Merge pull request #28851 from Microsoft/deferConditionalTypes

Defer resolution of conditional types with generic check or extends types

Author: ahejlsberg

src/compiler/checker.ts

@@ -9785,31 +9785,29 @@ namespace ts {
             if (checkType === wildcardType || extendsType === wildcardType) {
                 return wildcardType;
             }
-            // If this is a distributive conditional type and the check type is generic we need to defer
-            // resolution of the conditional type such that a later instantiation will properly distribute
-            // over union types.
-            const isDeferred = root.isDistributive && maybeTypeOfKind(checkType, TypeFlags.Instantiable);
+            const checkTypeInstantiable = maybeTypeOfKind(checkType, TypeFlags.Instantiable);
             let combinedMapper: TypeMapper | undefined;
             if (root.inferTypeParameters) {
                 const context = createInferenceContext(root.inferTypeParameters, /*signature*/ undefined, InferenceFlags.None);
-                if (!isDeferred) {
+                if (!checkTypeInstantiable) {
                     // We don't want inferences from constraints as they may cause us to eagerly resolve the
                     // conditional type instead of deferring resolution. Also, we always want strict function
                     // types rules (i.e. proper contravariance) for inferences.
                     inferTypes(context.inferences, checkType, extendsType, InferencePriority.NoConstraints | InferencePriority.AlwaysStrict);
                 }
                 combinedMapper = combineTypeMappers(mapper, context);
             }
-            if (!isDeferred) {
-                if (extendsType.flags & TypeFlags.AnyOrUnknown) {
+            // Instantiate the extends type including inferences for 'infer T' type parameters
+            const inferredExtendsType = combinedMapper ? instantiateType(root.extendsType, combinedMapper) : extendsType;
+            // We attempt to resolve the conditional type only when the check and extends types are non-generic
+            if (!checkTypeInstantiable && !maybeTypeOfKind(inferredExtendsType, TypeFlags.Instantiable)) {
+                if (inferredExtendsType.flags & TypeFlags.AnyOrUnknown) {
                     return instantiateType(root.trueType, mapper);
                 }
                 // Return union of trueType and falseType for 'any' since it matches anything
                 if (checkType.flags & TypeFlags.Any) {
                     return getUnionType([instantiateType(root.trueType, combinedMapper || mapper), instantiateType(root.falseType, mapper)]);
                 }
-                // Instantiate the extends type including inferences for 'infer T' type parameters
-                const inferredExtendsType = combinedMapper ? instantiateType(root.extendsType, combinedMapper) : extendsType;
                 // Return falseType for a definitely false extends check. We check an instantations of the two
                 // types with type parameters mapped to the wildcard type, the most permissive instantiations
                 // possible (the wildcard type is assignable to and from all types). If those are not related,

tests/baselines/reference/conditionalTypes2.errors.txt

@@ -212,4 +212,38 @@ tests/cases/conformance/types/conditional/conditionalTypes2.ts(75,12): error TS2
     type T1 = MaybeTrue<{ b: false }>;    // "no"
     type T2 = MaybeTrue<{ b: true }>;     // "yes"
     type T3 = MaybeTrue<{ b: boolean }>;  // "yes"
+    
+    // Repro from #28824
+    
+    type Union = 'a' | 'b';
+    type Product<A extends Union, B> = { f1: A, f2: B};
+    type ProductUnion = Product<'a', 0> | Product<'b', 1>;
+    
+    // {a: "b"; b: "a"}
+    type UnionComplement = {
+      [K in Union]: Exclude<Union, K>
+    };
+    type UCA = UnionComplement['a'];
+    type UCB = UnionComplement['b'];
+    
+    // {a: "a"; b: "b"}
+    type UnionComplementComplement = {
+      [K in Union]: Exclude<Union, Exclude<Union, K>>
+    };
+    type UCCA = UnionComplementComplement['a'];
+    type UCCB = UnionComplementComplement['b'];
+    
+    // {a: Product<'b', 1>; b: Product<'a', 0>}
+    type ProductComplement = {
+      [K in Union]: Exclude<ProductUnion, { f1: K }>
+    };
+    type PCA = ProductComplement['a'];
+    type PCB = ProductComplement['b'];
+    
+    // {a: Product<'a', 0>; b: Product<'b', 1>}
+    type ProductComplementComplement = {
+      [K in Union]: Exclude<ProductUnion, Exclude<ProductUnion, { f1: K }>>
+    };
+    type PCCA = ProductComplementComplement['a'];
+    type PCCB = ProductComplementComplement['b'];
 

