Strict bind, call, and apply methods on functions

src/compiler/checker.ts

@@ -77,6 +77,7 @@ namespace ts {
         const allowSyntheticDefaultImports = getAllowSyntheticDefaultImports(compilerOptions);
         const strictNullChecks = getStrictOptionValue(compilerOptions, "strictNullChecks");
         const strictFunctionTypes = getStrictOptionValue(compilerOptions, "strictFunctionTypes");
+        const strictBindCallApply = getStrictOptionValue(compilerOptions, "strictBindCallApply");
         const strictPropertyInitialization = getStrictOptionValue(compilerOptions, "strictPropertyInitialization");
         const noImplicitAny = getStrictOptionValue(compilerOptions, "noImplicitAny");
         const noImplicitThis = getStrictOptionValue(compilerOptions, "noImplicitThis");
@@ -463,6 +464,8 @@ namespace ts {
 
         let globalObjectType: ObjectType;
         let globalFunctionType: ObjectType;
+        let globalCallableFunctionType: ObjectType;
+        let globalNewableFunctionType: ObjectType;
         let globalArrayType: GenericType;
         let globalReadonlyArrayType: GenericType;
         let globalStringType: ObjectType;
@@ -7369,8 +7372,12 @@ namespace ts {
                 if (symbol && symbolIsValue(symbol)) {
                     return symbol;
                 }
-                if (resolved === anyFunctionType || resolved.callSignatures.length || resolved.constructSignatures.length) {
-                    const symbol = getPropertyOfObjectType(globalFunctionType, name);
+                const functionType = resolved === anyFunctionType ? globalFunctionType :
+                    resolved.callSignatures.length ? globalCallableFunctionType :
+                    resolved.constructSignatures.length ? globalNewableFunctionType :
+                    undefined;
+                if (functionType) {
+                    const symbol = getPropertyOfObjectType(functionType, name);
                     if (symbol) {
                         return symbol;
                     }
@@ -13148,10 +13155,8 @@ namespace ts {
             const targetCount = getParameterCount(target);
             const sourceRestType = getEffectiveRestType(source);
             const targetRestType = getEffectiveRestType(target);
-            const paramCount = targetRestType ? Math.min(targetCount - 1, sourceCount) :
-                sourceRestType ? targetCount :
-                Math.min(sourceCount, targetCount);
-
+            const targetNonRestCount = targetRestType ? targetCount - 1 : targetCount;
+            const paramCount = sourceRestType ? targetNonRestCount : Math.min(sourceCount, targetNonRestCount);
             const sourceThisType = getThisTypeOfSignature(source);
             if (sourceThisType) {
                 const targetThisType = getThisTypeOfSignature(target);
@@ -13779,15 +13784,17 @@ namespace ts {
             if (!inferredType) {
                 const signature = context.signature;
                 if (signature) {
-                    if (inference.contraCandidates && (!inference.candidates || inference.candidates.length === 1 && inference.candidates[0].flags & TypeFlags.Never)) {
-                        // If we have contravariant inferences, but no covariant inferences or a single
-                        // covariant inference of 'never', we find the best common subtype and treat that
-                        // as a single covariant candidate.
-                        inference.candidates = [getContravariantInference(inference)];
-                        inference.contraCandidates = undefined;
-                    }
-                    if (inference.candidates) {
-                        inferredType = getCovariantInference(inference, signature);
+                    const inferredCovariantType = inference.candidates ? getCovariantInference(inference, signature) : undefined;
+                    if (inference.contraCandidates) {
+                        const inferredContravariantType = getContravariantInference(inference);
+                        // If we have both co- and contra-variant inferences, we prefer the contra-variant inference
+                        // unless the co-variant inference is a subtype and not 'never'.
+                        inferredType = inferredCovariantType && !(inferredCovariantType.flags & TypeFlags.Never) &&
+                            isTypeSubtypeOf(inferredCovariantType, inferredContravariantType) ?
+                            inferredCovariantType : inferredContravariantType;
+                    }
+                    else if (inferredCovariantType) {
+                        inferredType = inferredCovariantType;
                     }
                     else if (context.flags & InferenceFlags.NoDefault) {
                         // We use silentNeverType as the wildcard that signals no inferences.
@@ -19503,7 +19510,10 @@ namespace ts {
                         checkCandidate = candidate;
                     }
                     if (!checkApplicableSignature(node, args, checkCandidate, relation, excludeArgument, /*reportErrors*/ false)) {
-                        candidateForArgumentError = checkCandidate;
+                        // Give preference to error candidates that have no rest parameters (as they are more specific)
+                        if (!candidateForArgumentError || getEffectiveRestType(candidateForArgumentError) || !getEffectiveRestType(checkCandidate)) {
+                            candidateForArgumentError = checkCandidate;
+                        }
                         continue;
                     }
                     if (excludeArgument) {
@@ -19516,7 +19526,10 @@ namespace ts {
                             checkCandidate = getSignatureInstantiation(candidate, typeArgumentTypes, isInJSFile(candidate.declaration));
                         }
                         if (!checkApplicableSignature(node, args, checkCandidate, relation, excludeArgument, /*reportErrors*/ false)) {
-                            candidateForArgumentError = checkCandidate;
+                            // Give preference to error candidates that have no rest parameters (as they are more specific)
+                            if (!candidateForArgumentError || getEffectiveRestType(candidateForArgumentError) || !getEffectiveRestType(checkCandidate)) {
+                                candidateForArgumentError = checkCandidate;
+                            }
                             continue;
                         }
                     }
@@ -27831,8 +27844,11 @@ namespace ts {
         function getAugmentedPropertiesOfType(type: Type): Symbol[] {
             type = getApparentType(type);
             const propsByName = createSymbolTable(getPropertiesOfType(type));
-            if (typeHasCallOrConstructSignatures(type)) {
-                forEach(getPropertiesOfType(globalFunctionType), p => {
+            const functionType = getSignaturesOfType(type, SignatureKind.Call).length ? globalCallableFunctionType :
+                getSignaturesOfType(type, SignatureKind.Construct).length ? globalNewableFunctionType :
+                undefined;
+            if (functionType) {
+                forEach(getPropertiesOfType(functionType), p => {
                     if (!propsByName.has(p.escapedName)) {
                         propsByName.set(p.escapedName, p);
                     }
@@ -28608,6 +28624,8 @@ namespace ts {
             globalArrayType = getGlobalType("Array" as __String, /*arity*/ 1, /*reportErrors*/ true);
             globalObjectType = getGlobalType("Object" as __String, /*arity*/ 0, /*reportErrors*/ true);
             globalFunctionType = getGlobalType("Function" as __String, /*arity*/ 0, /*reportErrors*/ true);
+            globalCallableFunctionType = strictBindCallApply && getGlobalType("CallableFunction" as __String, /*arity*/ 0, /*reportErrors*/ true) || globalFunctionType;
+            globalNewableFunctionType = strictBindCallApply && getGlobalType("NewableFunction" as __String, /*arity*/ 0, /*reportErrors*/ true) || globalFunctionType;
             globalStringType = getGlobalType("String" as __String, /*arity*/ 0, /*reportErrors*/ true);
             globalNumberType = getGlobalType("Number" as __String, /*arity*/ 0, /*reportErrors*/ true);
             globalBooleanType = getGlobalType("Boolean" as __String, /*arity*/ 0, /*reportErrors*/ true);

