be of type '{} | { a: number; }', but here has type '{}'.
-tests/cases/conformance/types/spread/spreadUnion2.ts(8,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o2' must be of type '{} | { b: number; }', but here has type '{}'.
-tests/cases/conformance/types/spread/spreadUnion2.ts(11,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o3' must be of type '{} | { a: number; } | { b: number; } | { a: number; b: number; }', but here has type '{}'.
-tests/cases/conformance/types/spread/spreadUnion2.ts(12,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o3' must be of type '{} | { a: number; } | { b: number; } | { a: number; b: number; }', but here has type '{}'.
-tests/cases/conformance/types/spread/spreadUnion2.ts(15,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o4' must be of type '{} | { a: number; }', but here has type '{}'.
-tests/cases/conformance/types/spread/spreadUnion2.ts(18,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o5' must be of type '{} | { b: number; }', but here has type '{}'.
+tests/cases/conformance/types/spread/spreadUnion2.ts(5,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o1' must be of type '{} | { a: number; }', but here has type '{ a?: number; }'.
+tests/cases/conformance/types/spread/spreadUnion2.ts(8,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o2' must be of type '{} | { b: number; }', but here has type '{ b?: number; }'.
+tests/cases/conformance/types/spread/spreadUnion2.ts(11,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o3' must be of type '{} | { a: number; } | { b: number; } | { a: number; b: number; }', but here has type '{ b?: number; a?: number; }'.
+tests/cases/conformance/types/spread/spreadUnion2.ts(12,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o3' must be of type '{} | { a: number; } | { b: number; } | { a: number; b: number; }', but here has type '{ a?: number; b?: number; }'.
+tests/cases/conformance/types/spread/spreadUnion2.ts(15,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o4' must be of type '{} | { a: number; }', but here has type '{ a?: number; }'.
+tests/cases/conformance/types/spread/spreadUnion2.ts(18,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'o5' must be of type '{} | { b: number; }', but here has type '{ b?: number; }'.
 
 
 ==== tests/cases/conformance/types/spread/spreadUnion2.ts (6 errors) ====
@@ -13,35 +13,35 @@ tests/cases/conformance/types/spread/spreadUnion2.ts(18,5): error TS2403: Subseq
     var o1: {} | { a: number };
     var o1 = { ...undefinedUnion };
         ~~
-!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o1' must be of type '{} | { a: number; }', but here has type '{}'.
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o1' must be of type '{} | { a: number; }', but here has type '{ a?: number; }'.
 !!! related TS6203 tests/cases/conformance/types/spread/spreadUnion2.ts:4:5: 'o1' was also declared here.
     
     var o2: {} | { b: number };
     var o2 = { ...nullUnion };
         ~~
-!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o2' must be of type '{} | { b: number; }', but here has type '{}'.
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o2' must be of type '{} | { b: number; }', but here has type '{ b?: number; }'.
 !!! related TS6203 tests/cases/conformance/types/spread/spreadUnion2.ts:7:5: 'o2' was also declared here.
     
     var o3: {} | { a: number } | { b: number } | { a: number, b: number };
     var o3 = { ...undefinedUnion, ...nullUnion };
         ~~
-!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o3' must be of type '{} | { a: number; } | { b: number; } | { a: number; b: number; }', but here has type '{}'.
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o3' must be of type '{} | { a: number; } | { b: number; } | { a: number; b: number; }', but here has type '{ b?: number; a?: number; }'.
 !!! related TS6203 tests/cases/conformance/types/spread/spreadUnion2.ts:10:5: 'o3' was also declared here.
     var o3 = { ...nullUnion, ...undefinedUnion };
         ~~
-!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o3' must be of type '{} | { a: number; } | { b: number; } | { a: number; b: number; }', but here has type '{}'.
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o3' must be of type '{} | { a: number; } | { b: number; } | { a: number; b: number; }', but here has type '{ a?: number; b?: number; }'.
 !!! related TS6203 tests/cases/conformance/types/spread/spreadUnion2.ts:10:5: 'o3' was also declared here.
     
     var o4: {} | { a: number };
     var o4 = { ...undefinedUnion, ...undefinedUnion };
         ~~
-!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o4' must be of type '{} | { a: number; }', but here has type '{}'.
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o4' must be of type '{} | { a: number; }', but here has type '{ a?: number; }'.
 !!! related TS6203 tests/cases/conformance/types/spread/spreadUnion2.ts:14:5: 'o4' was also declared here.
     
     var o5: {} | { b: number };
     var o5 = { ...nullUnion, ...nullUnion };
         ~~
-!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o5' must be of type '{} | { b: number; }', but here has type '{}'.
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'o5' must be of type '{} | { b: number; }', but here has type '{ b?: number; }'.
 !!! related TS6203 tests/cases/conformance/types/spread/spreadUnion2.ts:17:5: 'o5' was also declared here.
     
