Contextually type complex signatures, rather than giving up

src/compiler/checker.ts

@@ -13392,6 +13392,97 @@ namespace ts {
                 getApparentTypeOfContextualType(node);
         }
 
+        function combineSignatures(signatureList: Signature[]): Signature {
+            // Produce a synthetic signature whose arguments are a union of the parameters of the inferred signatures and whose return type is an intersection
+            let parameters: Symbol[];
+            let minimumParameterCount = Number.POSITIVE_INFINITY;
+            let maximumRealParameterCount = 0;
+            let restTypes: Type[];
+            let thisTypes: Type[];
+            let hasLiteralTypes = false;
+
+            // First, collect aggrgate statistics about all signatures to determine the characteristics of the resulting signature
+            for (const signature of signatureList) {
+                if (signature.minArgumentCount < minimumParameterCount) {
+                    minimumParameterCount = signature.minArgumentCount;
+                }
+                if (signature.hasRestParameter) {
+                    (restTypes || (restTypes = [])).push(getRestTypeOfSignature(signature));
+                }
+                if (signature.hasLiteralTypes) {
+                    hasLiteralTypes = true;
+                }
+                const realParameterCount = length(signature.parameters) - (signature.hasRestParameter ? 1 : 0);
+                if (maximumRealParameterCount < realParameterCount) {
+                    maximumRealParameterCount = realParameterCount;
+                }
+                if (signature.thisParameter) {
+                    (thisTypes || (thisTypes = [])).push(getTypeOfSymbol(signature.thisParameter));
+                }
+            }
+
+            // Then, for every real parameter up to the maximum, combine those parameter types and names into a new symbol
+            for (let i = 0; i < maximumRealParameterCount; i++) {
+                const parameterNames: __String[] = [];
+                const parameterTypes: Type[] = [];
+                for (const signature of signatureList) {
+                    let type: Type;
+                    const index = signature.thisParameter ? i + 1 : i;
+                    if (index < (signature.hasRestParameter ? signature.parameters.length - 1 : signature.parameters.length)) {
+                        // If the argument is present, add it to the mixed argument
+                        const param = signature.parameters[index];
+                        if (!contains(parameterNames, param.escapedName)) {
+                            parameterNames.push(param.escapedName);
+                        }
+                        type = getTypeOfSymbol(param);
+                    }
+                    else if (signature.hasRestParameter) {
+                        // Otherwise, if there is a rest type for this signature, add that type
+                        type = getRestTypeOfSignature(signature);
+                    }
+                    else {
+                        // Otherwise, this argument may be `undefined` on some uses
+                        type = undefinedType;
+                    }
+                    if (!contains(parameterTypes, type)) {
+                        parameterTypes.push(type);
+                    }
+                }
+                // We do this so the name is reasonable for users
+                const paramName = escapeLeadingUnderscores(map(parameterNames, unescapeLeadingUnderscores).join("or"));
+                const paramSymbol = createSymbol(SymbolFlags.FunctionScopedVariable, paramName);
+                paramSymbol.type = getUnionType(parameterTypes);
+                (parameters || (parameters = [])).push(paramSymbol);
+            }
+
+            const hasRestParameter = !!(restTypes && restTypes.length);
+            if (hasRestParameter) {
+                const restSymbol = createSymbol(SymbolFlags.FunctionScopedVariable, "rest" as __String);
+                restSymbol.type = getUnionType(restTypes);
+                restSymbol.isRestParameter = true;
+                (parameters || (parameters = [])).push(restSymbol);
+            }
+
+            let thisParameterSymbol: TransientSymbol;
+            if (thisTypes && thisTypes.length) {
+                thisParameterSymbol = createSymbol(SymbolFlags.FunctionScopedVariable, "this" as __String);
+                thisParameterSymbol.type = getUnionType(thisTypes);
+            }
+
+            // TODO (weswigham): Merge type predicates?
+            return createSignature(
+                /*declaration*/ undefined,
+                map(flatMap(signatureList, s => s.typeParameters), cloneTypeParameter),
+                thisParameterSymbol,
+                parameters,
+                getIntersectionType(map(signatureList, getReturnTypeOfSignature)),
+                /*typePredicate*/ undefined,
+                minimumParameterCount,
+                hasRestParameter,
+                hasLiteralTypes
+            );
+        }
+
         // Return the contextual signature for a given expression node. A contextual type provides a
         // contextual signature if it has a single call signature and if that call signature is non-generic.
         // If the contextual type is a union type, get the signature from each type possible and if they are
@@ -13408,6 +13499,7 @@ namespace ts {
             }
             let signatureList: Signature[];
             const types = (<UnionType>type).types;
+            let mismatchedSignatures = false;
             for (const current of types) {
                 const signature = getContextualCallSignature(current, node);
                 if (signature) {
@@ -13416,8 +13508,9 @@ namespace ts {
                         signatureList = [signature];
                     }
                     else if (!compareSignaturesIdentical(signatureList[0], signature, /*partialMatch*/ false, /*ignoreThisTypes*/ true, /*ignoreReturnTypes*/ true, compareTypesIdentical)) {
-                        // Signatures aren't identical, do not use
-                        return undefined;
+                        // Signatures aren't identical, set flag to union parameter types, intersect return types
+                        signatureList.push(signature);
+                        mismatchedSignatures = true;
                     }
                     else {
                         // Use this signature for contextual union signature
@@ -13426,6 +13519,10 @@ namespace ts {
                 }
             }
 
