Print unions resulting from keyof operations with keyof if possible

src/compiler/types.ts

@@ -3490,6 +3490,7 @@ namespace ts {
         /* @internal */
         JsxAttributes           = 1 << 26,  // Jsx attributes type
         MarkerType              = 1 << 27,  // Marker type used for variance probing
+        Alias                   = 1 << 28,  // Placeholder type used to point at another type
 
         /* @internal */
         Nullable = Undefined | Null,
@@ -3534,8 +3535,12 @@ namespace ts {
         /* @internal */ checker: TypeChecker;
         symbol?: Symbol;                 // Symbol associated with type (if any)
         pattern?: DestructuringPattern;  // Destructuring pattern represented by type (if any)
-        aliasSymbol?: Symbol;            // Alias associated with type
-        aliasTypeArguments?: Type[];     // Alias type arguments (if any)
+        alternativeRepresentation?: Type; // Alternative representation of the type, prefered when printing; not to be used for comparisons or equality
+    }
+
+    export interface AliasType extends Type {
+        symbol: Symbol;
+        typeArguments?: Type[];
     }
 
     /* @internal */

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

@@ -2046,6 +2046,7 @@ declare namespace ts {
         IndexedAccess = 1048576,
         NonPrimitive = 33554432,
         MarkerType = 134217728,
+        Alias = 268435456,
         Literal = 224,
         Unit = 13536,
         StringOrNumberLiteral = 96,
@@ -2067,8 +2068,11 @@ declare namespace ts {
         flags: TypeFlags;
         symbol?: Symbol;
         pattern?: DestructuringPattern;
-        aliasSymbol?: Symbol;
-        aliasTypeArguments?: Type[];
+        alternativeRepresentation?: Type;
+    }
+    interface AliasType extends Type {
+        symbol: Symbol;
+        typeArguments?: Type[];
     }
     interface LiteralType extends Type {
         value: string | number;

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

@@ -2046,6 +2046,7 @@ declare namespace ts {
         IndexedAccess = 1048576,
         NonPrimitive = 33554432,
         MarkerType = 134217728,
+        Alias = 268435456,
         Literal = 224,
         Unit = 13536,
         StringOrNumberLiteral = 96,
@@ -2067,8 +2068,11 @@ declare namespace ts {
         flags: TypeFlags;
         symbol?: Symbol;
         pattern?: DestructuringPattern;
-        aliasSymbol?: Symbol;
-        aliasTypeArguments?: Type[];
+        alternativeRepresentation?: Type;
+    }
+    interface AliasType extends Type {
+        symbol: Symbol;
+        typeArguments?: Type[];
     }
     interface LiteralType extends Type {
         value: string | number;

tests/baselines/reference/declarationUsesKeyofAliasWherePossible.js

@@ -0,0 +1,35 @@
+//// [declarationUsesKeyofAliasWherePossible.ts]
+var Foo = class Foo {
+    method<T extends keyof ElementTagNameMap>() {};
+}
+
+class Bar {
+    method<T extends keyof ElementTagNameMap>() {};
+}
+
+//// [declarationUsesKeyofAliasWherePossible.js]
+var Foo = /** @class */ (function () {
+    function Foo() {
+    }
+    Foo.prototype.method = function () { };
+    ;
+    return Foo;
+}());
+var Bar = /** @class */ (function () {
+    function Bar() {
+    }
+    Bar.prototype.method = function () { };
+    ;
+    return Bar;
+}());
+
+
+//// [declarationUsesKeyofAliasWherePossible.d.ts]
+declare var Foo: {
+    new (): {
+        method<T extends keyof ElementTagNameMap>(): void;
+    };
+};
+declare class Bar {
+    method<T extends keyof ElementTagNameMap>(): void;
+}

tests/baselines/reference/declarationUsesKeyofAliasWherePossible.symbols

@@ -0,0 +1,19 @@
+=== tests/cases/compiler/declarationUsesKeyofAliasWherePossible.ts ===
+var Foo = class Foo {
+>Foo : Symbol(Foo, Decl(declarationUsesKeyofAliasWherePossible.ts, 0, 3))
+>Foo : Symbol(Foo, Decl(declarationUsesKeyofAliasWherePossible.ts, 0, 9))
+
+    method<T extends keyof ElementTagNameMap>() {};
+>method : Symbol(Foo.method, Decl(declarationUsesKeyofAliasWherePossible.ts, 0, 21))
+>T : Symbol(T, Decl(declarationUsesKeyofAliasWherePossible.ts, 1, 11))
+>ElementTagNameMap : Symbol(ElementTagNameMap, Decl(lib.dom.d.ts, --, --))
+}
+
+class Bar {
+>Bar : Symbol(Bar, Decl(declarationUsesKeyofAliasWherePossible.ts, 2, 1))
+
+    method<T extends keyof ElementTagNameMap>() {};
+>method : Symbol(Bar.method, Decl(declarationUsesKeyofAliasWherePossible.ts, 4, 11))
+>T : Symbol(T, Decl(declarationUsesKeyofAliasWherePossible.ts, 5, 11))
+>ElementTagNameMap : Symbol(ElementTagNameMap, Decl(lib.dom.d.ts, --, --))
+}

