documentation: no-unsafe-optional-chaining - add needs ecmaVersion: 2020

[aavmurphy]

The version of ESLint you are using.
7.18.0 (n/a- website doco)

The problem you want to solve.
The no-unsafe-option-chaining rule page ( https://eslint.org/docs/rules/no-unsafe-optional-chaining ) should mention you also need :
parserOptions.ecmaVersion: 2020
(as mentioned here https://eslint.org/blog/2020/07/eslint-v7.5.0-released )

And while you're there, please add to correct examples a simple
obj.foo?.bar

Your take on the correct solution to problem.

Are you willing to submit a pull request to implement this change?

[mdjermanovic]

Hi @aavmurphy, thanks for the issue!

The no-unsafe-option-chaining rule page ( https://eslint.org/docs/rules/no-unsafe-optional-chaining ) should mention you also need :
parserOptions.ecmaVersion: 2020

The rule itself doesn't require ecmaVersion: 2020, the optional chaining syntax requires that. Also, ESLint can be used with third-party parsers like @babel/eslint-parser and @typescript-eslint/parser which support the latest syntax by default, so there is no need to specify ecmaVersion.

I think that mentioning ecmaVersion in the documentation for a rule makes sense only if the rule auto-fixes code to a newer syntax. For example: prefer-object-spread#when-not-to-use-it

And while you're there, please add to correct examples a simple
obj.foo?.bar

PR to add this example is welcome!

[arminyahya]

Hi everyone
I couldn't find any case no-unsafe-optional-chaining auto-fix code.
Do you know any?

[mdjermanovic]

Hi @arminyahya! This rule isn't auto-fixable, since it warns about possible runtime errors and auto-fixes should never change the behavior of the code. I also don't think there are many cases where the rule could provide a suggestion fix.

[arminyahya]

In that case, there is nothing to document. Am i right?

[mdjermanovic]

Nothing about the autofixing, but it makes sense to add obj.foo?.bar as a correct example for this rule, as @aavmurphy suggested, since it's probably the most common usage of optional chaining.

[arminyahya]

Working on this.

[aavmurphy]

Thanks for adding the a.b?.c example.

I still think it worth mentioning: use parserOptions.ecmaVersion: 2020 if you're using the default parser.

I was unaware of this config option, so didn't understand why my correct code was erroring with a syntax error until google came up with the eslint blog post which mentions ecmaversion which in turn explains it.

Aside: Some of the other 'correct' options are beginning to look a bit like line noise (and this from a perl programmer). Could almost do with a complexity/obfuscated warning.

[nzakas]

@aavmurphy Thanks, we've already decided against adding that for the reasons already stated. If you have other feedback for the documentation, can you open a separate issue? It will make it easier for us to track. Thanks!

[nzakas]

@mdjermanovic can this be closed now? It looks like the PR was merged but didn't have a "fixes" tag.

[mdjermanovic]

Yes, the accepted documentation update has been merged (we had "refs" instead of "fixes" probably because the PR addresses only part of this request).