Report error only on local declaration with additional related information (#49746)

* Add test where the errors are reported in different file
Test for #49739

* Report error only on local declaration with additional related information
Fixes #49739

* Handle existing tests

src/compiler/checker.ts

@@ -39552,8 +39552,9 @@ namespace ts {
             }
             const indexInfos = getApplicableIndexInfos(type, propNameType);
             const interfaceDeclaration = getObjectFlags(type) & ObjectFlags.Interface ? getDeclarationOfKind(type.symbol, SyntaxKind.InterfaceDeclaration) : undefined;
-            const localPropDeclaration = declaration && declaration.kind === SyntaxKind.BinaryExpression ||
-                name && name.kind === SyntaxKind.ComputedPropertyName || getParentOfSymbol(prop) === type.symbol ? declaration : undefined;
+            const propDeclaration = declaration && declaration.kind === SyntaxKind.BinaryExpression ||
+                name && name.kind === SyntaxKind.ComputedPropertyName ? declaration : undefined;
+            const localPropDeclaration = getParentOfSymbol(prop) === type.symbol ? declaration : undefined;
             for (const info of indexInfos) {
                 const localIndexDeclaration = info.declaration && getParentOfSymbol(getSymbolOfNode(info.declaration)) === type.symbol ? info.declaration : undefined;
                 // We check only when (a) the property is declared in the containing type, or (b) the applicable index signature is declared
@@ -39562,8 +39563,12 @@ namespace ts {
                 const errorNode = localPropDeclaration || localIndexDeclaration ||
                     (interfaceDeclaration && !some(getBaseTypes(type as InterfaceType), base => !!getPropertyOfObjectType(base, prop.escapedName) && !!getIndexTypeOfType(base, info.keyType)) ? interfaceDeclaration : undefined);
                 if (errorNode && !isTypeAssignableTo(propType, info.type)) {
-                    error(errorNode, Diagnostics.Property_0_of_type_1_is_not_assignable_to_2_index_type_3,
+                    const diagnostic = createError(errorNode, Diagnostics.Property_0_of_type_1_is_not_assignable_to_2_index_type_3,
                         symbolToString(prop), typeToString(propType), typeToString(info.keyType), typeToString(info.type));
+                    if (propDeclaration && errorNode !== propDeclaration) {
+                        addRelatedInfo(diagnostic, createDiagnosticForNode(propDeclaration, Diagnostics._0_is_declared_here, symbolToString(prop)));
+                    }
+                    diagnostics.add(diagnostic);
                 }
             }
         }

tests/baselines/reference/computedPropertyNames45_ES5.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/conformance/es6/computedProperties/computedPropertyNames45_ES5.ts(5,9): error TS2411: Property '["get1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.
+tests/cases/conformance/es6/computedProperties/computedPropertyNames45_ES5.ts(10,5): error TS2411: Property '["get1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.
 tests/cases/conformance/es6/computedProperties/computedPropertyNames45_ES5.ts(11,9): error TS2411: Property '["set1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.
 
 
@@ -8,13 +8,14 @@ tests/cases/conformance/es6/computedProperties/computedPropertyNames45_ES5.ts(11
     
     class C {
         get ["get1"]() { return new Foo }
-            ~~~~~~~~
-!!! error TS2411: Property '["get1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.
     }
     
     class D extends C {
         // No error when the indexer is in a class more derived than the computed property
         [s: string]: Foo2;
+        ~~~~~~~~~~~~~~~~~~
+!!! error TS2411: Property '["get1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.
+!!! related TS2728 tests/cases/conformance/es6/computedProperties/computedPropertyNames45_ES5.ts:5:9: '["get1"]' is declared here.
         set ["set1"](p: Foo) { }
             ~~~~~~~~
 !!! error TS2411: Property '["set1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.

tests/baselines/reference/computedPropertyNames45_ES6.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/conformance/es6/computedProperties/computedPropertyNames45_ES6.ts(5,9): error TS2411: Property '["get1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.
+tests/cases/conformance/es6/computedProperties/computedPropertyNames45_ES6.ts(10,5): error TS2411: Property '["get1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.
 tests/cases/conformance/es6/computedProperties/computedPropertyNames45_ES6.ts(11,9): error TS2411: Property '["set1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.
 