src/compiler/commandLineParser.ts

@@ -344,6 +344,14 @@ namespace ts {
             category: Diagnostics.Strict_Type_Checking_Options,
             description: Diagnostics.Enable_strict_checking_of_function_types
         },
+        {
+            name: "strictBindCallApply",
+            type: "boolean",
+            strictFlag: true,
+            showInSimplifiedHelpView: true,
+            category: Diagnostics.Strict_Type_Checking_Options,
+            description: Diagnostics.Enable_strict_bind_call_and_apply_methods_on_functions
+        },
         {
             name: "strictPropertyInitialization",
             type: "boolean",

src/compiler/diagnosticMessages.json

@@ -3752,6 +3752,10 @@
         "category": "Message",
         "code": 6213
     },
+    "Enable strict 'bind', 'call', and 'apply' methods on functions.": {
+        "category": "Message",
+        "code": 6214
+    },
 
     "Projects to reference": {
         "category": "Message",

src/compiler/types.ts

@@ -4402,6 +4402,7 @@ namespace ts {
         sourceRoot?: string;
         strict?: boolean;
         strictFunctionTypes?: boolean;  // Always combine with strict property
+        strictBindCallApply?: boolean;  // Always combine with strict property
         strictNullChecks?: boolean;  // Always combine with strict property
         strictPropertyInitialization?: boolean;  // Always combine with strict property
         stripInternal?: boolean;

src/compiler/utilities.ts

@@ -7094,7 +7094,7 @@ namespace ts {
         return !!(compilerOptions.declaration || compilerOptions.composite);
     }
 
