Contextual parameters not inferred from variadic tuples with trailing elements

[Andarist]

Bug Report

🔎 Search Terms

tuple arguments trailing elements contextual type

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

declare function test(
  ...args: [...((arg: number) => void)[], (arg: string) => void]
): void;

test(
  (a) => {
    a
    // ^? actual: any; expected: number
  },
  (b) => {
    b
    // ^? actual: any; expected: number
  },
  (c) => {
    c
    // ^? actual: any; expected: string
  },
);

🙁 Actual behavior

Contextual parameters can't be inferred.

🙂 Expected behavior

Contextual parameters should be inferred.

---

Quoting @ahejlsberg from here:

This would require us to reason about elements at a fixed offset from the end of a tuple. We currently only reason about elements at a fixed offset from the start. It adds some more complexity, but it is certainly possible to do.