 
@@ -8,13 +8,14 @@ tests/cases/conformance/es6/computedProperties/computedPropertyNames45_ES6.ts(11
     
     class C {
         get ["get1"]() { return new Foo }
-            ~~~~~~~~
-!!! error TS2411: Property '["get1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.
     }
     
     class D extends C {
         // No error when the indexer is in a class more derived than the computed property
         [s: string]: Foo2;
+        ~~~~~~~~~~~~~~~~~~
+!!! error TS2411: Property '["get1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.
+!!! related TS2728 tests/cases/conformance/es6/computedProperties/computedPropertyNames45_ES6.ts:5:9: '["get1"]' is declared here.
         set ["set1"](p: Foo) { }
             ~~~~~~~~
 !!! error TS2411: Property '["set1"]' of type 'Foo' is not assignable to 'string' index type 'Foo2'.

tests/baselines/reference/indexSignatureInOtherFile.errors.txt

@@ -0,0 +1,49 @@
+tests/cases/compiler/index.ts(2,3): error TS2411: Property '[Symbol.iterator]' of type '() => IterableIterator<any>' is not assignable to 'symbol' index type 'string'.
+tests/cases/compiler/index.ts(2,3): error TS2411: Property '[Symbol.unscopables]' of type '() => { copyWithin: boolean; entries: boolean; fill: boolean; find: boolean; findIndex: boolean; keys: boolean; values: boolean; }' is not assignable to 'symbol' index type 'string'.
+
+
+==== tests/cases/compiler/index.ts (2 errors) ====
+    class Test extends Array1 {
+      [key: symbol]: string
+      ~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2411: Property '[Symbol.iterator]' of type '() => IterableIterator<any>' is not assignable to 'symbol' index type 'string'.
+!!! related TS2728 tests/cases/compiler/other.ts:14:3: '[Symbol.iterator]' is declared here.
+      ~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2411: Property '[Symbol.unscopables]' of type '() => { copyWithin: boolean; entries: boolean; fill: boolean; find: boolean; findIndex: boolean; keys: boolean; values: boolean; }' is not assignable to 'symbol' index type 'string'.
+!!! related TS2728 tests/cases/compiler/other.ts:23:3: '[Symbol.unscopables]' is declared here.
+    }
+    
+==== tests/cases/compiler/other.ts (0 errors) ====
+    interface Array1<T> {
+      length: number;
+      [n: number]: T;
+    }
+    
+    interface ArrayConstructor1 {
+      new(arrayLength?: number): Array1<any>;
+    }
+    
+    declare var Array1: ArrayConstructor1;
+    
+    // iterable.d.ts
+    interface Array1<T> {
+      [Symbol.iterator](): IterableIterator<T>;
+    }
+    
+    // symbol.wellknown.d.ts
+    interface Array1<T> {
+      /**
+       * Returns an object whose properties have the value 'true'
+       * when they will be absent when used in a 'with' statement.
+       */
+      [Symbol.unscopables](): {
+          copyWithin: boolean;
+          entries: boolean;
+          fill: boolean;
+          find: boolean;
+          findIndex: boolean;
+          keys: boolean;
+          values: boolean;
+      };
+    }
+    

