Difference in parameter inference between arrow functions and classic functions

[knutkj]

In the example code below the arrow function has correct type inference while the function example is unable to infer the parameter type and falls back to any.

declare function monitor<T extends (...args: any) => any>(
  extractor: (...args: Parameters<T>) => Record<string, unknown>,
  executor: T,
): (...args: Parameters<T>) => ReturnType<T>;

monitor((p) => ({ p }), (p: number) => p);
monitor((p) => ({ p }), function (p: number) { return p; });

[knutkj]

Note that if we specify type of this (this: void) the function variant is also able to infer the type:

[RyanCavanaugh]

Duplicate #47599

[typescript-bot]

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