[isolatedDeclarations] Optional parameter in arrow function typed as imported generic type gets emitted as `any`

[MichaelMitchell-at]

🔎 Search Terms

isolated declarations transpiledeclarations any arrow

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play/?noCheck=true&isolatedDeclarations=true#code/JYWwDg9gTgLgBAbxgTzAUzgMQhAvnAMyghDgHICcyBuAKFrQA9JY4BjCAOwGd4AjAIZQ4AXjgAeACoAaAHwAKShAD8ALiw4psgJTqAbhGAATUbMS46QA

💻 Code

import {type Foo} from 'foo';

export const bar = <T,>(foo?: Foo<T>): void => {};

🙁 Actual behavior

With "isolatedDeclarations": true this gets emitted as

export declare const bar: <T>(foo?: any) => void;

🙂 Expected behavior

This gets emitted as

import {type Foo} from 'foo';

export declare const bar: <T>(foo?: Foo<T>) => void;

Additional information about the issue

No response

[a-tarasyuk]

@RyanCavanaugh I've checked and created PR #59446, and the emitter seems to be working as expected. @MichaelMitchell-at, could you provide more details on the cases that cause the issue?

[MichaelMitchell-at]

@a-tarasyuk thank you for the fix! The only example I had found so far in our code base basically boils down to the example I provided. At the time I just worked around it by rewriting it as a function declaration.

[jakebailey]

For reference, this was fixed by #60195.