Preserve type aliases for union and intersection types (microsoft#42149)

* Create separate types for equivalent aliased unions

* Accept new baselines

* Preserve original types for union types

* Accept new baselines

* Preserve intersection origin for union types

* Accept new baselines

* Accept new baselines

* Preserve aliases during relationship checks

* Accept new baselines

* Preserve aliases for intersection and indexed access types

* Accept new baselines

* Compute intersection-of-unions cross product without recursion

* Accept new baselines

* Use denormalized type objects for origin / support 'keyof' origins

* Accept new baselines

* Fix fourslash test

* Recursively extract named union types

* Accept new baselines

* Map on union origin in mapType to better preserve aliases and origins

* Remove redundant call

* Accept new baselines

* Revert back to declared type when branches produce equivalent union

* Accept new baselines

* Don't include denormal origin types in regular type statistics

* Fix issue with unions not being marked primitive-only

* Allow new alias to be associated with type alias instantiation

* Accept new baselines

* Revert "Accept new baselines"

This reverts commit 4507270.

* Revert "Allow new alias to be associated with type alias instantiation"

This reverts commit 2c2d06d.

Author: ahejlsberg

src/compiler/checker.ts

@@ -5008,7 +5008,7 @@ namespace ts {
         // This *should* be every type other than null, undefined, void, and never
         Narrowable = Any | Unknown | StructuredOrInstantiable | StringLike | NumberLike | BigIntLike | BooleanLike | ESSymbol | UniqueESSymbol | NonPrimitive,
         /* @internal */
-        NotPrimitiveUnion = Any | Unknown | Enum | Void | Never | StructuredOrInstantiable,
+        NotPrimitiveUnion = Any | Unknown | Enum | Void | Never | Object | Intersection | Instantiable,
         // The following flags are aggregated during union and intersection type construction
         /* @internal */
         IncludesMask = Any | Unknown | Primitive | Never | Object | Union | Intersection | NonPrimitive | TemplateLiteral,
@@ -5296,9 +5296,11 @@ namespace ts {
 
     export interface UnionType extends UnionOrIntersectionType {
         /* @internal */
-        resolvedReducedType: Type;
+        resolvedReducedType?: Type;
         /* @internal */
-        regularType: UnionType;
+        regularType?: UnionType;
+        /* @internal */
+        origin?: Type;  // Denormalized union, intersection, or index type in which union originates
     }
 
     export interface IntersectionType extends UnionOrIntersectionType {

src/compiler/types.ts

@@ -49,8 +49,8 @@ animal.canMeow; // since is cat, should not be an error
 >canMeow : true
 
 const animalOrUndef = { type: 'cat', canMeow: true } as Animal | undefined;
->animalOrUndef : Cat | Dog | undefined
->{ type: 'cat', canMeow: true } as Animal | undefined : Cat | Dog | undefined
+>animalOrUndef : Animal | undefined
+>{ type: 'cat', canMeow: true } as Animal | undefined : Animal | undefined
 >{ type: 'cat', canMeow: true } : { type: "cat"; canMeow: true; }
 >type : "cat"
 >'cat' : "cat"
@@ -61,7 +61,7 @@ assertEqual(animalOrUndef?.type, 'cat' as const);
 >assertEqual(animalOrUndef?.type, 'cat' as const) : void
 >assertEqual : <T>(value: any, type: T) => asserts value is T
 >animalOrUndef?.type : "cat" | "dog" | undefined
->animalOrUndef : Cat | Dog | undefined
+>animalOrUndef : Animal | undefined
 >type : "cat" | "dog" | undefined
 >'cat' as const : "cat"
 >'cat' : "cat"

tests/baselines/reference/assertionFunctionsCanNarrowByDiscriminant.types

@@ -6,9 +6,9 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithDiscriminatedUnion.ts(58,5): error TS2322: Type 'S' is not assignable to type 'T'.
   Property 'c' is missing in type 'S' but required in type '{ a: 2; b: 4 | 3; c: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithDiscriminatedUnion.ts(82,5): error TS2322: Type 'S' is not assignable to type 'T'.
-  Type 'S' is not assignable to type '{ a: 0 | 2 | 1; b: 0 | 2 | 1; c: 2; }'.
+  Type 'S' is not assignable to type '{ a: N; b: N; c: 2; }'.
     Types of property 'c' are incompatible.
-      Type '0 | 2 | 1' is not assignable to type '2'.
+      Type 'N' is not assignable to type '2'.
         Type '0' is not assignable to type '2'.
 
 
@@ -107,9 +107,9 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         t = s;
         ~
 !!! error TS2322: Type 'S' is not assignable to type 'T'.
-!!! error TS2322:   Type 'S' is not assignable to type '{ a: 0 | 2 | 1; b: 0 | 2 | 1; c: 2; }'.
+!!! error TS2322:   Type 'S' is not assignable to type '{ a: N; b: N; c: 2; }'.
 !!! error TS2322:     Types of property 'c' are incompatible.
-!!! error TS2322:       Type '0 | 2 | 1' is not assignable to type '2'.
+!!! error TS2322:       Type 'N' is not assignable to type '2'.
 !!! error TS2322:         Type '0' is not assignable to type '2'.
     }
 

tests/baselines/reference/assignmentCompatWithDiscriminatedUnion.errors.txt

@@ -155,58 +155,58 @@ namespace Example5 {
     //       3 discriminant properties with 3 types a piece
     //       is 27 possible combinations.
     type N = 0 | 1 | 2;
->N : 0 | 2 | 1
+>N : N
 
     type S = { a: N, b: N, c: N };
 >S : S
->a : 0 | 2 | 1
->b : 0 | 2 | 1
->c : 0 | 2 | 1
+>a : N
+>b : N
+>c : N
 
