Upgrade to Babel 7

[tylerhou]

Creating this issue for discussion.

There are a few breaking changes in Babel 7 but they all have easy workarounds. I don't think this will change the interface, so we can do a minor semver upgrade (4.11).

Willing to write a PR.

[markelog]

I think that would be awesome! Go for it :) Regards, Oleg

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On 16 Mar 2019, at 05:21, Tyler Hou ***@***.***> wrote: Creating this issue for discussion. There are a few breaking changes in Babel 7 but they all have easy workarounds. I don't think this will change the interface, so we can do a minor semver upgrade (4.2). Willing to write a PR. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub, or mute the thread.

[tylerhou]

#168

[tylerhou]

Moving the discussion from my pull request into here.

There a few issues with the migration. All of our unit tests pass, but seven Babylon 6 tests fail because Babel 7 invalidated some syntax. I tried pulling in the fixtures from @babel/parser, but they have some new experimental features and TypeScript which messes with us. There are also other non-experimental changes in Babel 7 that we don't support: for await (const x of y). 300-500 Babel 7 fixtures are broken.

Some of this we can fix by ignoring trees of tests (we probably don't care about TypeScript, right?). But experimental features are more unclear, and maybe 25% are from new JavaScript syntax. We should care about standardized JavaScript syntax, yet it's a fair bit of work to add all that extra functionality.

I'd like to get a version of CST out that uses Babel 7 because it's blocking me on upgrading my own codebase to Babel 7. We also have breaking changes in the PR I submitted (removal of SpreadProperty and RestProperty). This means that we have to make a major release. But it's probably bad to make multiple major releases in a row (one to upgrade to 7, one for any breaking changes required to fix the Babel fixtures). How do you feel about making a beta 5.0 release that has broken Babel/Babylon tests?

[markelog]

I guess we can do that, it's beta anyways right?

So the plan is to land #168, release the beta version and then tackle the new syntax - if so, works for me :)