docs: fix ecmaVersion in one example, add checks

[mdjermanovic]

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

[x] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

While testing eslint/eslint.org#509, I noticed that one example for the strict rule has "ecmaVersion": 6 in the configuration. This works mostly well because 6 is an alias for 2015, but when the example is opened in the Playground, nothing is selected in the ECMA Version list:

What changes did you make? (Give an overview)

1. Updated the mentioned configuration to "ecmaVersion": 2015.
2. Added a new check in tools/check-rule-examples.js - ecmaVersion, if present, must be one of 3, 5, 2015, 2016, ..., 2024 (the latest number). "latest" string is also disallowed because it is unnecessary since it's the default.

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

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[aladdin-add]

but when the example is opened in the Playground, nothing is selected in the ECMA Version list:

Not sure we should update the examples - It seems more of an issue in the playground. Can we fix it in that, I mean, something like normalize the ecmaVersion to year-style, e.g. 6=>2015?

[mdjermanovic]

but when the example is opened in the Playground, nothing is selected in the ECMA Version list:

Not sure we should update the examples - It seems more of an issue in the playground. Can we fix it in that, I mean, something like normalize the ecmaVersion to year-style, e.g. 6=>2015?

Serialized configs are generated by our sites, so I think we don't need to support all variants. That said, the old demo (https://archive.eslint.org/demo) was using the 6, 7, 8... style, thus it's a good idea to normalize ecmaVersion in the Playground to support old links 👍 . I'll add normalization in eslint/eslint.org#509.

But I'd still like to add this check to keep docs' configs consistent. What do you think?

[aladdin-add]

for consistency, I'm fine with it - seems it's most used in the docs.

[nzakas]

LGTM. Just leaving open for a couple of days for others to get a chance to review.

[fasttime]

There are 35 rule examples that use "sourceType": "module" redundantly. If "ecmaVersion": "latest" won't be allowed for consistency reasons, are there any plans to also disallow "sourceType": "module" or "jsx": false?

[mdjermanovic]

There are 35 rule examples that use "sourceType": "module" redundantly. If "ecmaVersion": "latest" won't be allowed for consistency reasons, are there any plans to also disallow "sourceType": "module" or "jsx": false?

Yes, I'm planning to do that in another PR that will update links to send config in the flat format now that eslint/eslint.org#509 is merged.

[fasttime]

LGTM, thanks!