fix(40617): handle uninitialized class member with computed key (#45974)

src/compiler/binder.ts

@@ -889,7 +889,7 @@ namespace ts {
             return isDottedName(expr)
                 || (isPropertyAccessExpression(expr) || isNonNullExpression(expr) || isParenthesizedExpression(expr)) && isNarrowableReference(expr.expression)
                 || isBinaryExpression(expr) && expr.operatorToken.kind === SyntaxKind.CommaToken && isNarrowableReference(expr.right)
-                || isElementAccessExpression(expr) && isStringOrNumericLiteralLike(expr.argumentExpression) && isNarrowableReference(expr.expression)
+                || isElementAccessExpression(expr) && (isStringOrNumericLiteralLike(expr.argumentExpression) || isEntityNameExpression(expr.argumentExpression)) && isNarrowableReference(expr.expression)
                 || isAssignmentExpression(expr) && isNarrowableReference(expr.left);
         }
 

src/compiler/checker.ts

@@ -22877,9 +22877,10 @@ namespace ts {
                     return isMatchingReference((source as NonNullExpression | ParenthesizedExpression).expression, target);
                 case SyntaxKind.PropertyAccessExpression:
                 case SyntaxKind.ElementAccessExpression:
-                    return isAccessExpression(target) &&
-                        getAccessedPropertyName(source as AccessExpression) === getAccessedPropertyName(target) &&
-                        isMatchingReference((source as AccessExpression).expression, target.expression);
+                    const sourcePropertyName = getAccessedPropertyName(source as AccessExpression);
+                    const targetPropertyName = isAccessExpression(target) ? getAccessedPropertyName(target) : undefined;
+                    return sourcePropertyName !== undefined && targetPropertyName !== undefined && targetPropertyName === sourcePropertyName &&
+                        isMatchingReference((source as AccessExpression).expression, (target as AccessExpression).expression);
                 case SyntaxKind.QualifiedName:
                     return isAccessExpression(target) &&
                         (source as QualifiedName).right.escapedText === getAccessedPropertyName(target) &&
@@ -22891,12 +22892,52 @@ namespace ts {
         }
 
         function getAccessedPropertyName(access: AccessExpression | BindingElement | ParameterDeclaration): __String | undefined {
-            let propertyName;
-            return access.kind === SyntaxKind.PropertyAccessExpression ? access.name.escapedText :
-                access.kind === SyntaxKind.ElementAccessExpression && isStringOrNumericLiteralLike(access.argumentExpression) ? escapeLeadingUnderscores(access.argumentExpression.text) :
-                access.kind === SyntaxKind.BindingElement && (propertyName = getDestructuringPropertyName(access)) ? escapeLeadingUnderscores(propertyName) :
-                access.kind === SyntaxKind.Parameter ? ("" + access.parent.parameters.indexOf(access)) as __String :
-                undefined;
+            if (isPropertyAccessExpression(access)) {
+                return access.name.escapedText;
+            }
+            if (isElementAccessExpression(access)) {
+                return tryGetElementAccessExpressionName(access);
+            }
+            if (isBindingElement(access)) {
+                const name = getDestructuringPropertyName(access);
+                return name ? escapeLeadingUnderscores(name) : undefined;
+            }
+            if (isParameter(access)) {
+                return ("" + access.parent.parameters.indexOf(access)) as __String;
+            }
+            return undefined;
+        }
+
+        function tryGetNameFromType(type: Type) {
+            return type.flags & TypeFlags.UniqueESSymbol ? (type as UniqueESSymbolType).escapedName :
+                type.flags & TypeFlags.StringOrNumberLiteral ? escapeLeadingUnderscores("" + (type as StringLiteralType | NumberLiteralType).value) : undefined;
+        }
+
+        function tryGetElementAccessExpressionName(node: ElementAccessExpression) {
+            if (isStringOrNumericLiteralLike(node.argumentExpression)) {
+                return escapeLeadingUnderscores(node.argumentExpression.text);
+            }
+            if (isEntityNameExpression(node.argumentExpression)) {
+                const symbol = resolveEntityName(node.argumentExpression, SymbolFlags.Value, /*ignoreErrors*/ true);
+                if (!symbol || !isConstVariable(symbol)) return undefined;
+
+                const declaration = symbol.valueDeclaration;
+                if (declaration === undefined) return undefined;
+
+                const type = tryGetTypeFromEffectiveTypeNode(declaration);
+                if (type) {
+                    const name = tryGetNameFromType(type);
+                    if (name !== undefined) {
+                        return name;
+                    }
+                }
+
+                if (hasOnlyExpressionInitializer(declaration)) {
+                    const initializer = getEffectiveInitializer(declaration);
+                    return initializer && tryGetNameFromType(getTypeOfExpression(initializer));
+                }
+            }
+            return undefined;
         }
 
         function containsMatchingReference(source: Node, target: Node) {
@@ -39529,7 +39570,7 @@ namespace ts {
                 }
                 if (!isStatic(member) && isPropertyWithoutInitializer(member)) {
                     const propName = (member as PropertyDeclaration).name;
-                    if (isIdentifier(propName) || isPrivateIdentifier(propName)) {
+                    if (isIdentifier(propName) || isPrivateIdentifier(propName) || isComputedPropertyName(propName)) {
                         const type = getTypeOfSymbol(getSymbolOfNode(member));
                         if (!(type.flags & TypeFlags.AnyOrUnknown || getFalsyFlags(type) & TypeFlags.Undefined)) {
                             if (!constructor || !isPropertyInitializedInConstructor(propName, type, constructor)) {
@@ -39565,8 +39606,10 @@ namespace ts {
             return false;
         }
 
-        function isPropertyInitializedInConstructor(propName: Identifier | PrivateIdentifier, propType: Type, constructor: ConstructorDeclaration) {
-            const reference = factory.createPropertyAccessExpression(factory.createThis(), propName);
+        function isPropertyInitializedInConstructor(propName: Identifier | PrivateIdentifier | ComputedPropertyName, propType: Type, constructor: ConstructorDeclaration) {
+            const reference = isComputedPropertyName(propName)
+                ? factory.createElementAccessExpression(factory.createThis(), propName.expression)
+                : factory.createPropertyAccessExpression(factory.createThis(), propName);
             setParent(reference.expression, reference);
             setParent(reference, constructor);
             reference.flowNode = constructor.returnFlowNode;

src/compiler/commandLineParser.ts

@@ -2755,7 +2755,7 @@ namespace ts {
         function getPropFromRaw<T>(prop: "files" | "include" | "exclude" | "references", validateElement: (value: unknown) => boolean, elementTypeName: string): PropOfRaw<T> {
             if (hasProperty(raw, prop) && !isNullOrUndefined(raw[prop])) {
                 if (isArray(raw[prop])) {
-                    const result = raw[prop];
+                    const result = raw[prop] as T[];
                     if (!sourceFile && !every(result, validateElement)) {
                         errors.push(createCompilerDiagnostic(Diagnostics.Compiler_option_0_requires_a_value_of_type_1, prop, elementTypeName));
                     }

