Add Missing Function Declaration: Does Not Correctly Declare Generic Function

[Jutanium]

Bug Report

The "Quick Feature" allows us to generate a missing a function, but doesn't correctly declare that function when its parameters include a type parameter.

See also unexpected behavior when type narrowing in this example.

🔎 Search Terms

• add missing function declaration
• generic type parameter

🕗 Version & Regression Information

I am unable to find a version of TypeScript where this was not a problem.

⏯ Playground Link

Playground link with relevant code

💻 Code

function identity<T>(self: T) {
 
  // To reproduce the bug, Quick Fix > Add missing function declaration
  runEvilSideEffect(self)

  return self;
}

🙁 Actual behavior

TypeScript generated this function, which is an invalid function declaration:

function runEvilSideEffect(self: T) {
    throw new Error("Function not implemented.");
}

🙂 Expected behavior

function runEvilSideEffect<T> (self: T) {
    throw new Error("Function not implemented.");
}

[fatcerberus]

No doubt the current behavior is bad, but the question is which "correct" behavior is more useful: making the generated function generic as suggested here, or to just use the constraint of T?

[RyanCavanaugh]

making the generated function generic as suggested here, or to just use the constraint of T?

🤷‍♂️