export-ns-from support

[jdalton]

Now that export-ns-from has TC39 consensus we should revisit this in acorn.

\cc @mysticatea @adrianheine

[adrianheine]

I would add this to acorn-stage3 if we come to to the conclusion that we don't want to have this in acorn proper at this time.

[jdalton]

@leobalter RE on the stage the normative change with consensus maps to, was your comment suggesting it maps to stage 3? (if stage 3, projects like acorn and eslint won't officially support it).

Update:

Reviewing the notes from the Sept TC39 meeting it looks like consensus was established on a Stage 3 manner, which will then be merged once implementations are there.

Update:

Tracking related engine issues for Chakra, SpiderMonkey, and V8.

[leobalter]

TL;DR It's approved but waiting for implementations to ship (at least 2) before merging it to the specs.

We need to reach out to implementers to get this done landing.

This requirement is equivalent of the one for Stage 3, that's why we have the reference.

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For extra clarification: there is consensus for the feature, but the spec text will be merged only after we have proof it's web compatible (shipping on at least 2 implementations).

[adrianheine]

Implemented in acorn-export-ns-from for now.