tests/baselines/reference/indexSignatureInOtherFile.js

@@ -0,0 +1,46 @@
+//// [tests/cases/compiler/indexSignatureInOtherFile.ts] ////
+
+//// [index.ts]
+class Test extends Array1 {
+  [key: symbol]: string
+}
+
+//// [other.ts]
+interface Array1<T> {
+  length: number;
+  [n: number]: T;
+}
+
+interface ArrayConstructor1 {
+  new(arrayLength?: number): Array1<any>;
+}
+
+declare var Array1: ArrayConstructor1;
+
+// iterable.d.ts
+interface Array1<T> {
+  [Symbol.iterator](): IterableIterator<T>;
+}
+
+// symbol.wellknown.d.ts
+interface Array1<T> {
+  /**
+   * Returns an object whose properties have the value 'true'
+   * when they will be absent when used in a 'with' statement.
+   */
+  [Symbol.unscopables](): {
+      copyWithin: boolean;
+      entries: boolean;
+      fill: boolean;
+      find: boolean;
+      findIndex: boolean;
+      keys: boolean;
+      values: boolean;
+  };
+}
+
+
+//// [index.js]
+class Test extends Array1 {
+}
+//// [other.js]

tests/baselines/reference/indexSignatureInOtherFile.symbols

@@ -0,0 +1,87 @@
+=== tests/cases/compiler/index.ts ===
+class Test extends Array1 {
+>Test : Symbol(Test, Decl(index.ts, 0, 0))
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+
+  [key: symbol]: string
+>key : Symbol(key, Decl(index.ts, 1, 3))
+}
+
+=== tests/cases/compiler/other.ts ===
+interface Array1<T> {
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+>T : Symbol(T, Decl(other.ts, 0, 17), Decl(other.ts, 12, 17), Decl(other.ts, 17, 17))
+
+  length: number;
+>length : Symbol(Array1.length, Decl(other.ts, 0, 21))
+
+  [n: number]: T;
+>n : Symbol(n, Decl(other.ts, 2, 3))
+>T : Symbol(T, Decl(other.ts, 0, 17), Decl(other.ts, 12, 17), Decl(other.ts, 17, 17))
+}
+
+interface ArrayConstructor1 {
+>ArrayConstructor1 : Symbol(ArrayConstructor1, Decl(other.ts, 3, 1))
+
+  new(arrayLength?: number): Array1<any>;
+>arrayLength : Symbol(arrayLength, Decl(other.ts, 6, 6))
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+}
+
+declare var Array1: ArrayConstructor1;
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+>ArrayConstructor1 : Symbol(ArrayConstructor1, Decl(other.ts, 3, 1))
+
+// iterable.d.ts
+interface Array1<T> {
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+>T : Symbol(T, Decl(other.ts, 0, 17), Decl(other.ts, 12, 17), Decl(other.ts, 17, 17))
+
+  [Symbol.iterator](): IterableIterator<T>;
+>[Symbol.iterator] : Symbol(Array1[Symbol.iterator], Decl(other.ts, 12, 21))
+>Symbol.iterator : Symbol(SymbolConstructor.iterator, Decl(lib.es2015.iterable.d.ts, --, --))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>iterator : Symbol(SymbolConstructor.iterator, Decl(lib.es2015.iterable.d.ts, --, --))
+>IterableIterator : Symbol(IterableIterator, Decl(lib.es2015.iterable.d.ts, --, --))
+>T : Symbol(T, Decl(other.ts, 0, 17), Decl(other.ts, 12, 17), Decl(other.ts, 17, 17))
+}
+
+// symbol.wellknown.d.ts
+interface Array1<T> {
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+>T : Symbol(T, Decl(other.ts, 0, 17), Decl(other.ts, 12, 17), Decl(other.ts, 17, 17))
+
+  /**
+   * Returns an object whose properties have the value 'true'
+   * when they will be absent when used in a 'with' statement.
+   */
+  [Symbol.unscopables](): {
+>[Symbol.unscopables] : Symbol(Array1[Symbol.unscopables], Decl(other.ts, 17, 21))
+>Symbol.unscopables : Symbol(SymbolConstructor.unscopables, Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>unscopables : Symbol(SymbolConstructor.unscopables, Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+
+      copyWithin: boolean;
+>copyWithin : Symbol(copyWithin, Decl(other.ts, 22, 27))
+
+      entries: boolean;
+>entries : Symbol(entries, Decl(other.ts, 23, 26))
+
+      fill: boolean;
+>fill : Symbol(fill, Decl(other.ts, 24, 23))
+
+      find: boolean;
+>find : Symbol(find, Decl(other.ts, 25, 20))
+
+      findIndex: boolean;
+>findIndex : Symbol(findIndex, Decl(other.ts, 26, 20))
+
+      keys: boolean;
+>keys : Symbol(keys, Decl(other.ts, 27, 25))
+
+      values: boolean;
+>values : Symbol(values, Decl(other.ts, 28, 20))
+
+  };
+}
+