tests/baselines/reference/conditionalTypes2.js

@@ -154,6 +154,40 @@ type T0 = MaybeTrue<{ b: never }>     // "no"
 type T1 = MaybeTrue<{ b: false }>;    // "no"
 type T2 = MaybeTrue<{ b: true }>;     // "yes"
 type T3 = MaybeTrue<{ b: boolean }>;  // "yes"
+
+// Repro from #28824
+
+type Union = 'a' | 'b';
+type Product<A extends Union, B> = { f1: A, f2: B};
+type ProductUnion = Product<'a', 0> | Product<'b', 1>;
+
+// {a: "b"; b: "a"}
+type UnionComplement = {
+  [K in Union]: Exclude<Union, K>
+};
+type UCA = UnionComplement['a'];
+type UCB = UnionComplement['b'];
+
+// {a: "a"; b: "b"}
+type UnionComplementComplement = {
+  [K in Union]: Exclude<Union, Exclude<Union, K>>
+};
+type UCCA = UnionComplementComplement['a'];
+type UCCB = UnionComplementComplement['b'];
+
+// {a: Product<'b', 1>; b: Product<'a', 0>}
+type ProductComplement = {
+  [K in Union]: Exclude<ProductUnion, { f1: K }>
+};
+type PCA = ProductComplement['a'];
+type PCB = ProductComplement['b'];
+
+// {a: Product<'a', 0>; b: Product<'b', 1>}
+type ProductComplementComplement = {
+  [K in Union]: Exclude<ProductUnion, Exclude<ProductUnion, { f1: K }>>
+};
+type PCCA = ProductComplementComplement['a'];
+type PCCB = ProductComplementComplement['b'];
 
 
 //// [conditionalTypes2.js]
@@ -328,3 +362,33 @@ declare type T2 = MaybeTrue<{
 declare type T3 = MaybeTrue<{
     b: boolean;
 }>;
+declare type Union = 'a' | 'b';
+declare type Product<A extends Union, B> = {
+    f1: A;
+    f2: B;
+};
+declare type ProductUnion = Product<'a', 0> | Product<'b', 1>;
+declare type UnionComplement = {
+    [K in Union]: Exclude<Union, K>;
+};
+declare type UCA = UnionComplement['a'];
+declare type UCB = UnionComplement['b'];
+declare type UnionComplementComplement = {
+    [K in Union]: Exclude<Union, Exclude<Union, K>>;
+};
+declare type UCCA = UnionComplementComplement['a'];
+declare type UCCB = UnionComplementComplement['b'];
+declare type ProductComplement = {
+    [K in Union]: Exclude<ProductUnion, {
+        f1: K;
+    }>;
+};
+declare type PCA = ProductComplement['a'];
+declare type PCB = ProductComplement['b'];
+declare type ProductComplementComplement = {
+    [K in Union]: Exclude<ProductUnion, Exclude<ProductUnion, {
+        f1: K;
+    }>>;
+};
+declare type PCCA = ProductComplementComplement['a'];
+declare type PCCB = ProductComplementComplement['b'];

tests/baselines/reference/conditionalTypes2.symbols

@@ -579,3 +579,109 @@ type T3 = MaybeTrue<{ b: boolean }>;  // "yes"
 >MaybeTrue : Symbol(MaybeTrue, Decl(conditionalTypes2.ts, 145, 63))
 >b : Symbol(b, Decl(conditionalTypes2.ts, 154, 21))
 