tests/baselines/reference/incrementOnNullAssertion.types

@@ -27,21 +27,21 @@ if (foo[x] === undefined) {
 }
 else {
     let nu = foo[x]
->nu : number | undefined
->foo[x] : number | undefined
+>nu : number
+>foo[x] : number
 >foo : Dictionary<number>
 >x : "bar"
 
     let n = foo[x]
->n : number | undefined
->foo[x] : number | undefined
+>n : number
+>foo[x] : number
 >foo : Dictionary<number>
 >x : "bar"
 
     foo[x]!++
 >foo[x]!++ : number
 >foo[x]! : number
->foo[x] : number | undefined
+>foo[x] : number
 >foo : Dictionary<number>
 >x : "bar"
 }

tests/baselines/reference/strictPropertyInitialization.errors.txt

@@ -164,4 +164,19 @@ tests/cases/conformance/classes/propertyMemberDeclarations/strictPropertyInitial
             this.#b = someValue();
         }
     }
+    
+    const a = 'a';
+    const b = Symbol();
+    
+    class C12 {
+        [a]: number;
+        [b]: number;
+        ['c']: number;
+    
+        constructor() {
+            this[a] = 1;
+            this[b] = 1;
+            this['c'] = 1;
+        }
+    }
     

tests/baselines/reference/strictPropertyInitialization.js

@@ -132,6 +132,21 @@ class C11 {
         this.#b = someValue();
     }
 }
+
+const a = 'a';
+const b = Symbol();
+
+class C12 {
+    [a]: number;
+    [b]: number;
+    ['c']: number;
+
+    constructor() {
+        this[a] = 1;
+        this[b] = 1;
+        this['c'] = 1;
+    }
+}
 
 
 //// [strictPropertyInitialization.js]
@@ -235,6 +250,15 @@ class C11 {
     }
 }
 _C11_b = new WeakMap();
+const a = 'a';
+const b = Symbol();
+class C12 {
+    constructor() {
+        this[a] = 1;
+        this[b] = 1;
+        this['c'] = 1;
+    }
+}
 
 
 //// [strictPropertyInitialization.d.ts]
@@ -303,3 +327,11 @@ declare class C11 {
     a: number;
     constructor();
 }
+declare const a = "a";
+declare const b: unique symbol;
+declare class C12 {
+    [a]: number;
+    [b]: number;
+    ['c']: number;
+    constructor();
+}

tests/baselines/reference/strictPropertyInitialization.symbols

@@ -311,3 +311,40 @@ class C11 {
     }
 }
 
+const a = 'a';
+>a : Symbol(a, Decl(strictPropertyInitialization.ts, 134, 5))
+
+const b = Symbol();
+>b : Symbol(b, Decl(strictPropertyInitialization.ts, 135, 5))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+
+class C12 {
+>C12 : Symbol(C12, Decl(strictPropertyInitialization.ts, 135, 19))
+
+    [a]: number;
+>[a] : Symbol(C12[a], Decl(strictPropertyInitialization.ts, 137, 11))
+>a : Symbol(a, Decl(strictPropertyInitialization.ts, 134, 5))
+
+    [b]: number;
+>[b] : Symbol(C12[b], Decl(strictPropertyInitialization.ts, 138, 16))
+>b : Symbol(b, Decl(strictPropertyInitialization.ts, 135, 5))
+
+    ['c']: number;
+>['c'] : Symbol(C12['c'], Decl(strictPropertyInitialization.ts, 139, 16))
+>'c' : Symbol(C12['c'], Decl(strictPropertyInitialization.ts, 139, 16))
+
+    constructor() {
+        this[a] = 1;
+>this : Symbol(C12, Decl(strictPropertyInitialization.ts, 135, 19))
+>a : Symbol(a, Decl(strictPropertyInitialization.ts, 134, 5))
+
+        this[b] = 1;
+>this : Symbol(C12, Decl(strictPropertyInitialization.ts, 135, 19))
+>b : Symbol(b, Decl(strictPropertyInitialization.ts, 135, 5))
+
+        this['c'] = 1;
+>this : Symbol(C12, Decl(strictPropertyInitialization.ts, 135, 19))
+>'c' : Symbol(C12['c'], Decl(strictPropertyInitialization.ts, 139, 16))
+    }
+}
+

tests/baselines/reference/strictPropertyInitialization.types

@@ -347,3 +347,51 @@ class C11 {
     }
 }
 
+const a = 'a';
+>a : "a"
+>'a' : "a"
+
+const b = Symbol();
+>b : unique symbol
+>Symbol() : unique symbol
+>Symbol : SymbolConstructor
+
+class C12 {
+>C12 : C12
+
+    [a]: number;
+>[a] : number
+>a : "a"
+
+    [b]: number;
+>[b] : number
+>b : unique symbol
+
+    ['c']: number;
+>['c'] : number
+>'c' : "c"
+
+    constructor() {
+        this[a] = 1;
+>this[a] = 1 : 1
+>this[a] : number
+>this : this
+>a : "a"
+>1 : 1
+
+        this[b] = 1;
+>this[b] = 1 : 1
+>this[b] : number
+>this : this
+>b : unique symbol
+>1 : 1
+
+        this['c'] = 1;
+>this['c'] = 1 : 1
+>this['c'] : number
+>this : this
+>'c' : "c"
+>1 : 1
+    }
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty1.js

@@ -1,4 +1,4 @@
-//// [typeGuardNarrowsIndexedAccessOfKnownProperty.ts]
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty1.ts]
 interface Square {
     ["dash-ok"]: "square";
     ["square-size"]: number;
@@ -80,7 +80,7 @@ export function g(pair: [number, string?]): string {
 }
 
 
-//// [typeGuardNarrowsIndexedAccessOfKnownProperty.js]
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty1.js]
 "use strict";
 exports.__esModule = true;
 exports.g = void 0;

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty1.symbols

@@ -1,254 +1,254 @@
-=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty.ts ===
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty1.ts ===
 interface Square {
->Square : Symbol(Square, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 0, 0))
+>Square : Symbol(Square, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 0, 0))
 
     ["dash-ok"]: "square";
->["dash-ok"] : Symbol(Square["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 0, 18))
->"dash-ok" : Symbol(Square["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 0, 18))
+>["dash-ok"] : Symbol(Square["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 0, 18))
+>"dash-ok" : Symbol(Square["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 0, 18))
 
     ["square-size"]: number;
->["square-size"] : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 1, 26))
->"square-size" : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 1, 26))
+>["square-size"] : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 1, 26))
+>"square-size" : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 1, 26))
 }
  interface Rectangle {
->Rectangle : Symbol(Rectangle, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 3, 1))
+>Rectangle : Symbol(Rectangle, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 3, 1))
 
     ["dash-ok"]: "rectangle";
->["dash-ok"] : Symbol(Rectangle["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 4, 22))
->"dash-ok" : Symbol(Rectangle["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 4, 22))
+>["dash-ok"] : Symbol(Rectangle["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 4, 22))
+>"dash-ok" : Symbol(Rectangle["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 4, 22))
 
     width: number;
->width : Symbol(Rectangle.width, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 5, 29))
+>width : Symbol(Rectangle.width, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 5, 29))
 
     height: number;
->height : Symbol(Rectangle.height, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 6, 18))
+>height : Symbol(Rectangle.height, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 6, 18))
 }
  interface Circle {
->Circle : Symbol(Circle, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 8, 1))
+>Circle : Symbol(Circle, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 8, 1))
 
