Can't infer from `this` type on static class method call in JS Doc

[dead-claudia]

Bug Report

🔎 Search Terms

• js inference
• javascript inference

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about differing type inference for JS and TS

💻 Code

JavaScript:

/** @template R */
export class Action {
    /**
     * @returns {R}
     */
    action() {
        throw new Error("This method is abstract!")
    }

    /**
     * @template {new () => Action<any>} C
     * @this {C}
     * @return {C extends new () => Action<infer T> ? T : never}
     */
    static run() {
        return new this().action()
    }
}

/** @extends {Action<number>} */
export class Foo extends Action {
    action() {
        return 1
    }
}

const handle = Foo.run()

Compiler Options

{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "alwaysStrict": true,
    "esModuleInterop": true,
    "checkJs": true,
    "allowJs": true,
    "declaration": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "target": "ES2017",
    "jsx": "react",
    "module": "ESNext",
    "moduleResolution": "node"
  }
}

Playground Link: Provided

TypeScript:

export abstract class Action<R> {
    action(): R {
        throw new Error("This method is abstract!")
    }

    static run<C extends new () => Action<any>>(
        this: C,
    ): C extends new () => Action<infer T> ? T : never {
        return new this().action()
    }
}

export class Foo extends Action<number> {
    action() {
        return 1
    }
}

const handle = Foo.run()

Output

export class Action {
    action() {
        throw new Error("This method is abstract!");
    }
    static run() {
        return new this().action();
    }
}
export class Foo extends Action {
    action() {
        return 1;
    }
}
const handle = Foo.run();

Compiler Options

{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "alwaysStrict": true,
    "esModuleInterop": true,
    "declaration": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "target": "ES2017",
    "jsx": "react",
    "module": "ESNext",
    "moduleResolution": "node"
  }
}

Playground Link: Provided

🙁 Actual behavior

The inferred type for handle to in the JS version is any, and the --noImplicitAny option is not respected.

🙂 Expected behavior

The inferred type for handle to be number for both, as the types are fully equivalent.

[dead-claudia]

Did this get missed?

[RyanCavanaugh]

This can be vastly simplified:

export class Test {
    /**
     * @template C
     * @this {C}
     * @return {C}
     */
    static test() {
        return this;
    }
}
// p: any, should be p: typeof Test
const p = Test.test();

[dead-claudia]

@RyanCavanaugh Yeah, I tried simplifying it further, but wasn't quite able to get it that simple. 😅

[a-tarasyuk]

@RyanCavanaugh It seems that the problem is not limited to static methods.

export class Test {
    /**
     * @template T
     * @this {T}
     * @return {T}
     */
    test() {
        return this;
    }
}

const t = new Test();
const p = t.test(); // any?
p;

Playground

I think it's because getThisTypeOfSignature doesn't try to resolve the @this tag. Do we need to handle the The_this_context_of_type_0_is_not_assignable_to_method_s_this_of_type_1_2684 error in this case? Since getTypeOfSymbol(signature.thisParameter) can return instantiated this type, I don't know how we can do that for @this tag...