Fix: Don't require commas after rest properties (fixes #7297)

[not-an-aardvark]

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

[ ] Documentation update
[x] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
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[ ] Other, please explain:

See #7297

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• I've read the pull request guide
• I've included tests for my change
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What changes did you make? (Give an overview)

This fixes comma-dangle to not require trailing commas after rest properties with experimentalObjectRestSpread enabled, since this is a SyntaxError according to the spec.

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

Nothing in particular.

[mention-bot]

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

[eslintbot]

LGTM

[platinumazure]

LGTM, thanks!

[kaicataldo]

Do we have nodes with the "RestProperty" type in Espree? Or is this for the benefit of other parsers?

[not-an-aardvark]

I haven't seen any RestProperty nodes. I put it there assuming that the name will eventually be RestProperty rather than ExperimentalRestProperty once it's no longer experimental.

[kaicataldo]

I'd like to hear others' opinions on this. My preference would be not to do this "just in case" and instead to add it in when that becomes a reality (or, hopefully, remove the support for "ExperimentalRestProperty" and add in "RestProperty"). If this helps with other parsers that support this syntax (since we do, even though it's still stage 3), then I'm not opposed to it.

[not-an-aardvark]

Incidentally, why does espree add the Experimental prefix? I can understand the need to mark it as experimental, but I would think that is already accomplished by naming the option experimentalObjectRestSpread. When the node name eventually does change, it will almost certainly break downstream users, and that seems unnecessary to me. (Each node can only have one type, so this isn't like CSS vendor prefixes where the experimental and final versions can be supported simultaneously.)

[hzoo]

RestProperty is used in Babel and it was added to estree as experimental/ as well estree/estree@6e4d212

[nzakas]

Espree uses ExperimentalRestProperty because the feature was experimental. If there was a change before the proposal was fully added to the specification (which just happened), we had the ability to ensure that rules could target both the old representation and the official versions (RestProperty). I didn't want people relying on an experimental node without knowing that they were doing so.

When we fully implement the spec, we'll use RestProperty.

[nzakas]

LGTM