Bug Report

🔎 Search Terms

uncalled function checks, negation

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

declare function isFoo(): boolean;
declare const isUndefinedFoo: (() => boolean) | undefined;

if (isFoo) {
    // uncalled function checks already work well here
}

if (!isFoo) {
    // uncalled function checks should cover this case too
}

if (!isUndefinedFoo) {
    // this case should not be covered
}

🙁 Actual behavior

Uncalled function checks do not work with the ! operator.

🙂 Expected behavior

Unless a function may be undefined it would be very helpful to check whether it is called when it is used with the ! operator.

I created this issue to separate a part of the implementation of #42835 resulting from issue #35584. This specific issue was inspired by #35584 (comment).