Extract to function uses overly generic return type

Bug Report

🔎 Search Terms

• refactor
• extract function

🕗 Version & Regression Information

5.0.0-dev.20230130

💻 Repo

function foo(a: string | undefined): void { }

foo('a' + 'b')

Select 'a' + 'b' and run extract to function

🙁 Actual behavior

The resulting function has a return type of string | undefined

function foo(a: string | undefined): void { }

foo(newFunction())

function newFunction(): string | undefined {
    return 'a' + 'b';
}

This prevents easily re-using this function in other locations

🙂 Expected behavior

The function should have a return type of string

Reproduce the issue with the TypeScript example by selecting 'a' + 'b' and running the extract-to-function refactoring. Start by locating the implementation and tests for that refactoring, then verify that the extracted function is inferred with a string return type rather than string | undefined.