tests/baselines/reference/indexSignatureInOtherFile.types

@@ -0,0 +1,71 @@
+=== tests/cases/compiler/index.ts ===
+class Test extends Array1 {
+>Test : Test
+>Array1 : Array1<any>
+
+  [key: symbol]: string
+>key : symbol
+}
+
+=== tests/cases/compiler/other.ts ===
+interface Array1<T> {
+  length: number;
+>length : number
+
+  [n: number]: T;
+>n : number
+}
+
+interface ArrayConstructor1 {
+  new(arrayLength?: number): Array1<any>;
+>arrayLength : number
+}
+
+declare var Array1: ArrayConstructor1;
+>Array1 : ArrayConstructor1
+
+// iterable.d.ts
+interface Array1<T> {
+  [Symbol.iterator](): IterableIterator<T>;
+>[Symbol.iterator] : () => IterableIterator<T>
+>Symbol.iterator : unique symbol
+>Symbol : SymbolConstructor
+>iterator : unique symbol
+}
+
+// symbol.wellknown.d.ts
+interface Array1<T> {
+  /**
+   * Returns an object whose properties have the value 'true'
+   * when they will be absent when used in a 'with' statement.
+   */
+  [Symbol.unscopables](): {
+>[Symbol.unscopables] : () => {    copyWithin: boolean;    entries: boolean;    fill: boolean;    find: boolean;    findIndex: boolean;    keys: boolean;    values: boolean;}
+>Symbol.unscopables : unique symbol
+>Symbol : SymbolConstructor
+>unscopables : unique symbol
+
+      copyWithin: boolean;
+>copyWithin : boolean
+
+      entries: boolean;
+>entries : boolean
+
+      fill: boolean;
+>fill : boolean
+
+      find: boolean;
+>find : boolean
+
+      findIndex: boolean;
+>findIndex : boolean
+
+      keys: boolean;
+>keys : boolean
+
+      values: boolean;
+>values : boolean
+
+  };
+}
+

tests/baselines/reference/indexSignatureInOtherFile1.errors.txt

@@ -0,0 +1,48 @@
+tests/cases/compiler/index.ts(2,3): error TS2411: Property '[Symbol.iterator]' of type '() => IterableIterator<any>' is not assignable to 'symbol' index type 'string'.
+tests/cases/compiler/index.ts(2,3): error TS2411: Property '[Symbol.unscopables]' of type '() => { copyWithin: boolean; entries: boolean; fill: boolean; find: boolean; findIndex: boolean; keys: boolean; values: boolean; }' is not assignable to 'symbol' index type 'string'.
+
+
+==== tests/cases/compiler/other.ts (0 errors) ====
+    interface Array1<T> {
+      length: number;
+      [n: number]: T;
+    }
+    
+    interface ArrayConstructor1 {
+      new(arrayLength?: number): Array1<any>;
+    }
+    
+    declare var Array1: ArrayConstructor1;
+    
+    // iterable.d.ts
+    interface Array1<T> {
+      [Symbol.iterator](): IterableIterator<T>;
+    }
+    
+    // symbol.wellknown.d.ts
+    interface Array1<T> {
+      /**
+       * Returns an object whose properties have the value 'true'
+       * when they will be absent when used in a 'with' statement.
+       */
+      [Symbol.unscopables](): {
+          copyWithin: boolean;
+          entries: boolean;
+          fill: boolean;
+          find: boolean;
+          findIndex: boolean;
+          keys: boolean;
+          values: boolean;
+      };
+    }
+    
+==== tests/cases/compiler/index.ts (2 errors) ====
+    class Test extends Array1 {
+      [key: symbol]: string
+      ~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2411: Property '[Symbol.iterator]' of type '() => IterableIterator<any>' is not assignable to 'symbol' index type 'string'.
+!!! related TS2728 tests/cases/compiler/other.ts:14:3: '[Symbol.iterator]' is declared here.
+      ~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2411: Property '[Symbol.unscopables]' of type '() => { copyWithin: boolean; entries: boolean; fill: boolean; find: boolean; findIndex: boolean; keys: boolean; values: boolean; }' is not assignable to 'symbol' index type 'string'.
+!!! related TS2728 tests/cases/compiler/other.ts:23:3: '[Symbol.unscopables]' is declared here.
+    }

