Unify assertions AST with Babel

[thorn0]

The Babel team named the node property assertsModifier, not asserts. Let's rename it while it's not too late, shall we?

babel/babel#10543

[bradzacher]

Shouldn't it be the other way round?
We've had this merged and released for 2 weeks (2 minor releases), so it is well and truly out there. Changing it would require a breaking change.

Babel merged theirs in 44 minutes ago, and I don't think they've released it - so it'd be better for them to align to us.

[thorn0]

Shouldn't it be the other way round?

Probably. I read this in readme

Some of the people involved in typescript-eslint are also involved in Babel and babel-eslint, and in this project we are working hard to align on the AST format for non-standard JavaScript syntax. This is an ongoing effort.

but didn't know how exactly this process works and which project is considered the source of truth.

[bradzacher]

Looking at that PR, nobody involved in this project was pulled in at all to eyeball, and none of the reviewers are involved here as well.

James has been involved in the babel side of things in the past but he's been pretty busy with real life stuff. We have a few other people who are collaborators on both projects, but then that relies them seeing the work in both repos (or being notified).

[existentialism]

@bradzacher sorry I missed this (been traveling quite a bit). re: alignment, feel free to ping me as things get ready to land here for TS (might even be nice to setup a group to cc with @hzoo and @nicolo-ribaudo too), and we'll be sure /cc you and James on the Babel-side!

[thorn0]

@bradzacher And what is the process supposed to be for the existing differences? E.g. for TSImportType, Babel uses the argument property name, typescript-eslint uses parameter. How are these things going to be aligned?

[bradzacher]

re: alignment

Definitely, I think it makes sense to add a collaborator list here so we can easily tag the relevant babel peeps when we are making / talking about the AST (and vice versa for babel when the TS AST is being worked on).

And what is the process supposed to be for the existing differences

We don't have one!
We need to "sit down and talk" about these differences so that we can figure out what breaking changes are required where so that we can converge the two representations.

There's a bunch of stuff that I've been thinking about around this, because there's a lot of weirdness in the AST.

[nicolo-ribaudo]

We should definitely ping each other when designing new ASTs. We already have a #typescript room in our Slack channel, we might use it for any chat which doesn't fit well the GitHub issue format.

Regarding the AST differences, do you already know the complete set of them?

[bradzacher]

We have a basic alignment pipeline setup in this repo, but since james set it up, it has fallen a bit into disrepair.
Between not keeping it up to date with the latest version of babel, our teams not fully aligning on things (like babel having some props being optional when we always emit them), and some things differing, it's not showing a great state.

Here is a list of our fixtures where the two impls differ in some way.
https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/typescript-estree/tests/ast-alignment/fixtures-to-test.ts

This test can definitely be improved (like ignoring times that we emit prop: false and babel emitting no prop), but it's at least a start.

Side note that we probably need to have a lot more cases added to our fixtures, I know there's a number of edge case gaps that we don't have proper testing for (eg #1100).

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We already have a #typescript room in our Slack channel, we might use it for any chat which doesn't fit well the GitHub issue format.

I just joined the slack + channel