Merge pull request #31116 from Microsoft/higherOrderConstructorTypes

Support higher order inferences for constructor functions

Author: ahejlsberg

src/compiler/checker.ts

@@ -8565,7 +8565,7 @@ namespace ts {
         function getSignatureInstantiation(signature: Signature, typeArguments: Type[] | undefined, isJavascript: boolean, inferredTypeParameters?: ReadonlyArray<TypeParameter>): Signature {
             const instantiatedSignature = getSignatureInstantiationWithoutFillingInTypeArguments(signature, fillMissingTypeArguments(typeArguments, signature.typeParameters, getMinTypeArgumentCount(signature.typeParameters), isJavascript));
             if (inferredTypeParameters) {
-                const returnSignature = getSingleCallSignature(getReturnTypeOfSignature(instantiatedSignature));
+                const returnSignature = getSingleCallOrConstructSignature(getReturnTypeOfSignature(instantiatedSignature));
                 if (returnSignature) {
                     const newReturnSignature = cloneSignature(returnSignature);
                     newReturnSignature.typeParameters = inferredTypeParameters;
@@ -8641,7 +8641,8 @@ namespace ts {
             // object type literal or interface (using the new keyword). Each way of declaring a constructor
             // will result in a different declaration kind.
             if (!signature.isolatedSignatureType) {
-                const isConstructor = signature.declaration!.kind === SyntaxKind.Constructor || signature.declaration!.kind === SyntaxKind.ConstructSignature; // TODO: GH#18217
+                const kind = signature.declaration ? signature.declaration.kind : SyntaxKind.Unknown;
+                const isConstructor = kind === SyntaxKind.Constructor || kind === SyntaxKind.ConstructSignature || kind === SyntaxKind.ConstructorType;
                 const type = createObjectType(ObjectFlags.Anonymous);
                 type.members = emptySymbols;
                 type.properties = emptyArray;
@@ -20630,11 +20631,24 @@ namespace ts {
 
         // If type has a single call signature and no other members, return that signature. Otherwise, return undefined.
         function getSingleCallSignature(type: Type): Signature | undefined {
+            return getSingleSignature(type, SignatureKind.Call, /*allowMembers*/ false);
+        }
+
+        function getSingleCallOrConstructSignature(type: Type): Signature | undefined {
+            return getSingleSignature(type, SignatureKind.Call, /*allowMembers*/ false) ||
+                getSingleSignature(type, SignatureKind.Construct, /*allowMembers*/ false);
+        }
+
+        function getSingleSignature(type: Type, kind: SignatureKind, allowMembers: boolean): Signature | undefined {
             if (type.flags & TypeFlags.Object) {
                 const resolved = resolveStructuredTypeMembers(<ObjectType>type);
-                if (resolved.callSignatures.length === 1 && resolved.constructSignatures.length === 0 &&
-                    resolved.properties.length === 0 && !resolved.stringIndexInfo && !resolved.numberIndexInfo) {
-                    return resolved.callSignatures[0];
+                if (allowMembers || resolved.properties.length === 0 && !resolved.stringIndexInfo && !resolved.numberIndexInfo) {
+                    if (kind === SignatureKind.Call && resolved.callSignatures.length === 1 && resolved.constructSignatures.length === 0) {
+                        return resolved.callSignatures[0];
+                    }
+                    if (kind === SignatureKind.Construct && resolved.constructSignatures.length === 1 && resolved.callSignatures.length === 0) {
+                        return resolved.constructSignatures[0];
+                    }
                 }
             }
             return undefined;
@@ -23976,24 +23990,27 @@ namespace ts {
 