tests/baselines/reference/indexSignatureInOtherFile1.js

@@ -0,0 +1,45 @@
+//// [tests/cases/compiler/indexSignatureInOtherFile1.ts] ////
+
+//// [other.ts]
+interface Array1<T> {
+  length: number;
+  [n: number]: T;
+}
+
+interface ArrayConstructor1 {
+  new(arrayLength?: number): Array1<any>;
+}
+
+declare var Array1: ArrayConstructor1;
+
+// iterable.d.ts
+interface Array1<T> {
+  [Symbol.iterator](): IterableIterator<T>;
+}
+
+// symbol.wellknown.d.ts
+interface Array1<T> {
+  /**
+   * Returns an object whose properties have the value 'true'
+   * when they will be absent when used in a 'with' statement.
+   */
+  [Symbol.unscopables](): {
+      copyWithin: boolean;
+      entries: boolean;
+      fill: boolean;
+      find: boolean;
+      findIndex: boolean;
+      keys: boolean;
+      values: boolean;
+  };
+}
+
+//// [index.ts]
+class Test extends Array1 {
+  [key: symbol]: string
+}
+
+//// [other.js]
+//// [index.js]
+class Test extends Array1 {
+}

tests/baselines/reference/indexSignatureInOtherFile1.symbols

@@ -0,0 +1,86 @@
+=== tests/cases/compiler/other.ts ===
+interface Array1<T> {
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+>T : Symbol(T, Decl(other.ts, 0, 17), Decl(other.ts, 12, 17), Decl(other.ts, 17, 17))
+
+  length: number;
+>length : Symbol(Array1.length, Decl(other.ts, 0, 21))
+
+  [n: number]: T;
+>n : Symbol(n, Decl(other.ts, 2, 3))
+>T : Symbol(T, Decl(other.ts, 0, 17), Decl(other.ts, 12, 17), Decl(other.ts, 17, 17))
+}
+
+interface ArrayConstructor1 {
+>ArrayConstructor1 : Symbol(ArrayConstructor1, Decl(other.ts, 3, 1))
+
+  new(arrayLength?: number): Array1<any>;
+>arrayLength : Symbol(arrayLength, Decl(other.ts, 6, 6))
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+}
+
+declare var Array1: ArrayConstructor1;
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+>ArrayConstructor1 : Symbol(ArrayConstructor1, Decl(other.ts, 3, 1))
+
+// iterable.d.ts
+interface Array1<T> {
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+>T : Symbol(T, Decl(other.ts, 0, 17), Decl(other.ts, 12, 17), Decl(other.ts, 17, 17))
+
+  [Symbol.iterator](): IterableIterator<T>;
+>[Symbol.iterator] : Symbol(Array1[Symbol.iterator], Decl(other.ts, 12, 21))
+>Symbol.iterator : Symbol(SymbolConstructor.iterator, Decl(lib.es2015.iterable.d.ts, --, --))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>iterator : Symbol(SymbolConstructor.iterator, Decl(lib.es2015.iterable.d.ts, --, --))
+>IterableIterator : Symbol(IterableIterator, Decl(lib.es2015.iterable.d.ts, --, --))
+>T : Symbol(T, Decl(other.ts, 0, 17), Decl(other.ts, 12, 17), Decl(other.ts, 17, 17))
+}
+
+// symbol.wellknown.d.ts
+interface Array1<T> {
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+>T : Symbol(T, Decl(other.ts, 0, 17), Decl(other.ts, 12, 17), Decl(other.ts, 17, 17))
+
+  /**
+   * Returns an object whose properties have the value 'true'
