"Implicitly has type 'any'" when type annotation is provided

Bug Report

🔎 Search Terms

implicit any, filter object properties by type, key remapping

⏯ Playground Link

Playground link with relevant code

💻 Code

type BooleanProperties<T> = T extends any ? { 
  [K in keyof T as T[K] extends boolean ? K : never]: boolean;
} : never;

class Foo {
  booleansOnly: BooleanProperties<this> = undefined!; // Omitted..
  
  getString<F extends (someUsefulData: any) => any>(fn: F) : string {
    return undefined!; // Omitted..
  };

  aBoolean = true;
  
  definitelyAString = this.getString(() => this.booleansOnly.aBoolean);
}

🙁 Actual behavior

Error: ‘definitelyAString’ implicitly has type ‘any’ because it does not have a type annotation and is referenced directly or indirectly in its own initializer.

🙂 Expected behavior

Since “getString” method has an explicit return type (string), in my opinion “type annotation” is provided, and the error should not be thrown.

[RyanCavanaugh]

There’s a good discussion about this in #45213

[MartinJohns]

Maybe adding some kind of syntax to provide Typescript instructions on how to handle circularity errors

It mentioned the option to add a type annotation in the error message.

I hope in the future Typescript will provide a way to handle this kind of sistuations

As far as I know the compiler would have to be rewritten basically from scratch, and introduce a two-phase type check. Very unlikely to happen.