Missing explicit return type for static methods using private static methods causes return type inference issues in declaration files

[iSwitchL]

🔎 Search Terms

"javascript private static methods return type inference", "private static method inference error in declaration file"

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about JavaScript private static methods return type inference.

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.9.0-dev.20250406#code/MYGwhgzhAEBiD29oG8BQrqehALmHAlsNAMQBGYATgBQCUK0AvultAA4CuZIR2ehxCjXppWrSgFMcHSgDs4iAHTkqAbgxZmqRkA

💻 Code

foo.ts:

class Foo {

    static #bar() { }

    public static bar() {
        return Foo.#bar;
    }

}

foo.d.ts:

declare class Foo {
    #private;
    static bar(): typeof Foo.__#1@#bar;
}

🙁 Actual behavior

The foo.ts file will compile successfully without errors, but the generated foo.d.ts file will be incorrect because it contains a syntax error (Foo.__#1@#bar, ts(1005)).

As a result, any TypeScript subproject that depends on this compiled code will fail at compile time due to the invalid syntax in the foo.d.ts file.

🙂 Expected behavior

Enforce an explicit return type for the public static bar() method, as the presence of it currently allows bypassing this issue.
Otherwise, adjust how TypeScript infers the return types of JavaScript's private static methods.

Additional information about the issue

No response

[Teruk15]

Hi!! may I work on this?