     ["dash-ok"]: "circle";
->["dash-ok"] : Symbol(Circle["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 9, 19))
->"dash-ok" : Symbol(Circle["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 9, 19))
+>["dash-ok"] : Symbol(Circle["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 9, 19))
+>"dash-ok" : Symbol(Circle["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 9, 19))
 
     radius: number;
->radius : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 10, 26))
+>radius : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 10, 26))
 }
  type Shape = Square | Rectangle | Circle;
->Shape : Symbol(Shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 12, 1))
->Square : Symbol(Square, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 0, 0))
->Rectangle : Symbol(Rectangle, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 3, 1))
->Circle : Symbol(Circle, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 8, 1))
+>Shape : Symbol(Shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 12, 1))
+>Square : Symbol(Square, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 0, 0))
+>Rectangle : Symbol(Rectangle, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 3, 1))
+>Circle : Symbol(Circle, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 8, 1))
 
 interface Subshape {
->Subshape : Symbol(Subshape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 13, 42))
+>Subshape : Symbol(Subshape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 13, 42))
 
     "0": {
->"0" : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 14, 20))
+>"0" : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 14, 20))
 
         sub: {
->sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 15, 10))
+>sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 15, 10))
 
             under: {
->under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
+>under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
 
                 shape: Shape;
->shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 17, 20))
->Shape : Symbol(Shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 12, 1))
+>shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 17, 20))
+>Shape : Symbol(Shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 12, 1))
             }
         }
     }
 }
 function area(s: Shape): number {
->area : Symbol(area, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 22, 1))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 23, 14))
->Shape : Symbol(Shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 12, 1))
+>area : Symbol(area, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 22, 1))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 23, 14))
+>Shape : Symbol(Shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 12, 1))
 
     switch(s['dash-ok']) {
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 23, 14))
->'dash-ok' : Symbol(["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 0, 18), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 4, 22), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 9, 19))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 23, 14))
+>'dash-ok' : Symbol(["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 0, 18), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 4, 22), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 9, 19))
 
         case "square": return s['square-size'] * s['square-size'];
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 23, 14))
->'square-size' : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 1, 26))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 23, 14))
->'square-size' : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 1, 26))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 23, 14))
+>'square-size' : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 1, 26))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 23, 14))
+>'square-size' : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 1, 26))
 
         case "rectangle": return s.width * s['height'];
->s.width : Symbol(Rectangle.width, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 5, 29))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 23, 14))
->width : Symbol(Rectangle.width, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 5, 29))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 23, 14))
->'height' : Symbol(Rectangle.height, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 6, 18))
+>s.width : Symbol(Rectangle.width, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 5, 29))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 23, 14))
+>width : Symbol(Rectangle.width, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 5, 29))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 23, 14))
+>'height' : Symbol(Rectangle.height, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 6, 18))
 
         case "circle": return Math.PI * s['radius'] * s.radius;
 >Math.PI : Symbol(Math.PI, Decl(lib.es5.d.ts, --, --))
 >Math : Symbol(Math, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
 >PI : Symbol(Math.PI, Decl(lib.es5.d.ts, --, --))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 23, 14))
->'radius' : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 10, 26))
->s.radius : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 10, 26))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 23, 14))
->radius : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 10, 26))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 23, 14))
+>'radius' : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 10, 26))
+>s.radius : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 10, 26))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 23, 14))
+>radius : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 10, 26))
     }
 }
 function subarea(s: Subshape): number {
->subarea : Symbol(subarea, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 29, 1))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 30, 17))
->Subshape : Symbol(Subshape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 13, 42))
+>subarea : Symbol(subarea, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 29, 1))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 30, 17))
+>Subshape : Symbol(Subshape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 13, 42))
 
     switch(s[0]["sub"].under["shape"]["dash-ok"]) {
->s[0]["sub"].under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 30, 17))
->0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 14, 20))
->"sub" : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 15, 10))
->under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->"shape" : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 17, 20))
->"dash-ok" : Symbol(["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 0, 18), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 4, 22), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 9, 19))
+>s[0]["sub"].under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 30, 17))
+>0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 14, 20))
+>"sub" : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 15, 10))
+>under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>"shape" : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 17, 20))
+>"dash-ok" : Symbol(["dash-ok"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 0, 18), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 4, 22), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 9, 19))
 
         case "square": return s[0].sub.under.shape["square-size"] * s[0].sub.under.shape["square-size"];
->s[0].sub.under.shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 17, 20))
->s[0].sub.under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->s[0].sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 15, 10))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 30, 17))
->0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 14, 20))
->sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 15, 10))
->under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 17, 20))
->"square-size" : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 1, 26))
->s[0].sub.under.shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 17, 20))
->s[0].sub.under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->s[0].sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 15, 10))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 30, 17))
->0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 14, 20))
->sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 15, 10))
->under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 17, 20))
->"square-size" : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 1, 26))
+>s[0].sub.under.shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 17, 20))
+>s[0].sub.under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>s[0].sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 15, 10))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 30, 17))
+>0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 14, 20))
+>sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 15, 10))
+>under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 17, 20))
+>"square-size" : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 1, 26))
+>s[0].sub.under.shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 17, 20))
+>s[0].sub.under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>s[0].sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 15, 10))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 30, 17))
+>0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 14, 20))
+>sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 15, 10))
+>under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 17, 20))
+>"square-size" : Symbol(Square["square-size"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 1, 26))
 
         case "rectangle": return s[0]["sub"]["under"]["shape"]["width"] * s[0]["sub"]["under"]["shape"].height;
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 30, 17))
->0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 14, 20))
->"sub" : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 15, 10))
->"under" : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->"shape" : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 17, 20))
->"width" : Symbol(Rectangle.width, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 5, 29))
->s[0]["sub"]["under"]["shape"].height : Symbol(Rectangle.height, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 6, 18))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 30, 17))
->0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 14, 20))
->"sub" : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 15, 10))
->"under" : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->"shape" : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 17, 20))
->height : Symbol(Rectangle.height, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 6, 18))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 30, 17))
+>0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 14, 20))
+>"sub" : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 15, 10))
+>"under" : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>"shape" : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 17, 20))
+>"width" : Symbol(Rectangle.width, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 5, 29))
+>s[0]["sub"]["under"]["shape"].height : Symbol(Rectangle.height, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 6, 18))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 30, 17))
+>0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 14, 20))
+>"sub" : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 15, 10))
+>"under" : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>"shape" : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 17, 20))
+>height : Symbol(Rectangle.height, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 6, 18))
 