+   * when they will be absent when used in a 'with' statement.
+   */
+  [Symbol.unscopables](): {
+>[Symbol.unscopables] : Symbol(Array1[Symbol.unscopables], Decl(other.ts, 17, 21))
+>Symbol.unscopables : Symbol(SymbolConstructor.unscopables, Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>unscopables : Symbol(SymbolConstructor.unscopables, Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+
+      copyWithin: boolean;
+>copyWithin : Symbol(copyWithin, Decl(other.ts, 22, 27))
+
+      entries: boolean;
+>entries : Symbol(entries, Decl(other.ts, 23, 26))
+
+      fill: boolean;
+>fill : Symbol(fill, Decl(other.ts, 24, 23))
+
+      find: boolean;
+>find : Symbol(find, Decl(other.ts, 25, 20))
+
+      findIndex: boolean;
+>findIndex : Symbol(findIndex, Decl(other.ts, 26, 20))
+
+      keys: boolean;
+>keys : Symbol(keys, Decl(other.ts, 27, 25))
+
+      values: boolean;
+>values : Symbol(values, Decl(other.ts, 28, 20))
+
+  };
+}
+
+=== tests/cases/compiler/index.ts ===
+class Test extends Array1 {
+>Test : Symbol(Test, Decl(index.ts, 0, 0))
+>Array1 : Symbol(Array1, Decl(other.ts, 0, 0), Decl(other.ts, 9, 11), Decl(other.ts, 9, 38), Decl(other.ts, 14, 1))
+
+  [key: symbol]: string
+>key : Symbol(key, Decl(index.ts, 1, 3))
+}

tests/baselines/reference/indexSignatureInOtherFile1.types

@@ -0,0 +1,70 @@
+=== tests/cases/compiler/other.ts ===
+interface Array1<T> {
+  length: number;
+>length : number
+
+  [n: number]: T;
+>n : number
+}
+
+interface ArrayConstructor1 {
+  new(arrayLength?: number): Array1<any>;
+>arrayLength : number
+}
+
+declare var Array1: ArrayConstructor1;
+>Array1 : ArrayConstructor1
+
+// iterable.d.ts
+interface Array1<T> {
+  [Symbol.iterator](): IterableIterator<T>;
+>[Symbol.iterator] : () => IterableIterator<T>
+>Symbol.iterator : unique symbol
+>Symbol : SymbolConstructor
+>iterator : unique symbol
+}
+
+// symbol.wellknown.d.ts
+interface Array1<T> {
+  /**
+   * Returns an object whose properties have the value 'true'
+   * when they will be absent when used in a 'with' statement.
+   */
+  [Symbol.unscopables](): {
+>[Symbol.unscopables] : () => {    copyWithin: boolean;    entries: boolean;    fill: boolean;    find: boolean;    findIndex: boolean;    keys: boolean;    values: boolean;}
+>Symbol.unscopables : unique symbol
+>Symbol : SymbolConstructor
+>unscopables : unique symbol
+
+      copyWithin: boolean;
+>copyWithin : boolean
+
+      entries: boolean;
+>entries : boolean
+
+      fill: boolean;
+>fill : boolean
+
+      find: boolean;
+>find : boolean
+
+      findIndex: boolean;
+>findIndex : boolean
+
+      keys: boolean;
+>keys : boolean
+
+      values: boolean;
+>values : boolean
+
+  };
+}
+
+=== tests/cases/compiler/index.ts ===
+class Test extends Array1 {
+>Test : Test
+>Array1 : Array1<any>
+
+  [key: symbol]: string
+>key : symbol
+}

