Support re-aliasing of type alias instantiations (#42284)

* New aliases for type alias instantiations

* New aliases for conditional, mapped, and anonymous object type instantiations

* Accept new baselines

* Fix issues with re-aliasing

* Accept new baselines

Author: ahejlsberg

src/compiler/checker.ts

@@ -4745,6 +4745,8 @@ namespace ts {
         typeParameters?: TypeParameter[];           // Type parameters of type alias (undefined if non-generic)
         outerTypeParameters?: TypeParameter[];      // Outer type parameters of anonymous object type
         instantiations?: ESMap<string, Type>;       // Instantiations of generic type alias (undefined if non-generic)
+        aliasSymbol?: Symbol;                       // Alias associated with generic type alias instantiation
+        aliasTypeArguments?: readonly Type[]        // Alias type arguments (if any)
         inferredClassSymbol?: ESMap<SymbolId, TransientSymbol>; // Symbol of an inferred ES5 constructor function
         mapper?: TypeMapper;                        // Type mapper for instantiation alias
         referenced?: boolean;                       // True if alias symbol has been referenced as a value that can be emitted

src/compiler/types.ts

@@ -8,10 +8,10 @@ type ExtendedMapper<HandledInputT, OutputT, ArgsT extends any[]> = (name : strin
 >args : ArgsT
 
 type a = ExtendedMapper<any, any, [any]>;
->a : ExtendedMapper<any, any, [any]>
+>a : a
 
 type b = ExtendedMapper<any, any, any[]>;
->b : ExtendedMapper<any, any, any[]>
+>b : b
 
 type test = a extends b ? "y" : "n"
 >test : "y"
@@ -32,10 +32,10 @@ type ExtendedMapper1<HandledInputT, OutputT, ArgsT extends any[]> = (
 );
 
 type a1 = ExtendedMapper1<any, any, [any]>;
->a1 : ExtendedMapper1<any, any, [any]>
+>a1 : a1
 
 type b1 = ExtendedMapper1<any, any, any[]>;
->b1 : ExtendedMapper1<any, any, any[]>
+>b1 : b1
 
 type test1 = a1 extends b1 ? "y" : "n"
 >test1 : "y"
@@ -56,10 +56,10 @@ type ExtendedMapper2<HandledInputT, OutputT, ArgsT extends any[]> = (
 );
 
 type a2 = ExtendedMapper2<any, any, [any]>;
->a2 : (name: string, mixed: any, args_0: any) => any
+>a2 : a2
 
 type b2 = ExtendedMapper2<any, any, any[]>;
->b2 : (name: string, mixed: any, ...args: any[]) => any
+>b2 : b2
 
 type test2 = a2 extends b2 ? "y" : "n"
 >test2 : "y"

tests/baselines/reference/aliasOfGenericFunctionWithRestBehavedSameAsUnaliased.types

@@ -60,8 +60,7 @@ export declare type TypeB = Merge<TypeA, {
     b: string;
 }>;
 //// [index.d.ts]
+import { TypeB } from './type-b';
 export declare class Broken {
-    method(): import("./types").Merge<import("./type-a").TypeA, {
-        b: string;
-    }>;
+    method(): TypeB;
 }

tests/baselines/reference/caseInsensitiveFileSystemWithCapsImportTypeDeclarations.js

@@ -6,10 +6,10 @@ export class Broken {
 >Broken : Broken
 
     method () {
->method : () => import("tests/cases/compiler/Uppercased_Dir/src/types").Merge<import("tests/cases/compiler/Uppercased_Dir/src/type-a").TypeA, { b: string; }>
+>method : () => TypeB
 
         return { } as TypeB;
->{ } as TypeB : import("tests/cases/compiler/Uppercased_Dir/src/types").Merge<import("tests/cases/compiler/Uppercased_Dir/src/type-a").TypeA, { b: string; }>
+>{ } as TypeB : TypeB
 >{ } : {}
     }
 }
@@ -21,7 +21,7 @@ import { TypeA } from './type-a';
 >TypeA : any
 
 export type TypeB = Merge<TypeA, {
->TypeB : Merge<TypeA, { b: string; }>
+>TypeB : TypeB
 
     b: string;
 >b : string

tests/baselines/reference/caseInsensitiveFileSystemWithCapsImportTypeDeclarations.types

@@ -113,7 +113,7 @@ export type Matching<InjectedProps, DecorationTargetProps> = {
 };
 
 export type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>;
->Omit : Pick<T, Exclude<keyof T, K>>
+>Omit : Omit<T, K>
 
 export type InferableComponentEnhancerWithProps<TInjectedProps, TNeedsProps> =
 >InferableComponentEnhancerWithProps : InferableComponentEnhancerWithProps<TInjectedProps, TNeedsProps>

tests/baselines/reference/circularlyConstrainedMappedTypeContainingConditionalNoInfiniteInstantiationDepth.types

