TS2769 : Function.bind

Bug Report

🔎 Search Terms

function bind

🕗 Version & Regression Information

TypeScript 4.1 & 4.2-beta

⏯ Playground Link

playground

💻 Code

type Funcs = {
    first (value: string): void;
    second (value: number): void;
}

type Store = {
    commit <Name extends keyof Funcs> (
        name: Name,
        ...args: Parameters<Funcs[Name]>
    ): void;
}

type Func <Name extends keyof Funcs> = (
    ...args: Parameters<Funcs[Name]>
) => void;

declare const store: Store;

function commit<Name extends keyof Funcs> (name: Name): Func<Name> {
    // error
    return store.commit.bind(undefined, name);
}

function commit2<Name extends keyof Funcs> (name: Name): Func<Name> {
    return function (...args: Parameters<Func<Name>>) {
        // correct
        store.commit(name, ...args);
    }
}

🙁 Actual behavior

(method) commit<Name extends keyof Funcs>(name: Name, ...args: Parameters<Funcs[Name]>): void
No overload matches this call.
  Overload 1 of 6, '(this: (this: undefined, arg0: Name, ...args: [value: string] | [value: number]) => void, thisArg: undefined, arg0: Name): (...args: [value: string] | [value: number]) => void', gave the following error.
    The 'this' context of type '<Name extends keyof Funcs>(name: Name, ...args: Parameters<Funcs[Name]>) => void' is not assignable to method's 'this' of type '(this: undefined, arg0: Name, ...args: [value: string] | [value: number]) => void'.
      Types of parameters 'args' and 'args' are incompatible.
        Type '[value: string] | [value: number]' is not assignable to type 'Parameters<Funcs[Name]>'.
          Type '[value: string]' is not assignable to type 'Parameters<Funcs[Name]>'.
  Overload 2 of 6, '(this: (this: undefined, ...args: Name[]) => void, thisArg: undefined, ...args: Name[]): (...args: Name[]) => void', gave the following error.
    The 'this' context of type '<Name extends keyof Funcs>(name: Name, ...args: Parameters<Funcs[Name]>) => void' is not assignable to method's 'this' of type '(this: undefined, ...args: Name[]) => void'.
      Types of parameters 'name' and 'args' are incompatible.
        Type 'Name[]' is not assignable to type '[name: Name, ...args: Parameters<Funcs[Name]>]'.
          Target requires 2 element(s) but source may have fewer.(2769)

🙂 Expected behavior

The function commit works correctly as the function commit2. I'm a bit confused and sorry if this bug has been reported.

Start with the linked TypeScript Playground and reproduce the TS2769 error using the generic commit and store.commit.bind example under TypeScript 4.1 or 4.2-beta. No repository file or test is named, so trace the compiler handling of Function.bind and generic parameter tuples; done means commit type-checks with the same behavior as commit2.