Merge pull request #30215 from Microsoft/higherOrderFunctionTypeInference

Higher order function type inference

Author: ahejlsberg

Diff for: src/compiler/checker.ts

@@ -4362,6 +4362,7 @@ namespace ts {
         NoDefault       = 1 << 0,  // Infer unknownType for no inferences (otherwise anyType or emptyObjectType)
         AnyDefault      = 1 << 1,  // Infer anyType for no inferences (otherwise emptyObjectType)
         NoFixing        = 1 << 2,  // Disable type parameter fixing
+        SkippedGenericFunction = 1 << 3,
     }
 
     /**
@@ -4391,6 +4392,7 @@ namespace ts {
         flags: InferenceFlags;                        // Inference flags
         compareTypes: TypeComparer;                   // Type comparer function
         returnMapper?: TypeMapper;                    // Type mapper for inferences from return types (if any)
+        inferredTypeParameters?: ReadonlyArray<TypeParameter>;
     }
 
     /* @internal */

Diff for: src/compiler/types.ts

@@ -1798,7 +1798,7 @@ namespace ts {
             const span = createTextSpanFromBounds(start, end);
             const formatContext = formatting.getFormatContext(formatOptions);
 
-            return flatMap(deduplicate(errorCodes, equateValues, compareValues), errorCode => {
+            return flatMap(deduplicate<number>(errorCodes, equateValues, compareValues), errorCode => {
                 cancellationToken.throwIfCancellationRequested();
                 return codefix.getFixes({ errorCode, sourceFile, span, program, host, cancellationToken, formatContext, preferences });
             });

Diff for: src/services/services.ts

@@ -15,8 +15,8 @@ var e = <K>(x: string, y?: K) => x.length;
 >length : number
 
 var r99 = map(e); // should be {}[] for S since a generic lambda is not inferentially typed
->r99 : (a: {}[]) => number[]
->map(e) : (a: {}[]) => number[]
+>r99 : <K>(a: string[]) => number[]
+>map(e) : <K>(a: string[]) => number[]
 >map : <S, T>(f: (x: S) => T) => (a: S[]) => T[]
 >e : <K>(x: string, y?: K) => number
 
@@ -37,8 +37,8 @@ var e2 = <K>(x: string, y?: K) => x.length;
 >length : number
 
 var r100 = map2(e2); // type arg inference should fail for S since a generic lambda is not inferentially typed. Falls back to { length: number }
->r100 : (a: { length: number; }[]) => number[]
->map2(e2) : (a: { length: number; }[]) => number[]
+>r100 : <K>(a: string[]) => number[]
+>map2(e2) : <K>(a: string[]) => number[]
 >map2 : <S extends { length: number; }, T>(f: (x: S) => T) => (a: S[]) => T[]
 >e2 : <K>(x: string, y?: K) => number
 

Diff for: tests/baselines/reference/contextualSignatureInstantiation1.types

@@ -31,8 +31,8 @@ var id: <T>(x:T) => T;
 >x : T
 
 var r23 = dot(id)(id);
->r23 : (_: {}) => {}
->dot(id)(id) : (_: {}) => {}
+>r23 : <T>(_: T) => {}
+>dot(id)(id) : <T>(_: T) => {}
 >dot(id) : <U>(g: (_: U) => {}) => (_: U) => {}
 >dot : <T, S>(f: (_: T) => S) => <U>(g: (_: U) => T) => (_: U) => S
 >id : <T>(x: T) => T

