add Optional Chaining

[mysticatea]

This PR adds a new syntax Optional Chaining (?. operator).

Language Spec: tc39/ecma262#1646
ESTree Spec: estree/estree#204

Please mind the ESTree spec is on discussing. It might changes.

Also, this PR adds a parameter to the parseSubscript method. The parameter is used to make shortCircuited property. Therefore, if a plugin doesn't pass the new parameter, acorn cannot make shortCircuited property properly (it become always false).

[staeke]

can this be merged? why the wait?

[franktopel]

We're also waiting for this so we can use this feature with webpack and without Babel.

[larryosborn]

Could this and #890 please be merged? 🙏 It would open up these new language features to the many modules downstream that depend on acorn. It would also brighten up my day-to-day work by being able to use these two operators. It looks like many other people are excited too!

[marijnh]

@mysticatea @nzakas Is there any hope for an ESTree consensus for this on the short run?

[nzakas]

I’ll see if I can push it forward.

[the-phoenix]

@nzakas Any updates do we have? You're about to merge this, right?
Or we can't merge this because of the conflicts here?
(FYI @mysticatea )

[marijnh]

Don't post further impatient queries, or I'm locking this. We're waiting on the ESTree format to stabilize, and this'll be able to get merged as soon as that happens.

[RReverser]

@mysticatea @nzakas Is there any hope for an ESTree consensus for this on the short run?

We have some better idea of what we want, but there are some final details to discuss.

[RReverser]

No, if there were, they would be posted here. Please refrain from spamming the thread.

[mysticatea]

I updated this PR for the approved version of ESTree spec.

[marijnh]

Wonderful! Merged and released as 7.3.0

[illeatmyhat]

Is it possible to backport this to v6 so that the feature is supported in webpack v4?

[RReverser]

@illeatmyhat Can Webpack upgrade to Acorn 7? There are very few breaking change, and they mainly relate to plugin APIs, most of which have already upgraded.

[dosentmatter]

Wonderful! Merged and released as 7.3.0

@marijnh is there a typo in CHANGELOG.md? For 7.1.0, it says

7.1.0 (2020-06-11)
Add support for optional chaining (?.) and nullish coalescing (??).

However,

• this MR was merged on 2020-06-11T07:29:38Z
• 7.3.0 was released on 2020-06-11T07:54:17.900Z
• 7.1.0 was released 2019-09-24T06:34:22.464Z

[marijnh]

You appear to be looking at the changelog for acorn-loose, not acorn.