Remove @babel/plugin-transform-regenerator

[tido64]

## Summary

Hermes added support for generators in 0.2.0, and JSC is ES6 feature complete since r202125.

Test plan

n/a

[tido64]

@motiz88: It'd be great if you could make sure this doesn't break Meta internally.

[motiz88]

Awesome - can you please run Prettier, remove @babel/plugin-transform-regenerator from package.json and update yarn.lock accordingly?

[facebook-github-bot]

@motiz88 has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[motiz88]

Looking good so far - I'm fixing up some minor Meta-internal things and planning to land this on Monday. Thanks for this, @tido64!

[newyankeecodeshop]

This is great. I believe you can also remove babel-plugin-transform-for-of since iteration is also supported in both runtimes. Hopefully the minifier supports the syntax too.

[motiz88]

Hopefully the minifier supports the syntax too.

That is a good point - I'm not actually sure we have a test that would fail if it didn't. @tido64 would you mind checking to see what happens if you run this PR with minify=true? (cc @rh389 re: minifier stuff)

[robhogan]

uglify-es and terser both fully support ES6 so I wouldn’t expect any issue for generators or for/of. uglify-es starts to get ugly for ES7+, which is part of the reason I’m looking to shift the default to terser.

[tido64]

@motiz88: Something's failing internally. Is it because of this change?

This is great. I believe you can also remove babel-plugin-transform-for-of since iteration is also supported in both runtimes.

That's a great idea, but I think it should be a separate PR.

Hopefully the minifier supports the syntax too.

That is a good point - I'm not actually sure we have a test that would fail if it didn't. @tido64 would you mind checking to see what happens if you run this PR with minify=true? (cc @rh389 re: minifier stuff)

How do I turn this on in tests? I tried pasting some of the snapshots in Terser's REPL and Uglify's demo. Terser is fine with the generator function, but UglifyJS doesn't support it. I know uglify-es is supposed to support ES6, but it's deprecated and I see that people are trying to migrate to the former: #661

Is this going to be a problem?

[robhogan]

I know uglify-es is supposed to support ES6, but it's deprecated and I see that people are trying to migrate to the former: #661

There's a bit of history here - uglify-js originally didn't support ES6. The author created uglify-es (originally a harmony branch of mishoo/UglifyJS2) to address that, but that was itself deprecated some time ago in favour of uglify-js, as uglify-js v3 does now support ES6 out of the box. I suspect that demo is just out of date. They all have CLIs:

➜ echo "function* myGenerator(myVar) { yield myVar + 1; }" | npx uglify-js -m
function*myGenerator(e){yield e+1}

➜ echo "function* myGenerator(myVar) { yield myVar + 1; }" | npx terser -m
function*myGenerator(e){yield e+1}

➜ echo "function* myGenerator(myVar) { yield myVar + 1; }" | npx uglify-es -m
function*myGenerator(e){yield e+1}

Terser was originally a fork of mishoo/UglifyJS2 so it has a shared ancestry with uglify-es, and internally we've found it to be closer to uglify-es in output than uglify-js@3 is (#661 turned out to be problematic internally), so we're working to make terser the metro default and we'll probably deprecate metro-minifier-uglify.

TL;DR: Nothing minifier-related to worry about for this PR.

[robhogan]

Something's failing internally. Is it because of this change?

Unrelated - React Native iOS tests are broken at the moment.