+            if (mismatchedSignatures) {
+                return combineSignatures(signatureList);
+            }
+
             // Result is union of signatures collected (return type is union of return types of this signature set)
             let result: Signature;
             if (signatureList) {

tests/baselines/reference/contextualTypeWithUnionTypeCallSignatures.symbols

@@ -74,7 +74,9 @@ var x3: IWithCallSignatures | IWithCallSignatures3 = a => /*here a should be any
 >IWithCallSignatures : Symbol(IWithCallSignatures, Decl(contextualTypeWithUnionTypeCallSignatures.ts, 9, 1))
 >IWithCallSignatures3 : Symbol(IWithCallSignatures3, Decl(contextualTypeWithUnionTypeCallSignatures.ts, 15, 1))
 >a : Symbol(a, Decl(contextualTypeWithUnionTypeCallSignatures.ts, 32, 52))
+>a.toString : Symbol(toString, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >a : Symbol(a, Decl(contextualTypeWithUnionTypeCallSignatures.ts, 32, 52))
+>toString : Symbol(toString, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 
 // With call signature count mismatch
 var x4: IWithCallSignatures | IWithCallSignatures4 = a => /*here a should be any*/ a.toString();

tests/baselines/reference/contextualTypeWithUnionTypeCallSignatures.types

@@ -78,12 +78,12 @@ var x3: IWithCallSignatures | IWithCallSignatures3 = a => /*here a should be any
 >x3 : IWithCallSignatures | IWithCallSignatures3
 >IWithCallSignatures : IWithCallSignatures
 >IWithCallSignatures3 : IWithCallSignatures3
->a => /*here a should be any*/ a.toString() : (a: any) => any
->a : any
->a.toString() : any
->a.toString : any
->a : any
->toString : any
+>a => /*here a should be any*/ a.toString() : (a: string | number) => string
+>a : string | number
+>a.toString() : string
+>a.toString : ((radix?: number) => string) | (() => string)
+>a : string | number
+>toString : ((radix?: number) => string) | (() => string)
 
 // With call signature count mismatch
 var x4: IWithCallSignatures | IWithCallSignatures4 = a => /*here a should be any*/ a.toString();

