parser: add parse-only support for "import.meta"

[wchargin]

Summary:
Resolves #6913. As with new.target, we can parse the expression, but
we fail to typecheck it. Clients can use a suppression comment to ignore
uses of import.meta in an otherwise valid file.

The parse error message on inputs like import.notMeta was chosen to be
consistent with the message emitted by Babylon.

Test Plan:
Unit tests added, and all existing tests pass.

wchargin-branch: parse-import-meta

[facebook-github-bot]

@mroch is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[goodmind]

@mroch is this still on your radar?

[goodmind]

/cc @mroch

[goodmind]

@mroch

[fredericgermain]

@mroch

[wchargin]

I went ahead and merged in changes over the last year, fixed conflicts,
upgraded past a major OPAM and OCaml version boundary, installed bwrap
from source after finding all its dependencies, revised the code due to
some changes in Flow internals, and added a new test. @mroch, it’d be
great if this could be landed so that I don’t have to do this all again
next year! :-)

[wchargin]

Happy birthday! This pull request is two years old. As such, I’ve again
resolved the merge conflicts due to upstream changes, and gotten the
tests passing. @jbrown215, it’d be great if this could be landed so that
I don’t have to do this all again again next year! :-)

[fredericgermain]

You're so brave @wchargin

This issue is the reason I'm going to TypeScript.

I thought Flow was a better idea overall than TypeScript, but the latest versions and the governance of the project made me lose trust in it.

Happy birthday to the issue!

[facebook-github-bot]

@jbrown215 has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[jbrown215]

From @mroch:

I don't think the locs are correct in the error cases, they consume tokens that aren't included in the range and don't point at the entire error (AFAICT).
IMO, should still use with_loc but also grab start_loc if it's needed for that error_at call.

The lint errors are ocamlformat errors. I can fix that on my side!

[FezVrasta]

Any chance to get this PR merged?

[TrySound]

Hi @jbrown215 @mroch! Any new on this feature?

[ancms2600]

Get it merged, you turkeys

[facebook-github-bot]

This pull request has been merged in 0851b3e.

[isker]

Bless.

[gkz]

@ancms2600

Get it merged, you turkeys

There you go
🦃

[FezVrasta]

Is there any way to type import.meta.env?

[gkz]

What should that be? Do you have links to documentation?

[FezVrasta]

It's used by Vite to access environment variables. It works identically to process.env

[gkz]

If I add a [string]: mixed indexer to the type, so you can access random other properties (but they're mixed so you have to refine them first to e.g. a string), would that be fine? We probably don't want to hardcode random specific things like vite env vars in Flow.

So you could do

const env = import.meta.env;
if (typeof env === 'string') {
  // do the stuff
}

[FezVrasta]

I think it would be fine, anyways most of the times all you do is doing a string comparison so even if it's mixed it will work just fine.

Of course having a way to extend such types in user land would be optimal, as import.meta is thought to be user extensible.