+// Repro from #28824
+
+type Union = 'a' | 'b';
+>Union : Symbol(Union, Decl(conditionalTypes2.ts, 154, 36))
+
+type Product<A extends Union, B> = { f1: A, f2: B};
+>Product : Symbol(Product, Decl(conditionalTypes2.ts, 158, 23))
+>A : Symbol(A, Decl(conditionalTypes2.ts, 159, 13))
+>Union : Symbol(Union, Decl(conditionalTypes2.ts, 154, 36))
+>B : Symbol(B, Decl(conditionalTypes2.ts, 159, 29))
+>f1 : Symbol(f1, Decl(conditionalTypes2.ts, 159, 36))
+>A : Symbol(A, Decl(conditionalTypes2.ts, 159, 13))
+>f2 : Symbol(f2, Decl(conditionalTypes2.ts, 159, 43))
+>B : Symbol(B, Decl(conditionalTypes2.ts, 159, 29))
+
+type ProductUnion = Product<'a', 0> | Product<'b', 1>;
+>ProductUnion : Symbol(ProductUnion, Decl(conditionalTypes2.ts, 159, 51))
+>Product : Symbol(Product, Decl(conditionalTypes2.ts, 158, 23))
+>Product : Symbol(Product, Decl(conditionalTypes2.ts, 158, 23))
+
+// {a: "b"; b: "a"}
+type UnionComplement = {
+>UnionComplement : Symbol(UnionComplement, Decl(conditionalTypes2.ts, 160, 54))
+
+  [K in Union]: Exclude<Union, K>
+>K : Symbol(K, Decl(conditionalTypes2.ts, 164, 3))
+>Union : Symbol(Union, Decl(conditionalTypes2.ts, 154, 36))
+>Exclude : Symbol(Exclude, Decl(lib.es5.d.ts, --, --))
+>Union : Symbol(Union, Decl(conditionalTypes2.ts, 154, 36))
+>K : Symbol(K, Decl(conditionalTypes2.ts, 164, 3))
+
+};
+type UCA = UnionComplement['a'];
+>UCA : Symbol(UCA, Decl(conditionalTypes2.ts, 165, 2))
+>UnionComplement : Symbol(UnionComplement, Decl(conditionalTypes2.ts, 160, 54))
+
+type UCB = UnionComplement['b'];
+>UCB : Symbol(UCB, Decl(conditionalTypes2.ts, 166, 32))
+>UnionComplement : Symbol(UnionComplement, Decl(conditionalTypes2.ts, 160, 54))
+
+// {a: "a"; b: "b"}
+type UnionComplementComplement = {
+>UnionComplementComplement : Symbol(UnionComplementComplement, Decl(conditionalTypes2.ts, 167, 32))
+
+  [K in Union]: Exclude<Union, Exclude<Union, K>>
+>K : Symbol(K, Decl(conditionalTypes2.ts, 171, 3))
+>Union : Symbol(Union, Decl(conditionalTypes2.ts, 154, 36))
+>Exclude : Symbol(Exclude, Decl(lib.es5.d.ts, --, --))
+>Union : Symbol(Union, Decl(conditionalTypes2.ts, 154, 36))
+>Exclude : Symbol(Exclude, Decl(lib.es5.d.ts, --, --))
+>Union : Symbol(Union, Decl(conditionalTypes2.ts, 154, 36))
+>K : Symbol(K, Decl(conditionalTypes2.ts, 171, 3))
+
+};
+type UCCA = UnionComplementComplement['a'];
+>UCCA : Symbol(UCCA, Decl(conditionalTypes2.ts, 172, 2))
+>UnionComplementComplement : Symbol(UnionComplementComplement, Decl(conditionalTypes2.ts, 167, 32))
+
+type UCCB = UnionComplementComplement['b'];
+>UCCB : Symbol(UCCB, Decl(conditionalTypes2.ts, 173, 43))
+>UnionComplementComplement : Symbol(UnionComplementComplement, Decl(conditionalTypes2.ts, 167, 32))
+
+// {a: Product<'b', 1>; b: Product<'a', 0>}
+type ProductComplement = {
+>ProductComplement : Symbol(ProductComplement, Decl(conditionalTypes2.ts, 174, 43))
+
+  [K in Union]: Exclude<ProductUnion, { f1: K }>
+>K : Symbol(K, Decl(conditionalTypes2.ts, 178, 3))
+>Union : Symbol(Union, Decl(conditionalTypes2.ts, 154, 36))
+>Exclude : Symbol(Exclude, Decl(lib.es5.d.ts, --, --))
+>ProductUnion : Symbol(ProductUnion, Decl(conditionalTypes2.ts, 159, 51))
+>f1 : Symbol(f1, Decl(conditionalTypes2.ts, 178, 39))
+>K : Symbol(K, Decl(conditionalTypes2.ts, 178, 3))
+
+};
+type PCA = ProductComplement['a'];
+>PCA : Symbol(PCA, Decl(conditionalTypes2.ts, 179, 2))
+>ProductComplement : Symbol(ProductComplement, Decl(conditionalTypes2.ts, 174, 43))
+
+type PCB = ProductComplement['b'];
+>PCB : Symbol(PCB, Decl(conditionalTypes2.ts, 180, 34))
+>ProductComplement : Symbol(ProductComplement, Decl(conditionalTypes2.ts, 174, 43))
+
+// {a: Product<'a', 0>; b: Product<'b', 1>}
+type ProductComplementComplement = {
+>ProductComplementComplement : Symbol(ProductComplementComplement, Decl(conditionalTypes2.ts, 181, 34))
+
+  [K in Union]: Exclude<ProductUnion, Exclude<ProductUnion, { f1: K }>>
+>K : Symbol(K, Decl(conditionalTypes2.ts, 185, 3))
+>Union : Symbol(Union, Decl(conditionalTypes2.ts, 154, 36))
+>Exclude : Symbol(Exclude, Decl(lib.es5.d.ts, --, --))
+>ProductUnion : Symbol(ProductUnion, Decl(conditionalTypes2.ts, 159, 51))
+>Exclude : Symbol(Exclude, Decl(lib.es5.d.ts, --, --))
+>ProductUnion : Symbol(ProductUnion, Decl(conditionalTypes2.ts, 159, 51))
+>f1 : Symbol(f1, Decl(conditionalTypes2.ts, 185, 61))
+>K : Symbol(K, Decl(conditionalTypes2.ts, 185, 3))
+
+};
+type PCCA = ProductComplementComplement['a'];
+>PCCA : Symbol(PCCA, Decl(conditionalTypes2.ts, 186, 2))
+>ProductComplementComplement : Symbol(ProductComplementComplement, Decl(conditionalTypes2.ts, 181, 34))
+
+type PCCB = ProductComplementComplement['b'];
+>PCCB : Symbol(PCCB, Decl(conditionalTypes2.ts, 187, 45))
+>ProductComplementComplement : Symbol(ProductComplementComplement, Decl(conditionalTypes2.ts, 181, 34))
+