         function instantiateTypeWithSingleGenericCallSignature(node: Expression | MethodDeclaration | QualifiedName, type: Type, checkMode?: CheckMode) {
             if (checkMode && checkMode & (CheckMode.Inferential | CheckMode.SkipGenericFunctions)) {
-                const signature = getSingleCallSignature(type);
+                const callSignature = getSingleSignature(type, SignatureKind.Call, /*allowMembers*/ true);
+                const constructSignature = getSingleSignature(type, SignatureKind.Construct, /*allowMembers*/ true);
+                const signature = callSignature || constructSignature;
                 if (signature && signature.typeParameters) {
-                    if (checkMode & CheckMode.SkipGenericFunctions) {
-                        skippedGenericFunction(node, checkMode);
-                        return anyFunctionType;
-                    }
                     const contextualType = getApparentTypeOfContextualType(<Expression>node);
-                    if (contextualType) {
-                        const contextualSignature = getSingleCallSignature(getNonNullableType(contextualType));
+                    if (contextualType && !isMixinConstructorType(contextualType)) {
+                        const contextualSignature = getSingleSignature(getNonNullableType(contextualType), callSignature ? SignatureKind.Call : SignatureKind.Construct, /*allowMembers*/ false);
                         if (contextualSignature && !contextualSignature.typeParameters) {
+                            if (checkMode & CheckMode.SkipGenericFunctions) {
+                                skippedGenericFunction(node, checkMode);
+                                return anyFunctionType;
+                            }
                             const context = getInferenceContext(node)!;
                             // We have an expression that is an argument of a generic function for which we are performing
                             // type argument inference. The expression is of a function type with a single generic call
                             // signature and a contextual function type with a single non-generic call signature. Now check
                             // if the outer function returns a function type with a single non-generic call signature and
                             // if some of the outer function type parameters have no inferences so far. If so, we can
                             // potentially add inferred type parameters to the outer function return type.
-                            const returnSignature = context.signature && getSingleCallSignature(getReturnTypeOfSignature(context.signature));
+                            const returnType = context.signature && getReturnTypeOfSignature(context.signature);
+                            const returnSignature = returnType && getSingleCallOrConstructSignature(returnType);
                             if (returnSignature && !returnSignature.typeParameters && !every(context.inferences, hasInferenceCandidates)) {
                                 // Instantiate the signature with its own type parameters as type arguments, possibly
                                 // renaming the type parameters to ensure they have unique names.

tests/baselines/reference/genericCallWithFunctionTypedArguments2.types

@@ -78,15 +78,15 @@ var r4 = foo2(1, i2); // error
 >i2 : I2<string>
 
 var r4b = foo2(1, a); // any
->r4b : unknown
->foo2(1, a) : unknown
+>r4b : number
+>foo2(1, a) : number
 >foo2 : <T, U>(x: T, cb: new (a: T) => U) => U
 >1 : 1
 >a : new <T>(x: T) => T
 
 var r5 = foo2(1, i); // any
->r5 : unknown
->foo2(1, i) : unknown
+>r5 : number
+>foo2(1, i) : number
 >foo2 : <T, U>(x: T, cb: new (a: T) => U) => U
 >1 : 1
 >i : I
@@ -112,16 +112,16 @@ function foo3<T, U>(x: T, cb: new(a: T) => U, y: U) {
 }
 
 var r7 = foo3(null, i, ''); // any
->r7 : unknown
->foo3(null, i, '') : unknown
+>r7 : any
+>foo3(null, i, '') : any
 >foo3 : <T, U>(x: T, cb: new (a: T) => U, y: U) => U
 >null : null
 >i : I
 >'' : ""
 
 var r7b = foo3(null, a, ''); // any
->r7b : unknown
->foo3(null, a, '') : unknown
+>r7b : any
+>foo3(null, a, '') : any
 >foo3 : <T, U>(x: T, cb: new (a: T) => U, y: U) => U
 >null : null
 >a : new <T>(x: T) => T

tests/baselines/reference/genericFunctionInference1.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/compiler/genericFunctionInference1.ts(88,14): error TS2345: Argument of type '<a>(value: { key: a; }) => a' is not assignable to parameter of type '(value: Data) => string'.
+tests/cases/compiler/genericFunctionInference1.ts(135,14): 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'.
 
