Treat {} in T = {} as any in JS files (#19977)

src/compiler/checker.ts

@@ -6454,7 +6454,10 @@ namespace ts {
                     }
                     for (let i = numTypeArguments; i < numTypeParameters; i++) {
                         const mapper = createTypeMapper(typeParameters, typeArguments);
-                        const defaultType = getDefaultFromTypeParameter(typeParameters[i]);
+                        let defaultType = getDefaultFromTypeParameter(typeParameters[i]);
+                        if (defaultType && isTypeIdenticalTo(defaultType, emptyObjectType) && isJavaScriptImplicitAny) {
+                            defaultType = anyType;
+                        }
                         typeArguments[i] = defaultType ? instantiateType(defaultType, mapper) : getDefaultTypeArgumentType(isJavaScriptImplicitAny);
                     }
                 }

tests/baselines/reference/defaultPropsEmptyCurlyBecomesAnyForJs.js

@@ -0,0 +1,76 @@
+//// [tests/cases/compiler/defaultPropsEmptyCurlyBecomesAnyForJs.ts] ////
+
+//// [library.d.ts]
+export class Foo<T = {}, U = {}> {
+    props: T;
+    state: U;
+    constructor(props: T, state: U);
+}
+
+//// [component.js]
+import { Foo } from "./library";
+export class MyFoo extends Foo {
+    member;
+}
+
+//// [typed_component.ts]
+import { MyFoo } from "./component";
+export class TypedFoo extends MyFoo {
+    constructor() {
+        super({x: "string", y: 42}, { value: undefined });
+        this.props.x;
+        this.props.y;
+        this.state.value;
+        this.member;
+    }
+}
+
+//// [component.js]
+"use strict";
+var __extends = (this && this.__extends) || (function () {
+    var extendStatics = Object.setPrototypeOf ||
+        ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
+        function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
+    return function (d, b) {
+        extendStatics(d, b);
+        function __() { this.constructor = d; }
+        d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
+    };
+})();
+exports.__esModule = true;
+var library_1 = require("./library");
+var MyFoo = /** @class */ (function (_super) {
+    __extends(MyFoo, _super);
+    function MyFoo() {
+        return _super !== null && _super.apply(this, arguments) || this;
+    }
+    return MyFoo;
+}(library_1.Foo));
+exports.MyFoo = MyFoo;
+//// [typed_component.js]
+"use strict";
+var __extends = (this && this.__extends) || (function () {
+    var extendStatics = Object.setPrototypeOf ||
+        ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
+        function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
+    return function (d, b) {
+        extendStatics(d, b);
+        function __() { this.constructor = d; }
+        d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
+    };
+})();
+exports.__esModule = true;
+var component_1 = require("./component");
+var TypedFoo = /** @class */ (function (_super) {
+    __extends(TypedFoo, _super);
+    function TypedFoo() {
+        var _this = _super.call(this, { x: "string", y: 42 }, { value: undefined }) || this;
+        _this.props.x;
+        _this.props.y;
+        _this.state.value;
+        _this.member;
+        return _this;
+    }
+    return TypedFoo;
+}(component_1.MyFoo));
+exports.TypedFoo = TypedFoo;