         case "circle": return Math.PI * s[0].sub.under["shape"].radius * s[0]["sub"].under.shape["radius"];
 >Math.PI : Symbol(Math.PI, Decl(lib.es5.d.ts, --, --))
 >Math : Symbol(Math, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
 >PI : Symbol(Math.PI, Decl(lib.es5.d.ts, --, --))
->s[0].sub.under["shape"].radius : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 10, 26))
->s[0].sub.under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->s[0].sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 15, 10))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 30, 17))
->0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 14, 20))
->sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 15, 10))
->under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->"shape" : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 17, 20))
->radius : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 10, 26))
->s[0]["sub"].under.shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 17, 20))
->s[0]["sub"].under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 30, 17))
->0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 14, 20))
->"sub" : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 15, 10))
->under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 16, 14))
->shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 17, 20))
->"radius" : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 10, 26))
+>s[0].sub.under["shape"].radius : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 10, 26))
+>s[0].sub.under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>s[0].sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 15, 10))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 30, 17))
+>0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 14, 20))
+>sub : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 15, 10))
+>under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>"shape" : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 17, 20))
+>radius : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 10, 26))
+>s[0]["sub"].under.shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 17, 20))
+>s[0]["sub"].under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>s : Symbol(s, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 30, 17))
+>0 : Symbol(Subshape["0"], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 14, 20))
+>"sub" : Symbol(sub, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 15, 10))
+>under : Symbol(under, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 16, 14))
+>shape : Symbol(shape, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 17, 20))
+>"radius" : Symbol(Circle.radius, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 10, 26))
     }
 }
 
 interface X {
->X : Symbol(X, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 36, 1))
+>X : Symbol(X, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 36, 1))
 
     0: "xx",
->0 : Symbol(X[0], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 38, 13))
+>0 : Symbol(X[0], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 38, 13))
 
     1: number
->1 : Symbol(X[1], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 39, 12))
+>1 : Symbol(X[1], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 39, 12))
 }
 
 interface Y {
->Y : Symbol(Y, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 41, 1))
+>Y : Symbol(Y, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 41, 1))
 
     0: "yy",
->0 : Symbol(Y[0], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 43, 13))
+>0 : Symbol(Y[0], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 43, 13))
 
     1: string
->1 : Symbol(Y[1], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 44, 12))
+>1 : Symbol(Y[1], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 44, 12))
 }
 
 type A = ["aa", number];
->A : Symbol(A, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 46, 1))
+>A : Symbol(A, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 46, 1))
 
 type B = ["bb", string];
->B : Symbol(B, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 48, 24))
+>B : Symbol(B, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 48, 24))
 
 type Z = X | Y;
->Z : Symbol(Z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 49, 24))
->X : Symbol(X, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 36, 1))
->Y : Symbol(Y, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 41, 1))
+>Z : Symbol(Z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 49, 24))
+>X : Symbol(X, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 36, 1))
+>Y : Symbol(Y, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 41, 1))
 
 type C = A | B;
->C : Symbol(C, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 51, 15))
->A : Symbol(A, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 46, 1))
->B : Symbol(B, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 48, 24))
+>C : Symbol(C, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 51, 15))
+>A : Symbol(A, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 46, 1))
+>B : Symbol(B, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 48, 24))
 
 function check(z: Z, c: C) {
->check : Symbol(check, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 53, 15))
->z : Symbol(z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 55, 15))
->Z : Symbol(Z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 49, 24))
->c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 55, 20))
->C : Symbol(C, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 51, 15))
+>check : Symbol(check, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 53, 15))
+>z : Symbol(z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 55, 15))
+>Z : Symbol(Z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 49, 24))
+>c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 55, 20))
+>C : Symbol(C, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 51, 15))
 
     z[0] // fine, typescript sees "xx" | "yy"
->z : Symbol(z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 55, 15))
->0 : Symbol(0, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 38, 13), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 43, 13))
+>z : Symbol(z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 55, 15))
+>0 : Symbol(0, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 38, 13), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 43, 13))
 
     switch (z[0]) {
->z : Symbol(z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 55, 15))
->0 : Symbol(0, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 38, 13), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 43, 13))
+>z : Symbol(z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 55, 15))
+>0 : Symbol(0, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 38, 13), Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 43, 13))
 
         case "xx":
             var xx: number = z[1] // should be number
->xx : Symbol(xx, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 59, 15))
->z : Symbol(z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 55, 15))
->1 : Symbol(X[1], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 39, 12))
+>xx : Symbol(xx, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 59, 15))
+>z : Symbol(z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 55, 15))
+>1 : Symbol(X[1], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 39, 12))
 
             break;
         case "yy":
             var yy: string = z[1] // should be string
->yy : Symbol(yy, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 62, 15))
->z : Symbol(z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 55, 15))
->1 : Symbol(Y[1], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 44, 12))
+>yy : Symbol(yy, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 62, 15))
+>z : Symbol(z, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 55, 15))
+>1 : Symbol(Y[1], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 44, 12))
 
             break;
     }
     c[0] // fine, typescript sees "xx" | "yy"
->c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 55, 20))
+>c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 55, 20))
 >0 : Symbol(0)
 
     switch (c[0]) {
->c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 55, 20))
+>c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 55, 20))
 >0 : Symbol(0)
 
         case "aa":
             var aa: number = c[1] // should be number
->aa : Symbol(aa, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 68, 15))
->c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 55, 20))
+>aa : Symbol(aa, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 68, 15))
+>c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 55, 20))
 >1 : Symbol(1)
 
             break;
         case "bb":
             var bb: string = c[1] // should be string
->bb : Symbol(bb, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 71, 15))
->c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 55, 20))
+>bb : Symbol(bb, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 71, 15))
+>c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 55, 20))
 >1 : Symbol(1)
 
             break;
@@ -256,13 +256,13 @@ function check(z: Z, c: C) {
 }
 
 export function g(pair: [number, string?]): string {
->g : Symbol(g, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 74, 1))
->pair : Symbol(pair, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 76, 18))
+>g : Symbol(g, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 74, 1))
+>pair : Symbol(pair, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 76, 18))
 
     return pair[1] ? pair[1] : 'nope';
->pair : Symbol(pair, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 76, 18))
+>pair : Symbol(pair, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 76, 18))
 >1 : Symbol(1)
->pair : Symbol(pair, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty.ts, 76, 18))
+>pair : Symbol(pair, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty1.ts, 76, 18))
 >1 : Symbol(1)
 }
 

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty1.types

@@ -1,4 +1,4 @@
-=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty.ts ===
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty1.ts ===
 interface Square {
     ["dash-ok"]: "square";
 >["dash-ok"] : "square"

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty2.js

@@ -0,0 +1,18 @@
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty2.ts]
+const foo: { key?: number } = {};
+const key = 'key' as const;
+
+if (foo[key]) {
+    foo[key]; // number
+    foo.key;  // number
+}
+
+
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty2.js]
+"use strict";
+var foo = {};
+var key = 'key';
+if (foo[key]) {
+    foo[key]; // number
+    foo.key; // number
+}

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty2.symbols

@@ -0,0 +1,23 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty2.ts ===
+const foo: { key?: number } = {};
+>foo : Symbol(foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty2.ts, 0, 5))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty2.ts, 0, 12))
+
+const key = 'key' as const;
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty2.ts, 1, 5))
+>const : Symbol(const)
+
+if (foo[key]) {
+>foo : Symbol(foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty2.ts, 0, 5))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty2.ts, 1, 5))
+
+    foo[key]; // number
+>foo : Symbol(foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty2.ts, 0, 5))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty2.ts, 1, 5))
+
+    foo.key;  // number
+>foo.key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty2.ts, 0, 12))
+>foo : Symbol(foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty2.ts, 0, 5))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty2.ts, 0, 12))
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty2.types