tests/baselines/reference/declarationUsesKeyofAliasWherePossible.types

@@ -0,0 +1,20 @@
+=== tests/cases/compiler/declarationUsesKeyofAliasWherePossible.ts ===
+var Foo = class Foo {
+>Foo : typeof Foo
+>class Foo {    method<T extends keyof ElementTagNameMap>() {};} : typeof Foo
+>Foo : typeof Foo
+
+    method<T extends keyof ElementTagNameMap>() {};
+>method : <T extends keyof ElementTagNameMap>() => void
+>T : T
+>ElementTagNameMap : ElementTagNameMap
+}
+
+class Bar {
+>Bar : Bar
+
+    method<T extends keyof ElementTagNameMap>() {};
+>method : <T extends keyof ElementTagNameMap>() => void
+>T : T
+>ElementTagNameMap : ElementTagNameMap
+}

tests/baselines/reference/doubleUnderscoreMappedTypes.types

@@ -27,12 +27,12 @@ const ok: Properties = {
 
 // As expected, "__property2" is indeed a key of the type
 type Keys = keyof Properties;
->Keys : "property1" | "__property2"
+>Keys : keyof Properties
 >Properties : Properties
 
 const k: Keys = "__property2"; // ok
->k : "property1" | "__property2"
->Keys : "property1" | "__property2"
+>k : keyof Properties
+>Keys : keyof Properties
 >"__property2" : "__property2"
 
 // This should be valid

tests/baselines/reference/indirectTypeParameterReferences.js

@@ -47,3 +47,22 @@ combined(function (comb) {
     comb.a;
 });
 var n = f(2).a;
+
+
+//// [indirectTypeParameterReferences.d.ts]
+declare type B = {
+    b: string;
+};
+declare const flowtypes: <A>(b: B) => {
+    combined: (fn: (combined: A & B) => void) => any;
+    literal: (fn: (aPlusB: A & B) => void) => any;
+};
+declare const combined: (fn: (combined: {
+    a: string;
+} & B) => void) => any, literal: (fn: (aPlusB: {
+    a: string;
+} & B) => void) => any;
+declare function f<T>(a: T): {
+    a: typeof a;
+};
+declare let n: number;

tests/baselines/reference/keyofAndIndexedAccess.types

@@ -84,11 +84,11 @@ type K07 = keyof never;  // never
 >K07 : never
 
 type K10 = keyof Shape;  // "name" | "width" | "height" | "visible"
->K10 : "name" | "width" | "height" | "visible"
+>K10 : keyof Shape
 >Shape : Shape
 
 type K11 = keyof Shape[];  // "length" | "toString" | ...
->K11 : "length" | "toString" | "toLocaleString" | "push" | "pop" | "concat" | "join" | "reverse" | "shift" | "slice" | "sort" | "splice" | "unshift" | "indexOf" | "lastIndexOf" | "every" | "some" | "forEach" | "map" | "filter" | "reduce" | "reduceRight"
+>K11 : keyof Shape[]
 >Shape : Shape
 
 type K12 = keyof Dictionary<Shape>;  // string
@@ -100,7 +100,7 @@ type K13 = keyof {};  // never
 >K13 : never
 
 type K14 = keyof Object;  // "constructor" | "toString" | ...
->K14 : "toString" | "toLocaleString" | "valueOf" | "constructor" | "hasOwnProperty" | "isPrototypeOf" | "propertyIsEnumerable"
+>K14 : keyof Object
 >Object : Object
 
 type K15 = keyof E;  // "toString" | "toFixed" | "toExponential" | ...
@@ -131,7 +131,7 @@ type KeyOf<T> = keyof T;
 >T : T
 
 type K20 = KeyOf<Shape>;  // "name" | "width" | "height" | "visible"
->K20 : "name" | "width" | "height" | "visible"
+>K20 : keyof Shape
 >KeyOf : keyof T
 >Shape : Shape
 