@@ -1,6 +1,6 @@
 === tests/cases/compiler/circularlySimplifyingConditionalTypesNoCrash.ts ===
 type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>;
->Omit : Pick<T, Exclude<keyof T, K>>
+>Omit : Omit<T, K>
 
 type Shared< // Circularly self constraining type, defered thanks to mapping
 >Shared : Shared<InjectedProps, DecorationTargetProps>

tests/baselines/reference/circularlySimplifyingConditionalTypesNoCrash.types

@@ -29,7 +29,7 @@ export type ChannelType = Channel extends { type: infer R } ? R : never;
 >type : R
 
 type Omit<T, K extends keyof T> = Pick<
->Omit : Pick<T, ({ [P in keyof T]: P; } & { [P in K]: never; } & { [x: string]: never; })[keyof T]>
+>Omit : Omit<T, K>
 
     T,
     ({ [P in keyof T]: P } & { [P in K]: never } & { [x: string]: never })[keyof T]

tests/baselines/reference/complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.types

@@ -13,14 +13,24 @@ tests/cases/conformance/types/conditional/conditionalTypes1.ts(29,5): error TS23
 tests/cases/conformance/types/conditional/conditionalTypes1.ts(30,9): error TS2322: Type 'T["x"]' is not assignable to type 'string'.
   Type 'string | undefined' is not assignable to type 'string'.
     Type 'undefined' is not assignable to type 'string'.
-tests/cases/conformance/types/conditional/conditionalTypes1.ts(103,5): error TS2322: Type 'Pick<T, FunctionPropertyNames<T>>' is not assignable to type 'T'.
-  'T' could be instantiated with an arbitrary type which could be unrelated to 'Pick<T, FunctionPropertyNames<T>>'.
-tests/cases/conformance/types/conditional/conditionalTypes1.ts(104,5): error TS2322: Type 'Pick<T, NonFunctionPropertyNames<T>>' is not assignable to type 'T'.
-  'T' could be instantiated with an arbitrary type which could be unrelated to 'Pick<T, NonFunctionPropertyNames<T>>'.
-tests/cases/conformance/types/conditional/conditionalTypes1.ts(106,5): error TS2322: Type 'Pick<T, NonFunctionPropertyNames<T>>' is not assignable to type 'Pick<T, FunctionPropertyNames<T>>'.
+tests/cases/conformance/types/conditional/conditionalTypes1.ts(103,5): error TS2322: Type 'FunctionProperties<T>' is not assignable to type 'T'.
+  'T' could be instantiated with an arbitrary type which could be unrelated to 'FunctionProperties<T>'.
+tests/cases/conformance/types/conditional/conditionalTypes1.ts(104,5): error TS2322: Type 'NonFunctionProperties<T>' is not assignable to type 'T'.
+  'T' could be instantiated with an arbitrary type which could be unrelated to 'NonFunctionProperties<T>'.
+tests/cases/conformance/types/conditional/conditionalTypes1.ts(106,5): error TS2322: Type 'NonFunctionProperties<T>' is not assignable to type 'FunctionProperties<T>'.
   Type 'FunctionPropertyNames<T>' is not assignable to type 'NonFunctionPropertyNames<T>'.
-tests/cases/conformance/types/conditional/conditionalTypes1.ts(108,5): error TS2322: Type 'Pick<T, FunctionPropertyNames<T>>' is not assignable to type 'Pick<T, NonFunctionPropertyNames<T>>'.
+    Type 'keyof T' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
+      Type 'string | number | symbol' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
+        Type 'string' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
+          Type 'keyof T' is not assignable to type 'never'.
+            Type 'string | number | symbol' is not assignable to type 'never'.
+              Type 'string' is not assignable to type 'never'.
+tests/cases/conformance/types/conditional/conditionalTypes1.ts(108,5): error TS2322: Type 'FunctionProperties<T>' is not assignable to type 'NonFunctionProperties<T>'.
   Type 'NonFunctionPropertyNames<T>' is not assignable to type 'FunctionPropertyNames<T>'.
+    Type 'keyof T' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
+      Type 'string | number | symbol' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
+        Type 'string' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
+          Type 'keyof T' is not assignable to type 'never'.
 tests/cases/conformance/types/conditional/conditionalTypes1.ts(114,5): error TS2322: Type 'keyof T' is not assignable to type 'FunctionPropertyNames<T>'.
   Type 'string | number | symbol' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
     Type 'string' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
@@ -52,7 +62,7 @@ tests/cases/conformance/types/conditional/conditionalTypes1.ts(159,5): error TS2