     type T = { a: 0, b: N, c: N }
 >T : T
 >a : 0
->b : 0 | 2 | 1
->c : 0 | 2 | 1
+>b : N
+>c : N
 
            | { a: 1, b: N, c: N }
 >a : 1
->b : 0 | 2 | 1
->c : 0 | 2 | 1
+>b : N
+>c : N
 
            | { a: 2, b: N, c: N }
 >a : 2
->b : 0 | 2 | 1
->c : 0 | 2 | 1
+>b : N
+>c : N
 
            | { a: N, b: 0, c: N }
->a : 0 | 2 | 1
+>a : N
 >b : 0
->c : 0 | 2 | 1
+>c : N
 
            | { a: N, b: 1, c: N }
->a : 0 | 2 | 1
+>a : N
 >b : 1
->c : 0 | 2 | 1
+>c : N
 
            | { a: N, b: 2, c: N }
->a : 0 | 2 | 1
+>a : N
 >b : 2
->c : 0 | 2 | 1
+>c : N
 
            | { a: N, b: N, c: 0 }
->a : 0 | 2 | 1
->b : 0 | 2 | 1
+>a : N
+>b : N
 >c : 0
 
            | { a: N, b: N, c: 1 }
->a : 0 | 2 | 1
->b : 0 | 2 | 1
+>a : N
+>b : N
 >c : 1
 
            | { a: N, b: N, c: 2 };
->a : 0 | 2 | 1
->b : 0 | 2 | 1
+>a : N
+>b : N
 >c : 2
 
     declare let s: S;
@@ -359,9 +359,9 @@ namespace GH12052 {
 
     good.type = getAxisType();
 >good.type = getAxisType() : IAxisType
->good.type : IAxisType
+>good.type : "linear" | "categorical"
 >good : IAxis
->type : IAxisType
+>type : "linear" | "categorical"
 >getAxisType() : IAxisType
 >getAxisType : () => IAxisType
 }
@@ -473,17 +473,17 @@ namespace GH39357 {
 >A : A
 
     type B = "a" | "b" | "c";
->B : "a" | "b" | "c"
+>B : B
 
     declare const b: B;
->b : "a" | "b" | "c"
+>b : B
 
     const a: A = b === "a" || b === "b" ? [b, 1] : ["c", ""];
 >a : A
 >b === "a" || b === "b" ? [b, 1] : ["c", ""] : ["a" | "b", number] | ["c", string]
 >b === "a" || b === "b" : boolean
 >b === "a" : boolean
->b : "a" | "b" | "c"
+>b : B
 >"a" : "a"
 >b === "b" : boolean
 >b : "b" | "c"

tests/baselines/reference/assignmentCompatWithDiscriminatedUnion.types

@@ -1,30 +1,30 @@
 === tests/cases/conformance/types/literal/booleanLiteralTypes1.ts ===
 type A1 = true | false;
->A1 : boolean
+>A1 : A1
 >true : true
 >false : false
 
 type A2 = false | true;
->A2 : boolean
+>A2 : A2
 >false : false
 >true : true
 
 function f1() {
 >f1 : () => void
 
     var a: A1;
->a : boolean
+>a : A1
 
     var a: A2;
->a : boolean
+>a : A1
 
     var a: true | false;
->a : boolean
+>a : A1
 >true : true
 >false : false
 
     var a: false | true;
->a : boolean
+>a : A1
 >false : false
 >true : true
 }

tests/baselines/reference/booleanLiteralTypes1.types

@@ -1,30 +1,30 @@
 === tests/cases/conformance/types/literal/booleanLiteralTypes2.ts ===
 type A1 = true | false;
->A1 : boolean
+>A1 : A1
 >true : true
 >false : false
 
 type A2 = false | true;
->A2 : boolean
+>A2 : A2
 >false : false
 >true : true
 
 function f1() {
 >f1 : () => void
 
     var a: A1;
->a : boolean
+>a : A1
 
     var a: A2;
->a : boolean
+>a : A1
 
     var a: true | false;
->a : boolean
+>a : A1
 >true : true
 >false : false
 
     var a: false | true;
->a : boolean
+>a : A1
 >false : false
 >true : true
 }

tests/baselines/reference/booleanLiteralTypes2.types

@@ -30,8 +30,8 @@ function test1() {
 >t : Temp1 | Temp2
 
         const z = t.getValue("bar"); // Should be fine
->z : React.ReactText
->t.getValue("bar") : React.ReactText
+>z : string | number
+>t.getValue("bar") : string | number
 >t.getValue : ((name: "foo" | "bar") => number) | ((name: "bar" | "baz") => string)
 >t : Temp1 | Temp2
 >getValue : ((name: "foo" | "bar") => number) | ((name: "bar" | "baz") => string)
@@ -399,7 +399,7 @@ function test5() {
         }
 
         var C: React.ComponentType<P1> | React.ComponentType<P2> = null as any;
->C : React.ComponentClass<P1, any> | React.StatelessComponent<P1> | React.ComponentClass<P2, any> | React.StatelessComponent<P2>
+>C : React.ComponentType<P1> | React.ComponentType<P2>
 >React : any
 >React : any
 >null as any : any
@@ -408,7 +408,7 @@ function test5() {
         const a = <C p={true} />;
 >a : JSX.Element
 ><C p={true} /> : JSX.Element
->C : React.ComponentClass<P1, any> | React.StatelessComponent<P1> | React.ComponentClass<P2, any> | React.StatelessComponent<P2>
+>C : React.ComponentType<P1> | React.ComponentType<P2>
 >p : true
 >true : true
     }