Support custom parserOpts for babel parser in @babel/eslint-parser

[vikr01]

Q	A
Fixed Issues?	N/A
Patch: Bug Fix?	N/A
Major: Breaking Change?	N/A
Minor: New Feature?	Yes
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?	No
License	MIT

The README for @babel/eslint-parser states:

• babelOptions passes through Babel's configuration loading and merging options (for instance, in case of a monorepo). When not defined, @babel/eslint-parser will use Babel's default configuration file resolution logic.

However, this hasn't exactly been true, because you can't override all of the babel parser's options. With this, there's now capability to use neat features like the flowComments plugin to lint flow comments just like flow typings.

[vikr01]

So if options.allowImportExportEverywhere exists, it'll use that over parserOpts. allowImportExportEverywhere to prevent breaking changes.

[vikr01]

Seems like the "estree" plugin is necessary for the eslint parser here, so I figured we shouldn't override it.

[vikr01]

@danez You reviewed #9168 from me before, might you be able to review this?

I’d ideally like for us to start using this at Facebook. 🙂

[nicolo-ribaudo]

@vikr01 We might want to do #11334 (comment) instead

[existentialism]

With this, there's now capability to use neat features like the flowComments plugin to lint flow comments just like flow typings.

Somewhat related, but for those who are using a Babel config, we could always support flowComments by augmenting the flow preset to enable comment parsing and/or a new syntax plugin... then with babel-eslint@11 it'd just read the config?

(And yeah, I guess for the whole "passing config programmatically" story, we should roll with #11334 (comment))

[vikr01]

@existentialism Agree — I think enabling the flowComments syntax via the flow preset would be nice.

[vikr01]

@nicolo-ribaudo That looks to be for babel config plugins, this is for the syntax plugins. Don’t the two work differently, or am I mistaken?

[nicolo-ribaudo]

@vikr01 My proposal was to allow passing a full Babel config, so you will also be able to pass parserOpts without special-casing it in our code.

[JLHwung]

In #11639 we allowed pass through all babel options to @babel/eslint-parser. Closing this PR. @vikr01 Thanks for contributing!