Change 'keyof T' to always be string-like

src/compiler/checker.ts

@@ -142,7 +142,6 @@ namespace ts {
         const voidType = createIntrinsicType(TypeFlags.Void, "void");
         const neverType = createIntrinsicType(TypeFlags.Never, "never");
         const silentNeverType = createIntrinsicType(TypeFlags.Never, "never");
-        const stringOrNumberType = getUnionType([stringType, numberType]);
 
         const emptyObjectType = createAnonymousType(undefined, emptySymbols, emptyArray, emptyArray, undefined, undefined);
 
@@ -3217,9 +3216,11 @@ namespace ts {
                 }
             }
 
-            // A variable declared in a for..in statement is always of type string
+            // A variable declared in a for..in statement is of type string, or of type keyof T when the
+            // right hand expression is of a type parameter type.
             if (declaration.parent.parent.kind === SyntaxKind.ForInStatement) {
-                return stringType;
+                const indexType = getIndexType(checkNonNullExpression((<ForInStatement>declaration.parent.parent).expression));
+                return indexType.flags & TypeFlags.Index ? indexType : stringType;
             }
 
             if (declaration.parent.parent.kind === SyntaxKind.ForOfStatement) {
@@ -4688,7 +4689,6 @@ namespace ts {
                 t.flags & TypeFlags.NumberLike ? globalNumberType :
                 t.flags & TypeFlags.BooleanLike ? globalBooleanType :
                 t.flags & TypeFlags.ESSymbol ? getGlobalESSymbolType() :
-                t.flags & TypeFlags.Index ? stringOrNumberType :
                 t;
         }
 
@@ -5920,8 +5920,7 @@ namespace ts {
         function getIndexType(type: Type): Type {
             return type.flags & TypeFlags.TypeParameter ? getIndexTypeForTypeParameter(<TypeParameter>type) :
                 getObjectFlags(type) & ObjectFlags.Mapped ? getConstraintTypeFromMappedType(<MappedType>type) :
-                type.flags & TypeFlags.Any || getIndexInfoOfType(type, IndexKind.String) ? stringOrNumberType :
-                getIndexInfoOfType(type, IndexKind.Number) ? getUnionType([numberType, getLiteralTypeFromPropertyNames(type)]) :
+                type.flags & TypeFlags.Any || getIndexInfoOfType(type, IndexKind.String) ? stringType :
                 getLiteralTypeFromPropertyNames(type);
         }
 
@@ -6040,10 +6039,9 @@ namespace ts {
                 return indexedAccessTypes[id] || (indexedAccessTypes[id] = createIndexedAccessType(objectType, indexType));
             }
             const apparentObjectType = getApparentType(objectType);
-            const apparentIndexType = indexType.flags & TypeFlags.Index ? stringOrNumberType : indexType;
-            if (apparentIndexType.flags & TypeFlags.Union && !(apparentIndexType.flags & TypeFlags.Primitive)) {
+            if (indexType.flags & TypeFlags.Union && !(indexType.flags & TypeFlags.Primitive)) {
                 const propTypes: Type[] = [];
-                for (const t of (<UnionType>apparentIndexType).types) {
+                for (const t of (<UnionType>indexType).types) {
                     const propType = getPropertyTypeForIndexType(apparentObjectType, t, accessNode, /*cacheSymbol*/ false);
                     if (propType === unknownType) {
                         return unknownType;
@@ -6052,7 +6050,7 @@ namespace ts {
                 }
                 return getUnionType(propTypes);
             }
-            return getPropertyTypeForIndexType(apparentObjectType, apparentIndexType, accessNode, /*cacheSymbol*/ true);
+            return getPropertyTypeForIndexType(apparentObjectType, indexType, accessNode, /*cacheSymbol*/ true);
         }
 
         function getTypeFromIndexedAccessTypeNode(node: IndexedAccessTypeNode) {
@@ -7124,16 +7122,6 @@ namespace ts {
 
                 if (isSimpleTypeRelatedTo(source, target, relation, reportErrors ? reportError : undefined)) return Ternary.True;
 