@@ -452,17 +452,17 @@ function f20(component: Component<Shape>) {
     let name = component.getProperty("name");  // string
 >name : string
 >component.getProperty("name") : string
->component.getProperty : <K extends "name" | "width" | "height" | "visible">(key: K) => Shape[K]
+>component.getProperty : <K extends keyof Shape>(key: K) => Shape[K]
 >component : Component<Shape>
->getProperty : <K extends "name" | "width" | "height" | "visible">(key: K) => Shape[K]
+>getProperty : <K extends keyof Shape>(key: K) => Shape[K]
 >"name" : "name"
 
     let widthOrHeight = component.getProperty(cond ? "width" : "height");  // number
 >widthOrHeight : number
 >component.getProperty(cond ? "width" : "height") : number
->component.getProperty : <K extends "name" | "width" | "height" | "visible">(key: K) => Shape[K]
+>component.getProperty : <K extends keyof Shape>(key: K) => Shape[K]
 >component : Component<Shape>
->getProperty : <K extends "name" | "width" | "height" | "visible">(key: K) => Shape[K]
+>getProperty : <K extends keyof Shape>(key: K) => Shape[K]
 >cond ? "width" : "height" : "width" | "height"
 >cond : boolean
 >"width" : "width"
@@ -471,27 +471,27 @@ function f20(component: Component<Shape>) {
     let nameOrVisible = component.getProperty(cond ? "name" : "visible");  // string | boolean
 >nameOrVisible : string | boolean
 >component.getProperty(cond ? "name" : "visible") : string | boolean
->component.getProperty : <K extends "name" | "width" | "height" | "visible">(key: K) => Shape[K]
+>component.getProperty : <K extends keyof Shape>(key: K) => Shape[K]
 >component : Component<Shape>
->getProperty : <K extends "name" | "width" | "height" | "visible">(key: K) => Shape[K]
+>getProperty : <K extends keyof Shape>(key: K) => Shape[K]
 >cond ? "name" : "visible" : "name" | "visible"
 >cond : boolean
 >"name" : "name"
 >"visible" : "visible"
 
     component.setProperty("name", "rectangle");
 >component.setProperty("name", "rectangle") : void
->component.setProperty : <K extends "name" | "width" | "height" | "visible">(key: K, value: Shape[K]) => void
+>component.setProperty : <K extends keyof Shape>(key: K, value: Shape[K]) => void
 >component : Component<Shape>
->setProperty : <K extends "name" | "width" | "height" | "visible">(key: K, value: Shape[K]) => void
+>setProperty : <K extends keyof Shape>(key: K, value: Shape[K]) => void
 >"name" : "name"
 >"rectangle" : "rectangle"
 
     component.setProperty(cond ? "width" : "height", 10)
 >component.setProperty(cond ? "width" : "height", 10) : void
->component.setProperty : <K extends "name" | "width" | "height" | "visible">(key: K, value: Shape[K]) => void
+>component.setProperty : <K extends keyof Shape>(key: K, value: Shape[K]) => void
 >component : Component<Shape>
->setProperty : <K extends "name" | "width" | "height" | "visible">(key: K, value: Shape[K]) => void
+>setProperty : <K extends keyof Shape>(key: K, value: Shape[K]) => void
 >cond ? "width" : "height" : "width" | "height"
 >cond : boolean
 >"width" : "width"
@@ -500,9 +500,9 @@ function f20(component: Component<Shape>) {
 
     component.setProperty(cond ? "name" : "visible", true);  // Technically not safe
 >component.setProperty(cond ? "name" : "visible", true) : void
->component.setProperty : <K extends "name" | "width" | "height" | "visible">(key: K, value: Shape[K]) => void
+>component.setProperty : <K extends keyof Shape>(key: K, value: Shape[K]) => void
 >component : Component<Shape>
->setProperty : <K extends "name" | "width" | "height" | "visible">(key: K, value: Shape[K]) => void
+>setProperty : <K extends keyof Shape>(key: K, value: Shape[K]) => void
 >cond ? "name" : "visible" : "name" | "visible"
 >cond : boolean
 >"name" : "name"
@@ -563,7 +563,7 @@ function f30(shapes: Shape[]) {
 }
 
 function f31<K extends keyof Shape>(key: K) {
->f31 : <K extends "name" | "width" | "height" | "visible">(key: K) => Shape[K]
+>f31 : <K extends keyof Shape>(key: K) => Shape[K]
 >K : K
 >Shape : Shape
 >key : K