     

tests/baselines/reference/spreadUnion2.types

@@ -14,7 +14,7 @@ var o1: {} | { a: number };
 
 var o1 = { ...undefinedUnion };
 >o1 : {} | { a: number; }
->{ ...undefinedUnion } : {} | { a: number; }
+>{ ...undefinedUnion } : { a?: number; }
 >undefinedUnion : { a: number; } | undefined
 
 var o2: {} | { b: number };
@@ -23,7 +23,7 @@ var o2: {} | { b: number };
 
 var o2 = { ...nullUnion };
 >o2 : {} | { b: number; }
->{ ...nullUnion } : {} | { b: number; }
+>{ ...nullUnion } : { b?: number; }
 >nullUnion : { b: number; } | null
 
 var o3: {} | { a: number } | { b: number } | { a: number, b: number };
@@ -35,13 +35,13 @@ var o3: {} | { a: number } | { b: number } | { a: number, b: number };
 
 var o3 = { ...undefinedUnion, ...nullUnion };
 >o3 : {} | { a: number; } | { b: number; } | { a: number; b: number; }
->{ ...undefinedUnion, ...nullUnion } : {} | { b: number; } | { a: number; } | { b: number; a: number; }
+>{ ...undefinedUnion, ...nullUnion } : { b?: number; a?: number; }
 >undefinedUnion : { a: number; } | undefined
 >nullUnion : { b: number; } | null
 
 var o3 = { ...nullUnion, ...undefinedUnion };
 >o3 : {} | { a: number; } | { b: number; } | { a: number; b: number; }
->{ ...nullUnion, ...undefinedUnion } : {} | { a: number; } | { b: number; } | { a: number; b: number; }
+>{ ...nullUnion, ...undefinedUnion } : { a?: number; b?: number; }
 >nullUnion : { b: number; } | null
 >undefinedUnion : { a: number; } | undefined
 
@@ -51,7 +51,7 @@ var o4: {} | { a: number };
 
 var o4 = { ...undefinedUnion, ...undefinedUnion };
 >o4 : {} | { a: number; }
->{ ...undefinedUnion, ...undefinedUnion } : {} | { a: number; } | { a: number; } | { a: number; }
+>{ ...undefinedUnion, ...undefinedUnion } : { a?: number; }
 >undefinedUnion : { a: number; } | undefined
 >undefinedUnion : { a: number; } | undefined
 
@@ -61,7 +61,7 @@ var o5: {} | { b: number };
 
 var o5 = { ...nullUnion, ...nullUnion };
 >o5 : {} | { b: number; }
->{ ...nullUnion, ...nullUnion } : {} | { b: number; } | { b: number; } | { b: number; }
+>{ ...nullUnion, ...nullUnion } : { b?: number; }
 >nullUnion : { b: number; } | null
 >nullUnion : { b: number; } | null
 

tests/baselines/reference/spreadUnion3.types

@@ -6,7 +6,7 @@ function f(x: { y: string } | undefined): { y: string } {
 >y : string
 
     return { y: 123, ...x } // y: string | number
->{ y: 123, ...x } : { y: number; } | { y: string; }
+>{ y: 123, ...x } : { y: string | number; }
 >y : number
 >123 : 123
 >x : { y: string; } | undefined

tests/cases/conformance/types/spread/objectSpreadRepeatedNullCheckPerf.ts

@@ -0,0 +1,62 @@
+// @strict: true
+interface Props {
+    readonly a?: string
+    readonly b?: string
+    readonly c?: string
+    readonly d?: string
+    readonly e?: string
+    readonly f?: string
+    readonly g?: string
+    readonly h?: string
+    readonly i?: string
+    readonly j?: string
+    readonly k?: string
+    readonly l?: string
+    readonly m?: string
+    readonly n?: string
+    readonly o?: string
+    readonly p?: string
+    readonly q?: string
+    readonly r?: string
+    readonly s?: string
+    readonly t?: string
+    readonly u?: string
+    readonly v?: string
+    readonly w?: string
+    readonly x?: string
+    readonly y?: string
+    readonly z?: string
+}
+
+function parseWithSpread(config: Record<string, number>): Props {
+    return {
+        ...config.a !== undefined && { a: config.a.toString() },
+        ...config.b !== undefined && { b: config.b.toString() },
+        ...config.c !== undefined && { c: config.c.toString() },
+        ...config.d !== undefined && { d: config.d.toString() },
+        ...config.e !== undefined && { e: config.e.toString() },
+        ...config.f !== undefined && { f: config.f.toString() },
+        ...config.g !== undefined && { g: config.g.toString() },
+        ...config.h !== undefined && { h: config.h.toString() },
+        ...config.i !== undefined && { i: config.i.toString() },
+        ...config.j !== undefined && { j: config.j.toString() },
+        ...config.k !== undefined && { k: config.k.toString() },
+        ...config.l !== undefined && { l: config.l.toString() },
+        ...config.m !== undefined && { m: config.m.toString() },
+        ...config.n !== undefined && { n: config.n.toString() },
+        ...config.o !== undefined && { o: config.o.toString() },
+        ...config.p !== undefined && { p: config.p.toString() },
+        ...config.q !== undefined && { q: config.q.toString() },
+        ...config.r !== undefined && { r: config.r.toString() },
+        ...config.s !== undefined && { s: config.s.toString() },
+        ...config.t !== undefined && { t: config.t.toString() },
+        ...config.u !== undefined && { u: config.u.toString() },
+        ...config.v !== undefined && { v: config.v.toString() },
+        ...config.w !== undefined && { w: config.w.toString() },
+        ...config.x !== undefined && { x: config.x.toString() },
+        ...config.y !== undefined && { y: config.y.toString() },
+        ...config.z !== undefined && { z: config.z.toString() }
+    }
+}
+
+parseWithSpread({ a: 1, b: 2, z: 26 })