@@ -0,0 +1,27 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty2.ts ===
+const foo: { key?: number } = {};
+>foo : { key?: number | undefined; }
+>key : number | undefined
+>{} : {}
+
+const key = 'key' as const;
+>key : "key"
+>'key' as const : "key"
+>'key' : "key"
+
+if (foo[key]) {
+>foo[key] : number | undefined
+>foo : { key?: number | undefined; }
+>key : "key"
+
+    foo[key]; // number
+>foo[key] : number
+>foo : { key?: number | undefined; }
+>key : "key"
+
+    foo.key;  // number
+>foo.key : number
+>foo : { key?: number | undefined; }
+>key : number
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty3.js

@@ -0,0 +1,18 @@
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty3.ts]
+type Foo = (number | undefined)[] | undefined;
+
+const foo: Foo = [1, 2, 3];
+const index = 1;
+
+if (foo !== undefined && foo[index] !== undefined && foo[index] >= 0) {
+    foo[index] // number
+}
+
+
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty3.js]
+"use strict";
+var foo = [1, 2, 3];
+var index = 1;
+if (foo !== undefined && foo[index] !== undefined && foo[index] >= 0) {
+    foo[index]; // number
+}

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty3.symbols

@@ -0,0 +1,25 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty3.ts ===
+type Foo = (number | undefined)[] | undefined;
+>Foo : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty3.ts, 0, 0))
+
+const foo: Foo = [1, 2, 3];
+>foo : Symbol(foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty3.ts, 2, 5))
+>Foo : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty3.ts, 0, 0))
+
+const index = 1;
+>index : Symbol(index, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty3.ts, 3, 5))
+
+if (foo !== undefined && foo[index] !== undefined && foo[index] >= 0) {
+>foo : Symbol(foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty3.ts, 2, 5))
+>undefined : Symbol(undefined)
+>foo : Symbol(foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty3.ts, 2, 5))
+>index : Symbol(index, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty3.ts, 3, 5))
+>undefined : Symbol(undefined)
+>foo : Symbol(foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty3.ts, 2, 5))
+>index : Symbol(index, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty3.ts, 3, 5))
+
+    foo[index] // number
+>foo : Symbol(foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty3.ts, 2, 5))
+>index : Symbol(index, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty3.ts, 3, 5))
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty3.types

@@ -0,0 +1,38 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty3.ts ===
+type Foo = (number | undefined)[] | undefined;
+>Foo : Foo
+
+const foo: Foo = [1, 2, 3];
+>foo : Foo
+>[1, 2, 3] : number[]
+>1 : 1
+>2 : 2
+>3 : 3
+
+const index = 1;
+>index : 1
+>1 : 1
+
+if (foo !== undefined && foo[index] !== undefined && foo[index] >= 0) {
+>foo !== undefined && foo[index] !== undefined && foo[index] >= 0 : boolean
+>foo !== undefined && foo[index] !== undefined : boolean
+>foo !== undefined : boolean
+>foo : (number | undefined)[]
+>undefined : undefined
+>foo[index] !== undefined : boolean
+>foo[index] : number | undefined
+>foo : (number | undefined)[]
+>index : 1
+>undefined : undefined
+>foo[index] >= 0 : boolean
+>foo[index] : number
+>foo : (number | undefined)[]
+>index : 1
+>0 : 0
+
+    foo[index] // number
+>foo[index] : number
+>foo : (number | undefined)[]
+>index : 1
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty4.js

@@ -0,0 +1,28 @@
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty4.ts]
+class Foo {
+    x: number | undefined;
+
+    constructor() {
+        this.x = 5;
+
+        this.x;    // number
+        this['x']; // number
+
+        const key = 'x';
+        this[key]; // number
+    }
+}
+
+
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty4.js]
+"use strict";
+var Foo = /** @class */ (function () {
+    function Foo() {
+        this.x = 5;
+        this.x; // number
+        this['x']; // number
+        var key = 'x';
+        this[key]; // number
+    }
+    return Foo;
+}());

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty4.symbols

@@ -0,0 +1,31 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty4.ts ===
+class Foo {
+>Foo : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 0, 0))
+
+    x: number | undefined;
+>x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 0, 11))
+
+    constructor() {
+        this.x = 5;
+>this.x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 0, 11))
+>this : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 0, 0))
+>x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 0, 11))
+
+        this.x;    // number
+>this.x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 0, 11))
+>this : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 0, 0))
+>x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 0, 11))
+
+        this['x']; // number
+>this : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 0, 0))
+>'x' : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 0, 11))
+
+        const key = 'x';
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 9, 13))
+
+        this[key]; // number
+>this : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 0, 0))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty4.ts, 9, 13))
+    }
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty4.types

@@ -0,0 +1,36 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty4.ts ===
+class Foo {
+>Foo : Foo
+
+    x: number | undefined;
+>x : number | undefined
+
+    constructor() {
+        this.x = 5;
+>this.x = 5 : 5
+>this.x : number | undefined
+>this : this
+>x : number | undefined
+>5 : 5
+
+        this.x;    // number
+>this.x : number
+>this : this
+>x : number
+
+        this['x']; // number
+>this['x'] : number
+>this : this
+>'x' : "x"
+
+        const key = 'x';
+>key : "x"
+>'x' : "x"
+
+        this[key]; // number
+>this[key] : number
+>this : this
+>key : "x"
+    }
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty5.js

@@ -0,0 +1,40 @@
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty5.ts]
+const a: { key?: { x?: number } } = {};
+const aIndex = "key";
+if (a[aIndex] && a[aIndex].x) {
+    a[aIndex].x // number
+}
+
+const b: { key: { x?: number } } = { key: {} };
+const bIndex = "key";
+if (b[bIndex].x) {
+    b[bIndex].x // number
+}
+
+interface Foo {
+    x: number | undefined;
+}
+const c: Foo[] = [];
+const cIndex = 1;
+if (c[cIndex].x) {
+    c[cIndex].x // number
+}
+
+
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty5.js]
+"use strict";
+var a = {};
+var aIndex = "key";
+if (a[aIndex] && a[aIndex].x) {
+    a[aIndex].x; // number
+}
+var b = { key: {} };
+var bIndex = "key";
+if (b[bIndex].x) {
+    b[bIndex].x; // number
+}
+var c = [];
+var cIndex = 1;
+if (c[cIndex].x) {
+    c[cIndex].x; // number
+}