 tests/cases/conformance/types/conditional/conditionalTypes1.ts(160,5): error TS2322: Type 'T' is not assignable to type 'ZeroOf<T>'.
   Type 'string | number' is not assignable to type 'ZeroOf<T>'.
     Type 'string' is not assignable to type 'ZeroOf<T>'.
-tests/cases/conformance/types/conditional/conditionalTypes1.ts(263,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'z' must be of type 'T1', but here has type 'Foo<T & U>'.
+tests/cases/conformance/types/conditional/conditionalTypes1.ts(263,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'z' must be of type 'T1', but here has type 'T2'.
 tests/cases/conformance/types/conditional/conditionalTypes1.ts(288,43): error TS2322: Type 'T95<U>' is not assignable to type 'T94<U>'.
   Type 'number | boolean' is not assignable to type 'T94<U>'.
     Type 'number' is not assignable to type 'T94<U>'.
@@ -185,22 +195,32 @@ tests/cases/conformance/types/conditional/conditionalTypes1.ts(288,43): error TS
     function f7<T>(x: T, y: FunctionProperties<T>, z: NonFunctionProperties<T>) {
         x = y;  // Error
         ~
-!!! error TS2322: Type 'Pick<T, FunctionPropertyNames<T>>' is not assignable to type 'T'.
-!!! error TS2322:   'T' could be instantiated with an arbitrary type which could be unrelated to 'Pick<T, FunctionPropertyNames<T>>'.
+!!! error TS2322: Type 'FunctionProperties<T>' is not assignable to type 'T'.
+!!! error TS2322:   'T' could be instantiated with an arbitrary type which could be unrelated to 'FunctionProperties<T>'.
         x = z;  // Error
         ~
-!!! error TS2322: Type 'Pick<T, NonFunctionPropertyNames<T>>' is not assignable to type 'T'.
-!!! error TS2322:   'T' could be instantiated with an arbitrary type which could be unrelated to 'Pick<T, NonFunctionPropertyNames<T>>'.
+!!! error TS2322: Type 'NonFunctionProperties<T>' is not assignable to type 'T'.
+!!! error TS2322:   'T' could be instantiated with an arbitrary type which could be unrelated to 'NonFunctionProperties<T>'.
         y = x;
         y = z;  // Error
         ~
-!!! error TS2322: Type 'Pick<T, NonFunctionPropertyNames<T>>' is not assignable to type 'Pick<T, FunctionPropertyNames<T>>'.
+!!! error TS2322: Type 'NonFunctionProperties<T>' is not assignable to type 'FunctionProperties<T>'.
 !!! error TS2322:   Type 'FunctionPropertyNames<T>' is not assignable to type 'NonFunctionPropertyNames<T>'.
+!!! error TS2322:     Type 'keyof T' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
+!!! error TS2322:       Type 'string | number | symbol' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
+!!! error TS2322:         Type 'string' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
+!!! error TS2322:           Type 'keyof T' is not assignable to type 'never'.
+!!! error TS2322:             Type 'string | number | symbol' is not assignable to type 'never'.
+!!! error TS2322:               Type 'string' is not assignable to type 'never'.
         z = x;
         z = y;  // Error
         ~
-!!! error TS2322: Type 'Pick<T, FunctionPropertyNames<T>>' is not assignable to type 'Pick<T, NonFunctionPropertyNames<T>>'.
+!!! error TS2322: Type 'FunctionProperties<T>' is not assignable to type 'NonFunctionProperties<T>'.
 !!! error TS2322:   Type 'NonFunctionPropertyNames<T>' is not assignable to type 'FunctionPropertyNames<T>'.
+!!! error TS2322:     Type 'keyof T' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
+!!! error TS2322:       Type 'string | number | symbol' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
+!!! error TS2322:         Type 'string' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
+!!! error TS2322:           Type 'keyof T' is not assignable to type 'never'.
     }
 
     function f8<T>(x: keyof T, y: FunctionPropertyNames<T>, z: NonFunctionPropertyNames<T>) {
@@ -398,7 +418,7 @@ tests/cases/conformance/types/conditional/conditionalTypes1.ts(288,43): error TS
         var z: T1;
         var z: T2;  // Error, T2 is distributive, T1 isn't
             ~
-!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'z' must be of type 'T1', but here has type 'Foo<T & U>'.
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'z' must be of type 'T1', but here has type 'T2'.
 !!! related TS6203 tests/cases/conformance/types/conditional/conditionalTypes1.ts:262:9: 'z' was also declared here.
     }