-    export type StrictOptionName = "noImplicitAny" | "noImplicitThis" | "strictNullChecks" | "strictFunctionTypes" | "strictPropertyInitialization" | "alwaysStrict";
+    export type StrictOptionName = "noImplicitAny" | "noImplicitThis" | "strictNullChecks" | "strictFunctionTypes" | "strictBindCallApply" | "strictPropertyInitialization" | "alwaysStrict";
 
     export function getStrictOptionValue(compilerOptions: CompilerOptions, flag: StrictOptionName): boolean {
         return compilerOptions[flag] === undefined ? !!compilerOptions.strict : !!compilerOptions[flag];

src/harness/virtualFileSystemWithWatch.ts

@@ -4,6 +4,8 @@ namespace ts.TestFSWithWatch {
         content: `/// <reference no-default-lib="true"/>
 interface Boolean {}
 interface Function {}
+interface CallableFunction {}
+interface NewableFunction {}
 interface IArguments {}
 interface Number { toExponential: any; }
 interface Object {}

src/lib/es5.d.ts

@@ -295,6 +295,66 @@ interface FunctionConstructor {
 
 declare const Function: FunctionConstructor;
 
+interface CallableFunction extends Function {
+    /**
+      * Calls the function with the specified object as the this value and the elements of specified array as the arguments.
+      * @param thisArg The object to be used as the this object.
+      * @param args An array of argument values to be passed to the function.
+      */
+    apply<T, R>(this: (this: T) => R, thisArg: T): R;
+    apply<T, A extends any[], R>(this: (this: T, ...args: A) => R, thisArg: T, args: A): R;
+
+    /**
+      * Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
+      * @param thisArg The object to be used as the this object.
+      * @param args Argument values to be passed to the function.
+      */
+    call<T, A extends any[], R>(this: (this: T, ...args: A) => R, thisArg: T, ...args: A): R;
+
+    /**
+      * For a given function, creates a bound function that has the same body as the original function.
+      * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
+      * @param thisArg The object to be used as the this object.
+      * @param args Arguments to bind to the parameters of the function.
+      */
+    bind<T, A extends any[], R>(this: (this: T, ...args: A) => R, thisArg: T): (...args: A) => R;
+    bind<T, A0, A extends any[], R>(this: (this: T, arg0: A0, ...args: A) => R, thisArg: T, arg0: A0): (...args: A) => R;
+    bind<T, A0, A1, A extends any[], R>(this: (this: T, arg0: A0, arg1: A1, ...args: A) => R, thisArg: T, arg0: A0, arg1: A1): (...args: A) => R;
+    bind<T, A0, A1, A2, A extends any[], R>(this: (this: T, arg0: A0, arg1: A1, arg2: A2, ...args: A) => R, thisArg: T, arg0: A0, arg1: A1, arg2: A2): (...args: A) => R;
+    bind<T, A0, A1, A2, A3, A extends any[], R>(this: (this: T, arg0: A0, arg1: A1, arg2: A2, arg3: A3, ...args: A) => R, thisArg: T, arg0: A0, arg1: A1, arg2: A2, arg3: A3): (...args: A) => R;
+    bind<T, AX, R>(this: (this: T, ...args: AX[]) => R, thisArg: T, ...args: AX[]): (...args: AX[]) => R;
+}
+
+interface NewableFunction extends Function {
+    /**
+      * Calls the function with the specified object as the this value and the elements of specified array as the arguments.
+      * @param thisArg The object to be used as the this object.
+      * @param args An array of argument values to be passed to the function.
+      */
+    apply<T>(this: new () => T, thisArg: T): void;
+    apply<T, A extends any[]>(this: new (...args: A) => T, thisArg: T, args: A): void;
+
+    /**
+      * Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
+      * @param thisArg The object to be used as the this object.
+      * @param args Argument values to be passed to the function.
+      */
+    call<T, A extends any[]>(this: new (...args: A) => T, thisArg: T, ...args: A): void;
+
+    /**
+      * For a given function, creates a bound function that has the same body as the original function.
+      * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
+      * @param thisArg The object to be used as the this object.
+      * @param args Arguments to bind to the parameters of the function.
+      */
+    bind<A extends any[], R>(this: new (...args: A) => R, thisArg: any): new (...args: A) => R;
+    bind<A0, A extends any[], R>(this: new (arg0: A0, ...args: A) => R, thisArg: any, arg0: A0): new (...args: A) => R;
+    bind<A0, A1, A extends any[], R>(this: new (arg0: A0, arg1: A1, ...args: A) => R, thisArg: any, arg0: A0, arg1: A1): new (...args: A) => R;
+    bind<A0, A1, A2, A extends any[], R>(this: new (arg0: A0, arg1: A1, arg2: A2, ...args: A) => R, thisArg: any, arg0: A0, arg1: A1, arg2: A2): new (...args: A) => R;
+    bind<A0, A1, A2, A3, A extends any[], R>(this: new (arg0: A0, arg1: A1, arg2: A2, arg3: A3, ...args: A) => R, thisArg: any, arg0: A0, arg1: A1, arg2: A2, arg3: A3): new (...args: A) => R;
+    bind<AX, R>(this: new (...args: AX[]) => R, thisArg: any, ...args: AX[]): new (...args: AX[]) => R;
+}
+
 interface IArguments {
     [index: number]: any;
     length: number;