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty5.symbols

@@ -0,0 +1,72 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty5.ts ===
+const a: { key?: { x?: number } } = {};
+>a : Symbol(a, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 0, 5))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 0, 10))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 0, 18))
+
+const aIndex = "key";
+>aIndex : Symbol(aIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 1, 5))
+
+if (a[aIndex] && a[aIndex].x) {
+>a : Symbol(a, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 0, 5))
+>aIndex : Symbol(aIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 1, 5))
+>a[aIndex].x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 0, 18))
+>a : Symbol(a, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 0, 5))
+>aIndex : Symbol(aIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 1, 5))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 0, 18))
+
+    a[aIndex].x // number
+>a[aIndex].x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 0, 18))
+>a : Symbol(a, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 0, 5))
+>aIndex : Symbol(aIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 1, 5))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 0, 18))
+}
+
+const b: { key: { x?: number } } = { key: {} };
+>b : Symbol(b, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 6, 5))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 6, 10))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 6, 17))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 6, 36))
+
+const bIndex = "key";
+>bIndex : Symbol(bIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 7, 5))
+
+if (b[bIndex].x) {
+>b[bIndex].x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 6, 17))
+>b : Symbol(b, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 6, 5))
+>bIndex : Symbol(bIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 7, 5))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 6, 17))
+
+    b[bIndex].x // number
+>b[bIndex].x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 6, 17))
+>b : Symbol(b, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 6, 5))
+>bIndex : Symbol(bIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 7, 5))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 6, 17))
+}
+
+interface Foo {
+>Foo : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 10, 1))
+
+    x: number | undefined;
+>x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 12, 15))
+}
+const c: Foo[] = [];
+>c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 15, 5))
+>Foo : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 10, 1))
+
+const cIndex = 1;
+>cIndex : Symbol(cIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 16, 5))
+
+if (c[cIndex].x) {
+>c[cIndex].x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 12, 15))
+>c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 15, 5))
+>cIndex : Symbol(cIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 16, 5))
+>x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 12, 15))
+
+    c[cIndex].x // number
+>c[cIndex].x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 12, 15))
+>c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 15, 5))
+>cIndex : Symbol(cIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 16, 5))
+>x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty5.ts, 12, 15))
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty5.types

@@ -0,0 +1,84 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty5.ts ===
+const a: { key?: { x?: number } } = {};
+>a : { key?: { x?: number | undefined; } | undefined; }
+>key : { x?: number | undefined; } | undefined
+>x : number | undefined
+>{} : {}
+
+const aIndex = "key";
+>aIndex : "key"
+>"key" : "key"
+
+if (a[aIndex] && a[aIndex].x) {
+>a[aIndex] && a[aIndex].x : number | undefined
+>a[aIndex] : { x?: number | undefined; } | undefined
+>a : { key?: { x?: number | undefined; } | undefined; }
+>aIndex : "key"
+>a[aIndex].x : number | undefined
+>a[aIndex] : { x?: number | undefined; }
+>a : { key?: { x?: number | undefined; } | undefined; }
+>aIndex : "key"
+>x : number | undefined
+
+    a[aIndex].x // number
+>a[aIndex].x : number
+>a[aIndex] : { x?: number | undefined; }
+>a : { key?: { x?: number | undefined; } | undefined; }
+>aIndex : "key"
+>x : number
+}
+
+const b: { key: { x?: number } } = { key: {} };
+>b : { key: {    x?: number;}; }
+>key : { x?: number | undefined; }
+>x : number | undefined
+>{ key: {} } : { key: {}; }
+>key : {}
+>{} : {}
+
+const bIndex = "key";
+>bIndex : "key"
+>"key" : "key"
+
+if (b[bIndex].x) {
+>b[bIndex].x : number | undefined
+>b[bIndex] : { x?: number | undefined; }
+>b : { key: { x?: number | undefined; }; }
+>bIndex : "key"
+>x : number | undefined
+
+    b[bIndex].x // number
+>b[bIndex].x : number
+>b[bIndex] : { x?: number | undefined; }
+>b : { key: { x?: number | undefined; }; }
+>bIndex : "key"
+>x : number
+}
+
+interface Foo {
+    x: number | undefined;
+>x : number | undefined
+}
+const c: Foo[] = [];
+>c : Foo[]
+>[] : never[]
+
+const cIndex = 1;
+>cIndex : 1
+>1 : 1
+
+if (c[cIndex].x) {
+>c[cIndex].x : number | undefined
+>c[cIndex] : Foo
+>c : Foo[]
+>cIndex : 1
+>x : number | undefined
+
+    c[cIndex].x // number
+>c[cIndex].x : number
+>c[cIndex] : Foo
+>c : Foo[]
+>cIndex : 1
+>x : number
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty6.js

@@ -0,0 +1,37 @@
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty6.ts]
+declare const aIndex: "key";
+const a: { key?: { x?: number } } = {};
+if (a[aIndex] && a[aIndex].x) {
+    a[aIndex].x // number
+}
+
+declare const bIndex: "key";
+const b: { key: { x?: number } } = { key: {} };
+if (b[bIndex].x) {
+    b[bIndex].x // number
+}
+
+declare const cIndex: 1;
+interface Foo {
+    x: number | undefined;
+}
+const c: Foo[] = [];
+if (c[cIndex].x) {
+    c[cIndex].x // number
+}
+
+
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty6.js]
+"use strict";
+var a = {};
+if (a[aIndex] && a[aIndex].x) {
+    a[aIndex].x; // number
+}
+var b = { key: {} };
+if (b[bIndex].x) {
+    b[bIndex].x; // number
+}
+var c = [];
+if (c[cIndex].x) {
+    c[cIndex].x; // number
+}

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty6.symbols

@@ -0,0 +1,72 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty6.ts ===
+declare const aIndex: "key";
+>aIndex : Symbol(aIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 0, 13))
+
+const a: { key?: { x?: number } } = {};
+>a : Symbol(a, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 1, 5))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 1, 10))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 1, 18))
+
+if (a[aIndex] && a[aIndex].x) {
+>a : Symbol(a, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 1, 5))
+>aIndex : Symbol(aIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 0, 13))
+>a[aIndex].x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 1, 18))
+>a : Symbol(a, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 1, 5))
+>aIndex : Symbol(aIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 0, 13))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 1, 18))
+
+    a[aIndex].x // number
+>a[aIndex].x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 1, 18))
+>a : Symbol(a, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 1, 5))
+>aIndex : Symbol(aIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 0, 13))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 1, 18))
+}
+
+declare const bIndex: "key";
+>bIndex : Symbol(bIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 6, 13))
+
+const b: { key: { x?: number } } = { key: {} };
+>b : Symbol(b, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 7, 5))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 7, 10))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 7, 17))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 7, 36))
+
+if (b[bIndex].x) {
+>b[bIndex].x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 7, 17))
+>b : Symbol(b, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 7, 5))
+>bIndex : Symbol(bIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 6, 13))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 7, 17))
+
+    b[bIndex].x // number
+>b[bIndex].x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 7, 17))
+>b : Symbol(b, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 7, 5))
+>bIndex : Symbol(bIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 6, 13))
+>x : Symbol(x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 7, 17))
+}
+
+declare const cIndex: 1;
+>cIndex : Symbol(cIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 12, 13))
+
+interface Foo {
+>Foo : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 12, 24))
+
+    x: number | undefined;
+>x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 13, 15))
+}
+const c: Foo[] = [];
+>c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 16, 5))
+>Foo : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 12, 24))
+
+if (c[cIndex].x) {
+>c[cIndex].x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 13, 15))
+>c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 16, 5))
+>cIndex : Symbol(cIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 12, 13))
+>x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 13, 15))
+
+    c[cIndex].x // number
+>c[cIndex].x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 13, 15))
+>c : Symbol(c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 16, 5))
+>cIndex : Symbol(cIndex, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 12, 13))
+>x : Symbol(Foo.x, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty6.ts, 13, 15))
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty6.types

