feat: ignore IIFE's for no-loop-func rule

[Gautam-Arora24]

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[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[X] Changes an existing rule (template)
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[ ] Add something to the core
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What changes did you make? (Give an overview)

The change proposes to ignore IIFE's inside the loop's block. However, if the function inside the loop is an async or a generator function, the rule still continues to report error.

Fixes: #16902

Is there anything you'd like reviewers to focus on?

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[mdjermanovic]

This would be a false negative:

/* eslint no-loop-func: "error" */

var arr = [];

for (var i = 0; i < 5; i++) {
    arr.push((f => f)(() => i)); // false negative, this is not a call of `() => i`
}

console.log(arr.map(f => f())); // [ 5, 5, 5, 5, 5 ]

Parent of () => i is a function call, but not a call of that function (() => i is an argument, not callee).

[mdjermanovic]

Also, references in nested functions should still be considered unsafe, unless perhaps they're also immediately executed.

/* eslint no-loop-func: "error" */

var arr = [];

for (var i = 0; i < 5; i++) {
    arr.push((() => {
        return () => i; // false negative
    })());
}

console.log(arr.map(f => f())); // [ 5, 5, 5, 5, 5 ]

[mdjermanovic]

Also, we should check if the function is referenced (#16902 (comment)).

Another example:

/* eslint no-loop-func: "error" */

var arr = [];

for (var i = 0; i < 5; i++) {
    (function fun () {
        if (arr.includes(fun)) return i; // false negative
        else arr.push(fun);
    })();
}

console.log(arr.map(f => f())); // [ 5, 5, 5, 5, 5 ]

[Gautam-Arora24]

Also, we should check if the function is referenced (#16902 (comment)).

Another example:

/* eslint no-loop-func: "error" */

var arr = [];

for (var i = 0; i < 5; i++) {
    (function fun () {
        if (arr.includes(fun)) return i; // false negative
        else arr.push(fun);
    })();
}

console.log(arr.map(f => f())); // [ 5, 5, 5, 5, 5 ]

Makes sense, probably we can maintain a functionStack to keep track of currently running functions and use it to find if an IIFE is being referenced inside it or not.

[github-actions]

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[Rec0iL99]

Hi @Gautam-Arora24, are you still working on this?

[Gautam-Arora24]

Hey @Rec0iL99! Apologies, not getting enough time to work on the PR.

[snitin315]

@Gautam-Arora24 No worries, I'll finish the PR.

[snitin315]

Thanks for the PR, closing in favor of #17528