tests/baselines/reference/defaultPropsEmptyCurlyBecomesAnyForJs.symbols

@@ -0,0 +1,70 @@
+=== tests/cases/compiler/library.d.ts ===
+export class Foo<T = {}, U = {}> {
+>Foo : Symbol(Foo, Decl(library.d.ts, --, --))
+>T : Symbol(T, Decl(library.d.ts, --, --))
+>U : Symbol(U, Decl(library.d.ts, --, --))
+
+    props: T;
+>props : Symbol(Foo.props, Decl(library.d.ts, --, --))
+>T : Symbol(T, Decl(library.d.ts, --, --))
+
+    state: U;
+>state : Symbol(Foo.state, Decl(library.d.ts, --, --))
+>U : Symbol(U, Decl(library.d.ts, --, --))
+
+    constructor(props: T, state: U);
+>props : Symbol(props, Decl(library.d.ts, --, --))
+>T : Symbol(T, Decl(library.d.ts, --, --))
+>state : Symbol(state, Decl(library.d.ts, --, --))
+>U : Symbol(U, Decl(library.d.ts, --, --))
+}
+
+=== tests/cases/compiler/component.js ===
+import { Foo } from "./library";
+>Foo : Symbol(Foo, Decl(component.js, 0, 8))
+
+export class MyFoo extends Foo {
+>MyFoo : Symbol(MyFoo, Decl(component.js, 0, 32))
+>Foo : Symbol(Foo, Decl(component.js, 0, 8))
+
+    member;
+>member : Symbol(MyFoo.member, Decl(component.js, 1, 32))
+}
+
+=== tests/cases/compiler/typed_component.ts ===
+import { MyFoo } from "./component";
+>MyFoo : Symbol(MyFoo, Decl(typed_component.ts, 0, 8))
+
+export class TypedFoo extends MyFoo {
+>TypedFoo : Symbol(TypedFoo, Decl(typed_component.ts, 0, 36))
+>MyFoo : Symbol(MyFoo, Decl(typed_component.ts, 0, 8))
+
+    constructor() {
+        super({x: "string", y: 42}, { value: undefined });
+>super : Symbol(MyFoo, Decl(component.js, 0, 32))
+>x : Symbol(x, Decl(typed_component.ts, 3, 15))
+>y : Symbol(y, Decl(typed_component.ts, 3, 27))
+>value : Symbol(value, Decl(typed_component.ts, 3, 37))
+>undefined : Symbol(undefined)
+
+        this.props.x;
+>this.props : Symbol(Foo.props, Decl(library.d.ts, --, --))
+>this : Symbol(TypedFoo, Decl(typed_component.ts, 0, 36))
+>props : Symbol(Foo.props, Decl(library.d.ts, --, --))
+
+        this.props.y;
+>this.props : Symbol(Foo.props, Decl(library.d.ts, --, --))
+>this : Symbol(TypedFoo, Decl(typed_component.ts, 0, 36))
+>props : Symbol(Foo.props, Decl(library.d.ts, --, --))
+
+        this.state.value;
+>this.state : Symbol(Foo.state, Decl(library.d.ts, --, --))
+>this : Symbol(TypedFoo, Decl(typed_component.ts, 0, 36))
+>state : Symbol(Foo.state, Decl(library.d.ts, --, --))
+
+        this.member;
+>this.member : Symbol(MyFoo.member, Decl(component.js, 1, 32))
+>this : Symbol(TypedFoo, Decl(typed_component.ts, 0, 36))
+>member : Symbol(MyFoo.member, Decl(component.js, 1, 32))
+    }
+}

tests/baselines/reference/defaultPropsEmptyCurlyBecomesAnyForJs.types

@@ -0,0 +1,81 @@
+=== tests/cases/compiler/library.d.ts ===
+export class Foo<T = {}, U = {}> {
+>Foo : Foo<T, U>
+>T : T
+>U : U
+
+    props: T;
+>props : T
+>T : T
+
+    state: U;
+>state : U
+>U : U
+
+    constructor(props: T, state: U);
+>props : T
+>T : T
+>state : U
+>U : U
+}
+
+=== tests/cases/compiler/component.js ===
+import { Foo } from "./library";
+>Foo : typeof Foo
+
+export class MyFoo extends Foo {
+>MyFoo : MyFoo
+>Foo : Foo<any, any>
+
+    member;
+>member : any
+}
+
+=== tests/cases/compiler/typed_component.ts ===
+import { MyFoo } from "./component";
+>MyFoo : typeof MyFoo
+
+export class TypedFoo extends MyFoo {
+>TypedFoo : TypedFoo
+>MyFoo : MyFoo
+
+    constructor() {
+        super({x: "string", y: 42}, { value: undefined });
+>super({x: "string", y: 42}, { value: undefined }) : void
+>super : typeof MyFoo
+>{x: "string", y: 42} : { x: string; y: number; }
+>x : string
+>"string" : "string"
+>y : number
+>42 : 42
+>{ value: undefined } : { value: undefined; }
+>value : undefined
+>undefined : undefined
+
+        this.props.x;
+>this.props.x : any
+>this.props : any
+>this : this
+>props : any
+>x : any
+
+        this.props.y;
+>this.props.y : any
+>this.props : any
+>this : this
+>props : any
+>y : any
+
+        this.state.value;
+>this.state.value : any
+>this.state : any
+>this : this
+>state : any
+>value : any
+
+        this.member;
+>this.member : any
+>this : this
+>member : any
+    }
+}

tests/cases/compiler/defaultPropsEmptyCurlyBecomesAnyForJs.ts

@@ -0,0 +1,26 @@
+// @allowJs: true
+// @outDir: ./built
+// @filename: library.d.ts
+export class Foo<T = {}, U = {}> {
+    props: T;
+    state: U;
+    constructor(props: T, state: U);
+}
+
+// @filename: component.js
+import { Foo } from "./library";
+export class MyFoo extends Foo {
+    member;
+}
+
+// @filename: typed_component.ts
+import { MyFoo } from "./component";
+export class TypedFoo extends MyFoo {
+    constructor() {
+        super({x: "string", y: 42}, { value: undefined });
+        this.props.x;
+        this.props.y;
+        this.state.value;
+        this.member;
+    }
+}