@@ -0,0 +1,81 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty6.ts ===
+declare const aIndex: "key";
+>aIndex : "key"
+
+const a: { key?: { x?: number } } = {};
+>a : { key?: { x?: number | undefined; } | undefined; }
+>key : { x?: number | undefined; } | undefined
+>x : number | undefined
+>{} : {}
+
+if (a[aIndex] && a[aIndex].x) {
+>a[aIndex] && a[aIndex].x : number | undefined
+>a[aIndex] : { x?: number | undefined; } | undefined
+>a : { key?: { x?: number | undefined; } | undefined; }
+>aIndex : "key"
+>a[aIndex].x : number | undefined
+>a[aIndex] : { x?: number | undefined; }
+>a : { key?: { x?: number | undefined; } | undefined; }
+>aIndex : "key"
+>x : number | undefined
+
+    a[aIndex].x // number
+>a[aIndex].x : number
+>a[aIndex] : { x?: number | undefined; }
+>a : { key?: { x?: number | undefined; } | undefined; }
+>aIndex : "key"
+>x : number
+}
+
+declare const bIndex: "key";
+>bIndex : "key"
+
+const b: { key: { x?: number } } = { key: {} };
+>b : { key: {    x?: number;}; }
+>key : { x?: number | undefined; }
+>x : number | undefined
+>{ key: {} } : { key: {}; }
+>key : {}
+>{} : {}
+
+if (b[bIndex].x) {
+>b[bIndex].x : number | undefined
+>b[bIndex] : { x?: number | undefined; }
+>b : { key: { x?: number | undefined; }; }
+>bIndex : "key"
+>x : number | undefined
+
+    b[bIndex].x // number
+>b[bIndex].x : number
+>b[bIndex] : { x?: number | undefined; }
+>b : { key: { x?: number | undefined; }; }
+>bIndex : "key"
+>x : number
+}
+
+declare const cIndex: 1;
+>cIndex : 1
+
+interface Foo {
+    x: number | undefined;
+>x : number | undefined
+}
+const c: Foo[] = [];
+>c : Foo[]
+>[] : never[]
+
+if (c[cIndex].x) {
+>c[cIndex].x : number | undefined
+>c[cIndex] : Foo
+>c : Foo[]
+>cIndex : 1
+>x : number | undefined
+
+    c[cIndex].x // number
+>c[cIndex].x : number
+>c[cIndex] : Foo
+>c : Foo[]
+>cIndex : 1
+>x : number
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty7.js

@@ -0,0 +1,25 @@
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty7.ts]
+export namespace Foo {
+    export const key = Symbol();
+}
+
+export class C {
+    [Foo.key]: string;
+
+    constructor() {
+        this[Foo.key] = "hello";
+    }
+}
+
+
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty7.js]
+export var Foo;
+(function (Foo) {
+    Foo.key = Symbol();
+})(Foo || (Foo = {}));
+export class C {
+    [Foo.key];
+    constructor() {
+        this[Foo.key] = "hello";
+    }
+}

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty7.symbols

@@ -0,0 +1,27 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty7.ts ===
+export namespace Foo {
+>Foo : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty7.ts, 0, 0))
+
+    export const key = Symbol();
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty7.ts, 1, 16))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2019.symbol.d.ts, --, --))
+}
+
+export class C {
+>C : Symbol(C, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty7.ts, 2, 1))
+
+    [Foo.key]: string;
+>[Foo.key] : Symbol(C[Foo.key], Decl(typeGuardNarrowsIndexedAccessOfKnownProperty7.ts, 4, 16))
+>Foo.key : Symbol(Foo.key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty7.ts, 1, 16))
+>Foo : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty7.ts, 0, 0))
+>key : Symbol(Foo.key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty7.ts, 1, 16))
+
+    constructor() {
+        this[Foo.key] = "hello";
+>this : Symbol(C, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty7.ts, 2, 1))
+>Foo.key : Symbol(Foo.key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty7.ts, 1, 16))
+>Foo : Symbol(Foo, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty7.ts, 0, 0))
+>key : Symbol(Foo.key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty7.ts, 1, 16))
+    }
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty7.types

@@ -0,0 +1,31 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty7.ts ===
+export namespace Foo {
+>Foo : typeof Foo
+
+    export const key = Symbol();
+>key : unique symbol
+>Symbol() : unique symbol
+>Symbol : SymbolConstructor
+}
+
+export class C {
+>C : C
+
+    [Foo.key]: string;
+>[Foo.key] : string
+>Foo.key : unique symbol
+>Foo : typeof Foo
+>key : unique symbol
+
+    constructor() {
+        this[Foo.key] = "hello";
+>this[Foo.key] = "hello" : "hello"
+>this[Foo.key] : string
+>this : this
+>Foo.key : unique symbol
+>Foo : typeof Foo
+>key : unique symbol
+>"hello" : "hello"
+    }
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty8.js

@@ -0,0 +1,26 @@
+//// [tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty8.ts] ////
+
+//// [a.ts]
+export const key = "a";
+
+//// [b.ts]
+import * as a from "./a";
+export class C {
+    [a.key]: string;
+
+    constructor() {
+        this[a.key] = "foo";
+    }
+}
+
+
+//// [a.js]
+export const key = "a";
+//// [b.js]
+import * as a from "./a";
+export class C {
+    [a.key];
+    constructor() {
+        this[a.key] = "foo";
+    }
+}

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty8.symbols

@@ -0,0 +1,26 @@
+=== tests/cases/compiler/a.ts ===
+export const key = "a";
+>key : Symbol(key, Decl(a.ts, 0, 12))
+
+=== tests/cases/compiler/b.ts ===
+import * as a from "./a";
+>a : Symbol(a, Decl(b.ts, 0, 6))
+
+export class C {
+>C : Symbol(C, Decl(b.ts, 0, 25))
+
+    [a.key]: string;
+>[a.key] : Symbol(C[a.key], Decl(b.ts, 1, 16))
+>a.key : Symbol(a.key, Decl(a.ts, 0, 12))
+>a : Symbol(a, Decl(b.ts, 0, 6))
+>key : Symbol(a.key, Decl(a.ts, 0, 12))
+
+    constructor() {
+        this[a.key] = "foo";
+>this : Symbol(C, Decl(b.ts, 0, 25))
+>a.key : Symbol(a.key, Decl(a.ts, 0, 12))
+>a : Symbol(a, Decl(b.ts, 0, 6))
+>key : Symbol(a.key, Decl(a.ts, 0, 12))
+    }
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty8.types

@@ -0,0 +1,30 @@
+=== tests/cases/compiler/a.ts ===
+export const key = "a";
+>key : "a"
+>"a" : "a"
+
+=== tests/cases/compiler/b.ts ===
+import * as a from "./a";
+>a : typeof a
+
+export class C {
+>C : C
+
+    [a.key]: string;
+>[a.key] : string
+>a.key : "a"
+>a : typeof a
+>key : "a"
+
+    constructor() {
+        this[a.key] = "foo";
+>this[a.key] = "foo" : "foo"
+>this[a.key] : string
+>this : this
+>a.key : "a"
+>a : typeof a
+>key : "a"
+>"foo" : "foo"
+    }
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty9.errors.txt