tests/baselines/reference/functionExpressionContextualTyping1.errors.txt

@@ -0,0 +1,80 @@
+tests/cases/conformance/expressions/contextualTyping/functionExpressionContextualTyping1.ts(43,17): error TS2339: Property 'toLowerCase' does not exist on type 'string | number'.
+  Property 'toLowerCase' does not exist on type 'number'.
+tests/cases/conformance/expressions/contextualTyping/functionExpressionContextualTyping1.ts(45,7): error TS2339: Property 'toExponential' does not exist on type 'string | number'.
+  Property 'toExponential' does not exist on type 'string'.
+tests/cases/conformance/expressions/contextualTyping/functionExpressionContextualTyping1.ts(52,13): error TS2322: Type '(j: number | T, k: U) => (number | T | U)[]' is not assignable to type '((j: T, k: U) => (T | U)[]) | ((j: number, k: U) => number[])'.
+  Type '(j: number | T, k: U) => (number | T | U)[]' is not assignable to type '(j: number, k: U) => number[]'.
+    Type '(number | T | U)[]' is not assignable to type 'number[]'.
+      Type 'number | T | U' is not assignable to type 'number'.
+        Type 'T' is not assignable to type 'number'.
+
+
+==== tests/cases/conformance/expressions/contextualTyping/functionExpressionContextualTyping1.ts (3 errors) ====
+    // When a function expression with no type parameters and no parameter type annotations 
+    // is contextually typed (section 4.19) by a type T and a contextual signature S can be extracted from T
+
+    enum E { red, blue }
+
+    // A contextual signature S is extracted from a function type T as follows:
+    //      If T is a function type with exactly one call signature, and if that call signature is non- generic, S is that signature.
+
+    var a0: (n: number, s: string) => number = (num, str) => {
+        num.toExponential();
+        return 0;
+    }
+
+    class Class<T> {
+        foo() { }
+    }
+
+    var a1: (c: Class<Number>) => number = (a1) => {
+        a1.foo();
+        return 1;
+    }
+
+    // A contextual signature S is extracted from a function type T as follows:
+    //      If T is a union type, let U be the set of element types in T that have call signatures.
+    //        If each type in U has exactly one call signature and that call signature is non- generic,
+    //        and if all of the signatures are identical ignoring return types,
+    //        then S is a signature with the same parameters and a union of the return types.
+    var b1: ((s: string, w: boolean) => void) | ((s: string, w: boolean) => string);
+    b1 = (k, h) => { };
+    var b2: typeof a0 | ((n: number, s: string) => string);
+    b2 = (foo, bar) => { return foo + 1; }
+    b2 = (foo, bar) => { return "hello"; }
+    var b3: (name: string, num: number, boo: boolean) => void;
+    b3 = (name, number) => { };
+
+    var b4: (n: E) => string = (number = 1) => { return "hello"; };
+    var b5: (n: {}) => string = (number = "string") => { return "hello"; };
+
+    // A contextual signature S is extracted from a function type T as follows:
+    //      Otherwise, no contextual signature can be extracted from T and S is undefined.
+    var b6: ((s: string, w: boolean) => void) | ((n: number) => number);
+    var b7: ((s: string, w: boolean) => void) | ((s: string, w: number) => string);
+    b6 = (k) => { k.toLowerCase() };
+                    ~~~~~~~~~~~
+!!! error TS2339: Property 'toLowerCase' does not exist on type 'string | number'.
+!!! error TS2339:   Property 'toLowerCase' does not exist on type 'number'.
+    b6 = (i) => {
+        i.toExponential();
+          ~~~~~~~~~~~~~
+!!! error TS2339: Property 'toExponential' does not exist on type 'string | number'.
+!!! error TS2339:   Property 'toExponential' does not exist on type 'string'.
+        return i;
+    };                   // Per spec, no contextual signature can be extracted in this case. (Otherwise clause)
+    b7 = (j, m) => { };  // Per spec, no contextual signature can be extracted in this case. (Otherwise clause)
+
+    class C<T, U> {
+        constructor() {
+            var k: ((j: T, k: U) => (T|U)[]) | ((j: number,k :U) => number[]) = (j, k) => {
+                ~
+!!! error TS2322: Type '(j: number | T, k: U) => (number | T | U)[]' is not assignable to type '((j: T, k: U) => (T | U)[]) | ((j: number, k: U) => number[])'.
+!!! error TS2322:   Type '(j: number | T, k: U) => (number | T | U)[]' is not assignable to type '(j: number, k: U) => number[]'.
+!!! error TS2322:     Type '(number | T | U)[]' is not assignable to type 'number[]'.
+!!! error TS2322:       Type 'number | T | U' is not assignable to type 'number'.
+!!! error TS2322:         Type 'T' is not assignable to type 'number'.
+                return [j, k];
+            }   // Per spec, no contextual signature can be extracted in this case.
+        }
+    }