Fix: remove autofix for var undef inits (fixes #9231)

[VictorHom]

What is the purpose of this pull request? (put an "X" next to item)

[X ] Other, please explain: Remove autofixing to no-undef-init rule, particularly for var declarations

What changes did you make? (Give an overview)

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

1. To the point in no-undef-init incorrectly autofixes some var declarations #9231 about not using let: Using let looks like it still works, so I want to make sure I understand.

function fun() {
  for (var p in [0, 1, 2]) {
    let selected = undefined;// auto fix will remove `= undefined`

    for (var i in [0, 1, 2]) {
      if (!selected) {
        console.log('selected');
      }
      selected = i;
    }
  }
}

fun();

2. Is it okay to keep as separate if? I didn't include in the same if as line 50 since the inner comment wouldn't make sense.
3. I am checking node.parent.kind because it looks to distinguish between var and let

[eslintbot]

LGTM

[mention-bot]

@VictorHom, thanks for your PR! By analyzing the history of the files in this pull request, we identified @not-an-aardvark, @ilyavolodin and @vitorbal to be potential reviewers.

[gyandeeps]

we need to avoid var fix only if its inside a loop. I think currently you are completely removing fix for var.

[not-an-aardvark]

@gyandeeps While that might be a better fix, note that completely removing the autofix for var was the solution that I proposed in #9231 (comment).

[not-an-aardvark]

Also, I don't think checking if the variable is in a loop fully solves the issue:

var foo = 5;
var foo = undefined;
foo; // => undefined

var foo = 5;
var foo;
foo; // => 5

[gyandeeps]

you are right @not-an-aardvark ... forgot about that weird case of var... so current plan sounds good...

[not-an-aardvark]

Thanks for the PR! This looks good, I just have a small suggestion.

[not-an-aardvark]

Can you add similar tests to the old versions, but with let? Previously, none of the tests used let because the rule worked the same way with var as it did with let. Now that there is a behavior change between the two types, we should make sure the normal autofixing behavior still works correctly with let. (For example, we should test that let a; gets fixed to let a, b = 1 gets autofixed to let a = undefined, b = 1, and we should test that let [a] = undefined still doesn't get autofixed.)

[eslintbot]

LGTM

[eslintbot]

LGTM

[platinumazure]

LGTM, thanks for contributing!