@@ -0,0 +1,21 @@
+tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty9.ts(5,13): error TS6133: 'c' is declared but its value is never read.
+tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty9.ts(6,13): error TS6133: 'd' is declared but its value is never read.
+
+
+==== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty9.ts (2 errors) ====
+    class C1 {
+        private a = "a"; // ok
+        private b = "b"; // ok
+    
+        private c = "c"; // error unused prop
+                ~
+!!! error TS6133: 'c' is declared but its value is never read.
+        private d = "d"; // error unused prop
+                ~
+!!! error TS6133: 'd' is declared but its value is never read.
+    
+        getValue(key: "a" | "b") {
+            return this[key];
+        }
+    }
+    

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty9.js

@@ -0,0 +1,25 @@
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty9.ts]
+class C1 {
+    private a = "a"; // ok
+    private b = "b"; // ok
+
+    private c = "c"; // error unused prop
+    private d = "d"; // error unused prop
+
+    getValue(key: "a" | "b") {
+        return this[key];
+    }
+}
+
+
+//// [typeGuardNarrowsIndexedAccessOfKnownProperty9.js]
+"use strict";
+class C1 {
+    a = "a"; // ok
+    b = "b"; // ok
+    c = "c"; // error unused prop
+    d = "d"; // error unused prop
+    getValue(key) {
+        return this[key];
+    }
+}

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty9.symbols

@@ -0,0 +1,26 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty9.ts ===
+class C1 {
+>C1 : Symbol(C1, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty9.ts, 0, 0))
+
+    private a = "a"; // ok
+>a : Symbol(C1.a, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty9.ts, 0, 10))
+
+    private b = "b"; // ok
+>b : Symbol(C1.b, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty9.ts, 1, 20))
+
+    private c = "c"; // error unused prop
+>c : Symbol(C1.c, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty9.ts, 2, 20))
+
+    private d = "d"; // error unused prop
+>d : Symbol(C1.d, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty9.ts, 4, 20))
+
+    getValue(key: "a" | "b") {
+>getValue : Symbol(C1.getValue, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty9.ts, 5, 20))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty9.ts, 7, 13))
+
+        return this[key];
+>this : Symbol(C1, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty9.ts, 0, 0))
+>key : Symbol(key, Decl(typeGuardNarrowsIndexedAccessOfKnownProperty9.ts, 7, 13))
+    }
+}
+

tests/baselines/reference/typeGuardNarrowsIndexedAccessOfKnownProperty9.types

@@ -0,0 +1,31 @@
+=== tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty9.ts ===
+class C1 {
+>C1 : C1
+
+    private a = "a"; // ok
+>a : string
+>"a" : "a"
+
+    private b = "b"; // ok
+>b : string
+>"b" : "b"
+
+    private c = "c"; // error unused prop
+>c : string
+>"c" : "c"
+
+    private d = "d"; // error unused prop
+>d : string
+>"d" : "d"
+
+    getValue(key: "a" | "b") {
+>getValue : (key: "a" | "b") => string
+>key : "a" | "b"
+
+        return this[key];
+>this[key] : string
+>this : this
+>key : "a" | "b"
+    }
+}
+

tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty2.ts

@@ -0,0 +1,9 @@
+// @strict: true
+
+const foo: { key?: number } = {};
+const key = 'key' as const;
+
+if (foo[key]) {
+    foo[key]; // number
+    foo.key;  // number
+}

tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty3.ts

@@ -0,0 +1,10 @@
+// @strict: true
+
+type Foo = (number | undefined)[] | undefined;
+
+const foo: Foo = [1, 2, 3];
+const index = 1;
+
+if (foo !== undefined && foo[index] !== undefined && foo[index] >= 0) {
+    foo[index] // number
+}

tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty4.ts

@@ -0,0 +1,15 @@
+// @strict: true
+
+class Foo {
+    x: number | undefined;
+
+    constructor() {
+        this.x = 5;
+
+        this.x;    // number
+        this['x']; // number
+
+        const key = 'x';
+        this[key]; // number
+    }
+}

tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty5.ts

@@ -0,0 +1,22 @@
+// @strict: true
+
+const a: { key?: { x?: number } } = {};
+const aIndex = "key";
+if (a[aIndex] && a[aIndex].x) {
+    a[aIndex].x // number
+}
+
+const b: { key: { x?: number } } = { key: {} };
+const bIndex = "key";
+if (b[bIndex].x) {
+    b[bIndex].x // number
+}
+
+interface Foo {
+    x: number | undefined;
+}
+const c: Foo[] = [];
+const cIndex = 1;
+if (c[cIndex].x) {
+    c[cIndex].x // number
+}

tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty6.ts

@@ -0,0 +1,22 @@
+// @strict: true
+
+declare const aIndex: "key";
+const a: { key?: { x?: number } } = {};
+if (a[aIndex] && a[aIndex].x) {
+    a[aIndex].x // number
+}
+
+declare const bIndex: "key";
+const b: { key: { x?: number } } = { key: {} };
+if (b[bIndex].x) {
+    b[bIndex].x // number
+}
+
+declare const cIndex: 1;
+interface Foo {
+    x: number | undefined;
+}
+const c: Foo[] = [];
+if (c[cIndex].x) {
+    c[cIndex].x // number
+}

tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty7.ts

@@ -0,0 +1,14 @@
+// @strict: true
+// @target: esnext
+
+export namespace Foo {
+    export const key = Symbol();
+}
+
+export class C {
+    [Foo.key]: string;
+
+    constructor() {
+        this[Foo.key] = "hello";
+    }
+}

tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty8.ts

@@ -0,0 +1,15 @@
+// @strict: true
+// @target: esnext
+
+// @filename: ./a.ts
+export const key = "a";
+
+// @filename: ./b.ts
+import * as a from "./a";
+export class C {
+    [a.key]: string;
+
+    constructor() {
+        this[a.key] = "foo";
+    }
+}

tests/cases/compiler/typeGuardNarrowsIndexedAccessOfKnownProperty9.ts

@@ -0,0 +1,15 @@
+// @noUnusedLocals: true
+// @strict: true
+// @target: esnext
+
+class C1 {
+    private a = "a"; // ok
+    private b = "b"; // ok
+
+    private c = "c"; // error unused prop
+    private d = "d"; // error unused prop
+
+    getValue(key: "a" | "b") {
+        return this[key];
+    }
+}

tests/cases/conformance/classes/propertyMemberDeclarations/strictPropertyInitialization.ts

@@ -1,5 +1,5 @@
 // @strict: true
-// @target:es2015
+// @target: es2015
 // @declaration: true
 
 // Properties with non-undefined types require initialization
@@ -135,3 +135,18 @@ class C11 {
         this.#b = someValue();
     }
 }
+
+const a = 'a';
+const b = Symbol();
+
+class C12 {
+    [a]: number;
+    [b]: number;
+    ['c']: number;
+
+    constructor() {
+        this[a] = 1;
+        this[b] = 1;
+        this['c'] = 1;
+    }
+}