tests/baselines/reference/conditionalTypes2.types

@@ -366,3 +366,68 @@ type T3 = MaybeTrue<{ b: boolean }>;  // "yes"
 >T3 : "yes"
 >b : boolean
 
+// Repro from #28824
+
+type Union = 'a' | 'b';
+>Union : Union
+
+type Product<A extends Union, B> = { f1: A, f2: B};
+>Product : Product<A, B>
+>f1 : A
+>f2 : B
+
+type ProductUnion = Product<'a', 0> | Product<'b', 1>;
+>ProductUnion : ProductUnion
+
+// {a: "b"; b: "a"}
+type UnionComplement = {
+>UnionComplement : UnionComplement
+
+  [K in Union]: Exclude<Union, K>
+};
+type UCA = UnionComplement['a'];
+>UCA : "b"
+
+type UCB = UnionComplement['b'];
+>UCB : "a"
+
+// {a: "a"; b: "b"}
+type UnionComplementComplement = {
+>UnionComplementComplement : UnionComplementComplement
+
+  [K in Union]: Exclude<Union, Exclude<Union, K>>
+};
+type UCCA = UnionComplementComplement['a'];
+>UCCA : "a"
+
+type UCCB = UnionComplementComplement['b'];
+>UCCB : "b"
+
+// {a: Product<'b', 1>; b: Product<'a', 0>}
+type ProductComplement = {
+>ProductComplement : ProductComplement
+
+  [K in Union]: Exclude<ProductUnion, { f1: K }>
+>f1 : K
+
+};
+type PCA = ProductComplement['a'];
+>PCA : Product<"b", 1>
+
+type PCB = ProductComplement['b'];
+>PCB : Product<"a", 0>
+
+// {a: Product<'a', 0>; b: Product<'b', 1>}
+type ProductComplementComplement = {
+>ProductComplementComplement : ProductComplementComplement
+
+  [K in Union]: Exclude<ProductUnion, Exclude<ProductUnion, { f1: K }>>
+>f1 : K
+
+};
+type PCCA = ProductComplementComplement['a'];
+>PCCA : Product<"a", 0>
+
+type PCCB = ProductComplementComplement['b'];
+>PCCB : Product<"b", 1>
+