tests/baselines/reference/keyofAndIndexedAccessErrors.errors.txt

@@ -16,12 +16,12 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(36,21): error
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(41,31): error TS2538: Type 'boolean' cannot be used as an index type.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(46,16): error TS2538: Type 'boolean' cannot be used as an index type.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(49,12): error TS1122: A tuple type element list cannot be empty.
-tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(63,33): error TS2345: Argument of type '"size"' is not assignable to parameter of type '"name" | "width" | "height" | "visible"'.
-tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(64,33): error TS2345: Argument of type '"name" | "size"' is not assignable to parameter of type '"name" | "width" | "height" | "visible"'.
-  Type '"size"' is not assignable to type '"name" | "width" | "height" | "visible"'.
-tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(66,24): error TS2345: Argument of type '"size"' is not assignable to parameter of type '"name" | "width" | "height" | "visible"'.
-tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(67,24): error TS2345: Argument of type '"name" | "size"' is not assignable to parameter of type '"name" | "width" | "height" | "visible"'.
-  Type '"size"' is not assignable to type '"name" | "width" | "height" | "visible"'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(63,33): error TS2345: Argument of type '"size"' is not assignable to parameter of type 'keyof Shape'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(64,33): error TS2345: Argument of type '"name" | "size"' is not assignable to parameter of type 'keyof Shape'.
+  Type '"size"' is not assignable to type 'keyof Shape'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(66,24): error TS2345: Argument of type '"size"' is not assignable to parameter of type 'keyof Shape'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(67,24): error TS2345: Argument of type '"name" | "size"' is not assignable to parameter of type 'keyof Shape'.
+  Type '"size"' is not assignable to type 'keyof Shape'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(72,5): error TS2536: Type 'keyof (T & U)' cannot be used to index type 'T | U'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(76,5): error TS2322: Type 'T | U' is not assignable to type 'T & U'.
   Type 'T' is not assignable to type 'T & U'.
@@ -132,19 +132,19 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(85,9): error
         let x1 = getProperty(shape, "name");
         let x2 = getProperty(shape, "size");  // Error
                                     ~~~~~~
-!!! error TS2345: Argument of type '"size"' is not assignable to parameter of type '"name" | "width" | "height" | "visible"'.
+!!! error TS2345: Argument of type '"size"' is not assignable to parameter of type 'keyof Shape'.
         let x3 = getProperty(shape, cond ? "name" : "size");  // Error
                                     ~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS2345: Argument of type '"name" | "size"' is not assignable to parameter of type '"name" | "width" | "height" | "visible"'.
-!!! error TS2345:   Type '"size"' is not assignable to type '"name" | "width" | "height" | "visible"'.
+!!! error TS2345: Argument of type '"name" | "size"' is not assignable to parameter of type 'keyof Shape'.
+!!! error TS2345:   Type '"size"' is not assignable to type 'keyof Shape'.
         setProperty(shape, "name", "rectangle");
         setProperty(shape, "size", 10);  // Error
                            ~~~~~~
-!!! error TS2345: Argument of type '"size"' is not assignable to parameter of type '"name" | "width" | "height" | "visible"'.
+!!! error TS2345: Argument of type '"size"' is not assignable to parameter of type 'keyof Shape'.
         setProperty(shape, cond ? "name" : "size", 10);  // Error
                            ~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS2345: Argument of type '"name" | "size"' is not assignable to parameter of type '"name" | "width" | "height" | "visible"'.
-!!! error TS2345:   Type '"size"' is not assignable to type '"name" | "width" | "height" | "visible"'.
+!!! error TS2345: Argument of type '"name" | "size"' is not assignable to parameter of type 'keyof Shape'.
+!!! error TS2345:   Type '"size"' is not assignable to type 'keyof Shape'.
     }
 
     function f20<T, U>(k1: keyof (T | U), k2: keyof (T & U), o1: T | U, o2: T & U) {

tests/baselines/reference/keyofAndIndexedAccessErrors.types

@@ -26,27 +26,27 @@ type T00 = keyof K0;  // Error
 >K0 : No type information available!
 
 type T01 = keyof Object;
->T01 : "toString" | "constructor" | "toLocaleString" | "valueOf" | "hasOwnProperty" | "isPrototypeOf" | "propertyIsEnumerable"
+>T01 : keyof Object
 >Object : Object
 
 type T02 = keyof keyof Object;
->T02 : "length" | "toString" | "valueOf" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
+>T02 : keyof String
 >Object : Object
 
 type T03 = keyof keyof keyof Object;
->T03 : "length" | "toString" | "valueOf" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
+>T03 : keyof String
 >Object : Object
 
 type T04 = keyof keyof keyof keyof Object;
->T04 : "length" | "toString" | "valueOf" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
+>T04 : keyof String
 >Object : Object
 
 type T05 = keyof keyof keyof keyof keyof Object;
->T05 : "length" | "toString" | "valueOf" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
+>T05 : keyof String
 >Object : Object
 
 type T06 = keyof keyof keyof keyof keyof keyof Object;
->T06 : "length" | "toString" | "valueOf" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
+>T06 : keyof String
 >Object : Object
 
 type T10 = Shape["name"];