tests/baselines/reference/symbolProperty32.errors.txt

@@ -1,14 +1,15 @@
-tests/cases/conformance/es6/Symbols/symbolProperty32.ts(2,5): error TS2411: Property '[Symbol.toStringTag]' of type '() => { x: string; }' is not assignable to 'symbol' index type '() => { x: number; }'.
+tests/cases/conformance/es6/Symbols/symbolProperty32.ts(7,5): error TS2411: Property '[Symbol.toStringTag]' of type '() => { x: string; }' is not assignable to 'symbol' index type '() => { x: number; }'.
 
 
 ==== tests/cases/conformance/es6/Symbols/symbolProperty32.ts (1 errors) ====
     class C1 {
         [Symbol.toStringTag]() {
-        ~~~~~~~~~~~~~~~~~~~~
-!!! error TS2411: Property '[Symbol.toStringTag]' of type '() => { x: string; }' is not assignable to 'symbol' index type '() => { x: number; }'.
             return { x: "" };
         }
     }
     class C2 extends C1 {
         [s: symbol]: () => { x: number };
+        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2411: Property '[Symbol.toStringTag]' of type '() => { x: string; }' is not assignable to 'symbol' index type '() => { x: number; }'.
+!!! related TS2728 tests/cases/conformance/es6/Symbols/symbolProperty32.ts:2:5: '[Symbol.toStringTag]' is declared here.
     }

tests/cases/compiler/indexSignatureInOtherFile.ts

@@ -0,0 +1,39 @@
+// @target: es2015
+// @Filename: index.ts
+class Test extends Array1 {
+  [key: symbol]: string
+}
+
+// @Filename: other.ts
+interface Array1<T> {
+  length: number;
+  [n: number]: T;
+}
+
+interface ArrayConstructor1 {
+  new(arrayLength?: number): Array1<any>;
+}
+
+declare var Array1: ArrayConstructor1;
+
+// iterable.d.ts
+interface Array1<T> {
+  [Symbol.iterator](): IterableIterator<T>;
+}
+
+// symbol.wellknown.d.ts
+interface Array1<T> {
+  /**
+   * Returns an object whose properties have the value 'true'
+   * when they will be absent when used in a 'with' statement.
+   */
+  [Symbol.unscopables](): {
+      copyWithin: boolean;
+      entries: boolean;
+      fill: boolean;
+      find: boolean;
+      findIndex: boolean;
+      keys: boolean;
+      values: boolean;
+  };
+}

tests/cases/compiler/indexSignatureInOtherFile1.ts

@@ -0,0 +1,39 @@
+// @target: es2015
+// @Filename: other.ts
+interface Array1<T> {
+  length: number;
+  [n: number]: T;
+}
+
+interface ArrayConstructor1 {
+  new(arrayLength?: number): Array1<any>;
+}
+
+declare var Array1: ArrayConstructor1;
+
+// iterable.d.ts
+interface Array1<T> {
+  [Symbol.iterator](): IterableIterator<T>;
+}
+
+// symbol.wellknown.d.ts
+interface Array1<T> {
+  /**
+   * Returns an object whose properties have the value 'true'
+   * when they will be absent when used in a 'with' statement.
+   */
+  [Symbol.unscopables](): {
+      copyWithin: boolean;
+      entries: boolean;
+      fill: boolean;
+      find: boolean;
+      findIndex: boolean;
+      keys: boolean;
+      values: boolean;
+  };
+}
+
+// @Filename: index.ts
+class Test extends Array1 {
+  [key: symbol]: string
+}