tests/baselines/reference/infiniteConstraints.types

@@ -15,7 +15,7 @@ type AProp<T extends { a: string }> = T
 >a : string
 
 declare function myBug<
->myBug : <T extends { [K in keyof T]: T[K]; }>(arg: T) => T
+>myBug : <T extends { [K in keyof T]: T[K] extends infer U ? U : never; }>(arg: T) => T
 
   T extends { [K in keyof T]: T[K] extends AProp<infer U> ? U : never }
 >(arg: T): T
@@ -24,7 +24,7 @@ declare function myBug<
 const out = myBug({obj1: {a: "test"}})
 >out : { obj1: { a: string; }; }
 >myBug({obj1: {a: "test"}}) : { obj1: { a: string; }; }
->myBug : <T extends { [K in keyof T]: T[K]; }>(arg: T) => T
+>myBug : <T extends { [K in keyof T]: T[K] extends infer U ? U : never; }>(arg: T) => T
 >{obj1: {a: "test"}} : { obj1: { a: string; }; }
 >obj1 : { a: string; }
 >{a: "test"} : { a: string; }

tests/baselines/reference/unknownType1.types

@@ -76,7 +76,7 @@ type T31<T> = T extends unknown ? true : false;  // Deferred (so it distributes)
 >false : false
 
 type T32<T> = never extends T ? true : false;  // true
->T32 : true
+>T32 : T32<T>
 >true : true
 >false : false
 

tests/cases/conformance/types/conditional/conditionalTypes2.ts

@@ -156,3 +156,37 @@ type T0 = MaybeTrue<{ b: never }>     // "no"
 type T1 = MaybeTrue<{ b: false }>;    // "no"
 type T2 = MaybeTrue<{ b: true }>;     // "yes"
 type T3 = MaybeTrue<{ b: boolean }>;  // "yes"
+
+// Repro from #28824
+
+type Union = 'a' | 'b';
+type Product<A extends Union, B> = { f1: A, f2: B};
+type ProductUnion = Product<'a', 0> | Product<'b', 1>;
+
+// {a: "b"; b: "a"}
+type UnionComplement = {
+  [K in Union]: Exclude<Union, K>
+};
+type UCA = UnionComplement['a'];
+type UCB = UnionComplement['b'];
+
+// {a: "a"; b: "b"}
+type UnionComplementComplement = {
+  [K in Union]: Exclude<Union, Exclude<Union, K>>
+};
+type UCCA = UnionComplementComplement['a'];
+type UCCB = UnionComplementComplement['b'];
+
+// {a: Product<'b', 1>; b: Product<'a', 0>}
+type ProductComplement = {
+  [K in Union]: Exclude<ProductUnion, { f1: K }>
+};
+type PCA = ProductComplement['a'];
+type PCB = ProductComplement['b'];
+
+// {a: Product<'a', 0>; b: Product<'b', 1>}
+type ProductComplementComplement = {
+  [K in Union]: Exclude<ProductUnion, Exclude<ProductUnion, { f1: K }>>
+};
+type PCCA = ProductComplementComplement['a'];
+type PCCB = ProductComplementComplement['b'];