 
@@ -67,6 +67,53 @@ tests/cases/compiler/genericFunctionInference1.ts(88,14): error TS2345: Argument
 
     let f60 = wrap3(baz);
 
+    declare const list2: {
+        <T>(a: T): T[];
+        foo: string;
+        bar(): number;
+    }
+    
+    let f70 = pipe(list2, box);
+    let f71 = pipe(box, list2);
+    
+    declare class Point {
+        constructor(x: number, y: number);
+        readonly x: number;
+        readonly y: number;
+    }
+    
+    declare class Bag<T> {
+        constructor(...args: T[]);
+        contains(value: T): boolean;
+        static foo: string;
+    }
+    
+    function asFunction<A extends any[], B>(cf: new (...args: A) => B) {
+        return (...args: A) => new cf(...args);
+    }
+    
+    const newPoint = asFunction(Point);
+    const newBag = asFunction(Bag);
+    const p1 = new Point(10, 20);
+    const p2 = newPoint(10, 20);
+    const bag1 = new Bag(1, 2, 3);
+    const bag2 = newBag('a', 'b', 'c');
+    
+    declare class Comp<P> {
+        props: P;
+        constructor(props: P);
+    }
+    
+    type CompClass<P> = new (props: P) => Comp<P>;
+    
+    declare function myHoc<P>(C: CompClass<P>): CompClass<P>;
+    
+    type GenericProps<T> = { foo: number, stuff: T };
+    
+    declare class GenericComp<T> extends Comp<GenericProps<T>> {}
+    
+    const GenericComp2 = myHoc(GenericComp);
+    
     // #417
 
     function mirror<A, B>(f: (a: A) => B): (a: A) => B { return f; }

tests/baselines/reference/genericFunctionInference1.js

@@ -63,6 +63,53 @@ declare function baz<T, U extends T>(t1: T, t2: T, u: U): [T, U];
 
 let f60 = wrap3(baz);
 
+declare const list2: {
+    <T>(a: T): T[];
+    foo: string;
+    bar(): number;
+}
+
+let f70 = pipe(list2, box);
+let f71 = pipe(box, list2);
+
+declare class Point {
+    constructor(x: number, y: number);
+    readonly x: number;
+    readonly y: number;
+}
+
+declare class Bag<T> {
+    constructor(...args: T[]);
+    contains(value: T): boolean;
+    static foo: string;
+}
+
+function asFunction<A extends any[], B>(cf: new (...args: A) => B) {
+    return (...args: A) => new cf(...args);
+}
+
+const newPoint = asFunction(Point);
+const newBag = asFunction(Bag);
+const p1 = new Point(10, 20);
+const p2 = newPoint(10, 20);
+const bag1 = new Bag(1, 2, 3);
+const bag2 = newBag('a', 'b', 'c');
+
+declare class Comp<P> {
+    props: P;
+    constructor(props: P);
+}
+
+type CompClass<P> = new (props: P) => Comp<P>;
+
+declare function myHoc<P>(C: CompClass<P>): CompClass<P>;
+
+type GenericProps<T> = { foo: number, stuff: T };
+
+declare class GenericComp<T> extends Comp<GenericProps<T>> {}
+
+const GenericComp2 = myHoc(GenericComp);
+
 // #417
 
 function mirror<A, B>(f: (a: A) => B): (a: A) => B { return f; }
@@ -242,6 +289,18 @@ const f40 = pipe4([list, box]);
 const f41 = pipe4([box, list]);
 const f50 = pipe5(list); // No higher order inference
 let f60 = wrap3(baz);
+let f70 = pipe(list2, box);
+let f71 = pipe(box, list2);
+function asFunction(cf) {
+    return (...args) => new cf(...args);
+}
+const newPoint = asFunction(Point);
+const newBag = asFunction(Bag);
+const p1 = new Point(10, 20);
+const p2 = newPoint(10, 20);
+const bag1 = new Bag(1, 2, 3);
+const bag2 = newBag('a', 'b', 'c');
+const GenericComp2 = myHoc(GenericComp);
 // #417
 function mirror(f) { return f; }
 var identityM = mirror(identity);