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2493,6 +2493,7 @@ declare namespace ts {
         sourceRoot?: string;
         strict?: boolean;
         strictFunctionTypes?: boolean;
+        strictBindCallApply?: boolean;
         strictNullChecks?: boolean;
         strictPropertyInitialization?: boolean;
         stripInternal?: boolean;

tests/baselines/reference/api/typescript.d.ts

@@ -2493,6 +2493,7 @@ declare namespace ts {
         sourceRoot?: string;
         strict?: boolean;
         strictFunctionTypes?: boolean;
+        strictBindCallApply?: boolean;
         strictNullChecks?: boolean;
         strictPropertyInitialization?: boolean;
         stripInternal?: boolean;

tests/baselines/reference/booleanLiteralsContextuallyTypedFromUnion.errors.txt

@@ -0,0 +1,31 @@
+error TS2318: Cannot find global type 'CallableFunction'.
+error TS2318: Cannot find global type 'NewableFunction'.
+
+
+!!! error TS2318: Cannot find global type 'CallableFunction'.
+!!! error TS2318: Cannot find global type 'NewableFunction'.
+==== tests/cases/compiler/booleanLiteralsContextuallyTypedFromUnion.tsx (0 errors) ====
+    interface A { isIt: true; text: string; }
+    interface B { isIt: false; value: number; }
+    type C = A | B;
+    const isIt = Math.random() > 0.5;
+    const c: C = isIt ? { isIt, text: 'hey' } : { isIt, value: 123 };
+    const cc: C = isIt ? { isIt: isIt, text: 'hey' } : { isIt: isIt, value: 123 };
+
+    type ComponentProps =
+        | {
+            optionalBool: true;
+            mandatoryFn: () => void;
+        }
+        | {
+            optionalBool: false;
+        };
+
+    let Funk = (_props: ComponentProps) => <div>Hello</div>;
+
+    let Fail1 = () => <Funk mandatoryFn={() => { }} optionalBool={true} />
+    let Fail2 = () => <Funk mandatoryFn={() => { }} optionalBool={true as true} />
+    let True = true as true;
+    let Fail3 = () => <Funk mandatoryFn={() => { }} optionalBool={True} />
+    let attrs2 = { optionalBool: true as true, mandatoryFn: () => { } }
+    let Success = () => <Funk {...attrs2} />

tests/baselines/reference/destructuringParameterDeclaration4.errors.txt

@@ -43,7 +43,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration4.ts(
     a1(...array2);            // Error parameter type is (number|string)[]
           ~~~~~~
 !!! error TS2552: Cannot find name 'array2'. Did you mean 'Array'?
-!!! related TS2728 /.ts/lib.es5.d.ts:1298:15: 'Array' is declared here.
+!!! related TS2728 /.ts/lib.es5.d.ts:1358:15: 'Array' is declared here.
     a5([1, 2, "string", false, true]);       // Error, parameter type is [any, any, [[any]]]
               ~~~~~~~~
 !!! error TS2322: Type 'string' is not assignable to type '[[any]]'.

tests/baselines/reference/externModule.errors.txt

@@ -69,20 +69,20 @@ tests/cases/compiler/externModule.ts(37,3): error TS2552: Cannot find name 'XDat
     var d=new XDate();
               ~~~~~
 !!! error TS2552: Cannot find name 'XDate'. Did you mean 'Date'?
-!!! related TS2728 /.ts/lib.es5.d.ts:837:15: 'Date' is declared here.
+!!! related TS2728 /.ts/lib.es5.d.ts:897:15: 'Date' is declared here.
     d.getDay();
     d=new XDate(1978,2);
           ~~~~~
 !!! error TS2552: Cannot find name 'XDate'. Did you mean 'Date'?
-!!! related TS2728 /.ts/lib.es5.d.ts:837:15: 'Date' is declared here.
+!!! related TS2728 /.ts/lib.es5.d.ts:897:15: 'Date' is declared here.
     d.getXDate();
     var n=XDate.parse("3/2/2004");
           ~~~~~
 !!! error TS2552: Cannot find name 'XDate'. Did you mean 'Date'?
-!!! related TS2728 /.ts/lib.es5.d.ts:837:15: 'Date' is declared here.
+!!! related TS2728 /.ts/lib.es5.d.ts:897:15: 'Date' is declared here.
     n=XDate.UTC(1964,2,1);
       ~~~~~
 !!! error TS2552: Cannot find name 'XDate'. Did you mean 'Date'?
-!!! related TS2728 /.ts/lib.es5.d.ts:837:15: 'Date' is declared here.
+!!! related TS2728 /.ts/lib.es5.d.ts:897:15: 'Date' is declared here.