-                if (source.flags & TypeFlags.Index) {
-                    // A keyof T is related to a union type containing both string and number
-                    const related = relation === comparableRelation ?
-                        maybeTypeOfKind(target, TypeFlags.String | TypeFlags.Number) :
-                        maybeTypeOfKind(target, TypeFlags.String) && maybeTypeOfKind(target, TypeFlags.Number);
-                    if (related) {
-                        return Ternary.True;
-                    }
-                }
-
                 if (getObjectFlags(source) & ObjectFlags.ObjectLiteral && source.flags & TypeFlags.FreshLiteral) {
                     if (hasExcessProperties(<FreshObjectLiteralType>source, target, reportErrors)) {
                         if (reportErrors) {
@@ -15654,7 +15642,7 @@ namespace ts {
             const type = <MappedType>getTypeFromMappedTypeNode(node);
             const constraintType = getConstraintTypeFromMappedType(type);
             const keyType = constraintType.flags & TypeFlags.TypeParameter ? getApparentTypeOfTypeParameter(<TypeParameter>constraintType) : constraintType;
-            checkTypeAssignableTo(keyType, stringOrNumberType, node.typeParameter.constraint);
+            checkTypeAssignableTo(keyType, stringType, node.typeParameter.constraint);
         }
 
         function isPrivateWithinAmbient(node: Node): boolean {

src/compiler/types.ts

@@ -2789,7 +2789,7 @@ namespace ts {
         Intrinsic = Any | String | Number | Boolean | BooleanLiteral | ESSymbol | Void | Undefined | Null | Never,
         /* @internal */
         Primitive = String | Number | Boolean | Enum | ESSymbol | Void | Undefined | Null | Literal,
-        StringLike = String | StringLiteral,
+        StringLike = String | StringLiteral | Index,
         NumberLike = Number | NumberLiteral | Enum | EnumLiteral,
         BooleanLike = Boolean | BooleanLiteral,
         EnumLike = Enum | EnumLiteral,

src/lib/es5.d.ts

@@ -1367,7 +1367,7 @@ type Pick<T, K extends keyof T> = {
 /**
  * Construct a type with a set of properties K of type T
  */
-type Record<K extends string | number, T> = {
+type Record<K extends string, T> = {
     [P in K]: T;
 }
 

tests/baselines/reference/for-inStatements.errors.txt

@@ -1,7 +1,9 @@
+tests/cases/conformance/statements/for-inStatements/for-inStatements.ts(33,18): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
+tests/cases/conformance/statements/for-inStatements/for-inStatements.ts(50,18): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
 tests/cases/conformance/statements/for-inStatements/for-inStatements.ts(79,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
 
 
-==== tests/cases/conformance/statements/for-inStatements/for-inStatements.ts (1 errors) ====
+==== tests/cases/conformance/statements/for-inStatements/for-inStatements.ts (3 errors) ====
     var aString: string;
     for (aString in {}) { }
 
@@ -35,6 +37,8 @@ tests/cases/conformance/statements/for-inStatements/for-inStatements.ts(79,15):
             for (var x in this.biz()) { }
             for (var x in this.biz) { }
             for (var x in this) { }
+                     ~
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
             return null;
         }
 
@@ -52,6 +56,8 @@ tests/cases/conformance/statements/for-inStatements/for-inStatements.ts(79,15):
             for (var x in this.biz()) { }
             for (var x in this.biz) { }
             for (var x in this) { }
+                     ~
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
 
             for (var x in super.biz) { }
             for (var x in super.biz()) { }

tests/baselines/reference/for-inStatementsInvalid.errors.txt

@@ -9,13 +9,15 @@ tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(1
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(20,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(22,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(29,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(31,18): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(38,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(46,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(48,18): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(51,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(62,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
 
 
-==== tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts (15 errors) ====
+==== tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts (17 errors) ====
     var aNumber: number;
     for (aNumber in {}) { }
          ~~~~~~~
@@ -69,6 +71,8 @@ tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(6
 !!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
             for (var x in this.biz) { }
             for (var x in this) { }
+                     ~
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
             return null;
         }
 
@@ -90,6 +94,8 @@ tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(6
 !!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
             for (var x in this.biz) { }
             for (var x in this) { }
+                     ~
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
 
             for (var x in super.biz) { }
             for (var x in super.biz()) { }

tests/baselines/reference/forInStatement3.types

@@ -8,7 +8,7 @@ function F<T>() {
 >T : T
 
   for (var a in expr) {
->a : string
+>a : keyof T
 >expr : T
   }
 }

tests/baselines/reference/implicitAnyInCatch.types

@@ -22,7 +22,7 @@ class C {
 >temp : () => void
 
         for (var x in this) {
->x : string
+>x : keyof this
 >this : this
         }
     }

tests/baselines/reference/inOperatorWithGeneric.types

@@ -9,7 +9,7 @@ class C<T> {
 >T : T
 
         for (var p in x) {
->p : string
+>p : keyof T
 >x : T
         }
     }

tests/baselines/reference/keyofAndIndexedAccess.js

@@ -95,22 +95,18 @@ function f10(shape: Shape) {
 
 function f11(a: Shape[]) {
     let len = getProperty(a, "length");  // number
-    let shape = getProperty(a, 1000);    // Shape
-    setProperty(a, 1000, getProperty(a, 1001));
+    setProperty(a, "length", len);
 }
 
 function f12(t: [Shape, boolean]) {
     let len = getProperty(t, "length");
-    let s1 = getProperty(t, 0);    // Shape
     let s2 = getProperty(t, "0");  // Shape
-    let b1 = getProperty(t, 1);    // boolean
     let b2 = getProperty(t, "1");  // boolean
-    let x1 = getProperty(t, 2);    // Shape | boolean
 }
 
 function f13(foo: any, bar: any) {
     let x = getProperty(foo, "x");  // any
-    let y = getProperty(foo, 100);  // any
+    let y = getProperty(foo, "100");  // any
     let z = getProperty(foo, bar);  // any
 }
 