Diff for: tests/baselines/reference/contextualSignatureInstantiation2.types

@@ -0,0 +1,193 @@
+tests/cases/compiler/genericFunctionInference1.ts(83,14): error TS2345: Argument of type '<a>(value: { key: a; }) => a' is not assignable to parameter of type '(value: Data) => string'.
+  Type 'number' is not assignable to type 'string'.
+
+
+==== tests/cases/compiler/genericFunctionInference1.ts (1 errors) ====
+    declare function pipe<A extends any[], B>(ab: (...args: A) => B): (...args: A) => B;
+    declare function pipe<A extends any[], B, C>(ab: (...args: A) => B, bc: (b: B) => C): (...args: A) => C;
+    declare function pipe<A extends any[], B, C, D>(ab: (...args: A) => B, bc: (b: B) => C, cd: (c: C) => D): (...args: A) => D;
+    
+    declare function list<T>(a: T): T[];
+    declare function box<V>(x: V): { value: V };
+    declare function foo<T extends { value: T }>(x: T): T;
+    
+    const f00 = pipe(list);
+    const f01 = pipe(list, box);
+    const f02 = pipe(box, list);
+    const f03 = pipe(x => list(x), box);
+    const f04 = pipe(list, x => box(x));
+    const f05 = pipe(x => list(x), x => box(x))
+    const f06 = pipe(list, pipe(box));
+    const f07 = pipe(x => list(x), pipe(box));
+    const f08 = pipe(x => list(x), pipe(x => box(x)));
+    const f09 = pipe(list, x => x.length);
+    const f10 = pipe(foo);
+    const f11 = pipe(foo, foo);
+    
+    const g00: <T>(x: T) => T[] = pipe(list);
+    const g01: <T>(x: T) => { value: T[] } = pipe(list, box);
+    const g02: <T>(x: T) => { value: T }[] = pipe(box, list);
+    const g03: <T>(x: T) => { value: T[] } = pipe(x => list(x), box);
+    const g04: <T>(x: T) => { value: T[] } = pipe(list, x => box(x));
+    const g05: <T>(x: T) => { value: T[] } = pipe(x => list(x), x => box(x))
+    const g06: <T>(x: T) => { value: T[] } = pipe(list, pipe(box));
+    const g07: <T>(x: T) => { value: T[] } = pipe(x => list(x), pipe(box));
+    const g08: <T>(x: T) => { value: T[] } = pipe(x => list(x), pipe(x => box(x)));
+    const g09: <T>(x: T) => number = pipe(list, x => x.length);
+    const g10: <T extends { value: T }>(x: T) => T = pipe(foo);
+    const g12: <T extends { value: T }>(x: T) => T = pipe(foo, foo);
+    
+    declare function pipe2<A, B, C, D>(ab: (a: A) => B, cd: (c: C) => D): (a: [A, C]) => [B, D];
+    
+    const f20 = pipe2(list, box);
+    const f21 = pipe2(box, list);
+    const f22 = pipe2(list, list);
+    const f23 = pipe2(box, box);
+    const f24 = pipe2(f20, f20);
+    const f25 = pipe2(foo, foo);
+    const f26 = pipe2(f25, f25);
+    
+    declare function pipe3<A, B, C>(ab: (a: A) => B, ac: (a: A) => C): (a: A) => [B, C];
+    
+    const f30 = pipe3(list, box);
+    const f31 = pipe3(box, list);
+    const f32 = pipe3(list, list);
+    
+    declare function pipe4<A, B, C>(funcs: [(a: A) => B, (b: B) => C]): (a: A) => C;
+    
+    const f40 = pipe4([list, box]);
+    const f41 = pipe4([box, list]);
+    
+    declare function pipe5<A, B>(f: (a: A) => B): { f: (a: A) => B };
+    
+    const f50 = pipe5(list);  // No higher order inference
+    
+    // #417
+    
+    function mirror<A, B>(f: (a: A) => B): (a: A) => B { return f; }
+    var identityM = mirror(identity);
+    
+    var x = 1;
+    var y = identity(x);
+    var z = identityM(x);
+    
+    // #3038
+    
+    export function keyOf<a>(value: { key: a; }): a {
+        return value.key;
+    }
+    export interface Data {
+        key: number;
+        value: Date;
+    }
+    
+    var data: Data[] = [];
+    
+    declare function toKeys<a>(values: a[], toKey: (value: a) => string): string[];
+    
+    toKeys(data, keyOf);  // Error
+                 ~~~~~
+!!! error TS2345: Argument of type '<a>(value: { key: a; }) => a' is not assignable to parameter of type '(value: Data) => string'.
+!!! error TS2345:   Type 'number' is not assignable to type 'string'.
+    
+    // #9366
+    
+    function flip<a, b, c>(f: (a: a, b: b) => c): (b: b, a: a) => c {
+      return (b: b, a: a) => f(a, b);
+    }
+    function zip<T, U>(x: T, y: U): [T, U] {
+      return [x, y];
+    }
+    
+    var expected: <T, U>(y: U, x: T) => [T, U] = flip(zip);
+    var actual = flip(zip);
+    
+    // #9366
+    
+    const map = <T, U>(transform: (t: T) => U) =>
+        (arr: T[]) => arr.map(transform)
+    
+    const identityStr = (t: string) => t;
+    
+    const arr: string[] = map(identityStr)(['a']);
+    const arr1: string[] = map(identity)(['a']);
+    
+    // #9949
+    
+    function of2<a, b>(one: a, two: b): [a, b] {
+        return [one, two];
+    }
+    
+    const flipped = flip(of2);
+    
+    // #29904.1
+    
+    type Component<P> = (props: P) => {};
+    
+    declare const myHoc1: <P>(C: Component<P>) => Component<P>;
+    declare const myHoc2: <P>(C: Component<P>) => Component<P>;
+    
+    declare const MyComponent1: Component<{ foo: 1 }>;
+    
+    const enhance = pipe(
+        myHoc1,
+        myHoc2,
+    );
+    
+    const MyComponent2 = enhance(MyComponent1);
+    
+    // #29904.2
+    
+    const fn20 = pipe((_a?: {}) => 1);
+    
+    // #29904.3
+    
+    type Fn = (n: number) => number;
+    const fn30: Fn = pipe(
+        x => x + 1,
+        x => x * 2,
+    );
+    
+    const promise = Promise.resolve(1);
+    promise.then(
+        pipe(
+            x => x + 1,
+            x => x * 2,
+        ),
+    );
+    
+    // #29904.4
+    
+    declare const getString: () => string;
+    declare const orUndefined: (name: string) => string | undefined;
+    declare const identity: <T>(value: T) => T;
+    
+    const fn40 = pipe(
+        getString,
+        string => orUndefined(string),
+        identity,
+    );
+    
+    // #29904.6
+    
+    declare const getArray: () => string[];
+    declare const first: <T>(ts: T[]) => T;
+    
+    const fn60 = pipe(
+        getArray,
+        x => x,
+        first,
+    );
+    
+    const fn61 = pipe(
+        getArray,
+        identity,
+        first,
+    );
+    
+    const fn62 = pipe(
+        getArray,
+        x => x,
+        x => first(x),
+    );
+