@@ -181,20 +177,14 @@ function f40(c: C) {
     let z: Z = c["z"];
 }
 
-function f50<T>(k: keyof T, s: string, n: number) {
+function f50<T>(k: keyof T, s: string) {
     const x1 = s as keyof T;
-    const x2 = n as keyof T;
-    const x3 = k as string;
-    const x4 = k as number;
-    const x5 = k as string | number;
+    const x2 = k as string;
 }
 
-function f51<T, K extends keyof T>(k: K, s: string, n: number) {
+function f51<T, K extends keyof T>(k: K, s: string) {
     const x1 = s as keyof T;
-    const x2 = n as keyof T;
-    const x3 = k as string;
-    const x4 = k as number;
-    const x5 = k as string | number;
+    const x2 = k as string;
 }
 
 function f52<T>(obj: { [x: string]: boolean }, k: keyof T, s: string, n: number) {
@@ -221,6 +211,12 @@ function f55<T, K extends keyof T>(obj: T, key: K) {
     const b = "foo" in obj[key];
 }
 
+function f60<T>(source: T, target: T) {
+    for (let k in source) {
+        target[k] = source[k];
+    }
+}
+
 // Repros from #12011
 
 class Base {
@@ -297,20 +293,16 @@ function f10(shape) {
 }
 function f11(a) {
     var len = getProperty(a, "length"); // number
-    var shape = getProperty(a, 1000); // Shape
-    setProperty(a, 1000, getProperty(a, 1001));
+    setProperty(a, "length", len);
 }
 function f12(t) {
     var len = getProperty(t, "length");
-    var s1 = getProperty(t, 0); // Shape
     var s2 = getProperty(t, "0"); // Shape
-    var b1 = getProperty(t, 1); // boolean
     var b2 = getProperty(t, "1"); // boolean
-    var x1 = getProperty(t, 2); // Shape | boolean
 }
 function f13(foo, bar) {
     var x = getProperty(foo, "x"); // any
-    var y = getProperty(foo, 100); // any
+    var y = getProperty(foo, "100"); // any
     var z = getProperty(foo, bar); // any
 }
 var Component = (function () {
@@ -369,19 +361,13 @@ function f40(c) {
     var y = c["y"];
     var z = c["z"];
 }
-function f50(k, s, n) {
+function f50(k, s) {
     var x1 = s;
-    var x2 = n;
-    var x3 = k;
-    var x4 = k;
-    var x5 = k;
+    var x2 = k;
 }
-function f51(k, s, n) {
+function f51(k, s) {
     var x1 = s;
-    var x2 = n;
-    var x3 = k;
-    var x4 = k;
-    var x5 = k;
+    var x2 = k;
 }
 function f52(obj, k, s, n) {
     var x1 = obj[s];
@@ -403,6 +389,11 @@ function f55(obj, key) {
     }
     var b = "foo" in obj[key];
 }
+function f60(source, target) {
+    for (var k in source) {
+        target[k] = source[k];
+    }
+}
 // Repros from #12011
 var Base = (function () {
     function Base() {
@@ -528,8 +519,8 @@ declare class C {
     private z;
 }
 declare function f40(c: C): void;
-declare function f50<T>(k: keyof T, s: string, n: number): void;
-declare function f51<T, K extends keyof T>(k: K, s: string, n: number): void;
+declare function f50<T>(k: keyof T, s: string): void;
+declare function f51<T, K extends keyof T>(k: K, s: string): void;
 declare function f52<T>(obj: {
     [x: string]: boolean;
 }, k: keyof T, s: string, n: number): void;
@@ -538,6 +529,7 @@ declare function f53<T, K extends keyof T>(obj: {
 }, k: K, s: string, n: number): void;
 declare function f54<T>(obj: T, key: keyof T): void;
 declare function f55<T, K extends keyof T>(obj: T, key: K): void;
+declare function f60<T>(source: T, target: T): void;
 declare class Base {
     get<K extends keyof this>(prop: K): this[K];
     set<K extends keyof this>(prop: K, value: this[K]): void;