Add decorators in ESTree for JS files

[ArnaudBarre]

Playground

There are visible in the Rust AST, is this something wanted to not exposed them? It's only stage 3 but given that they are already parsed, I think it's better to make them available than skip them

[Boshen]

blocks https://github.com/ArnaudBarre/prettier-oxc-parser

[overlookmotel]

@ArnaudBarre Same question as #10978 (comment): What other parsers used in Prettier can parse decorators (apart from TS-ESLint)?

I'm struggling to work out how we can test this, because our testing infra is based around comparing to an existing implementation. TS-ESLint adds decorators fields everywhere, like on every Identifier etc. I suspect this is overkill for JS files, and would likely incur a perf hit, but I'm unclear which types should have decorators field, and which shouldn't.

[overlookmotel]

Ah ha I have my answer as to which types should get decorators field: https://github.com/estree/estree/blob/master/stage3/decorators.md

But is there a reference implementation we can use for tests which follows this spec?

[fisker]

What other parsers used in Prettier can parse decorators

flow and meriyah

Same answer #10978 (comment), mentioned in #10979, we can't ignore decorators, we need error to refuse formatting if not planned to support.

[overlookmotel]

Thanks for coming back. Perhaps we can add meriyah to https://github.com/oxc-project/acorn-test262 to generate tests cases for decorators. If meriyah has exactly same output as Acorn, except for decorators and other Stage 3 features, this should not be too tricky. But does it? From aligning with TS-ESLint for TS types, we discovered there are subtle/obscure differences between parsers e.g. treatment of ranges/spans. We'll find out...

I guess another option is to try to conform to @babel/eslint-parser. That would be more future-proof, as new features always get implemented in Babel first.

Either way, I'll need to complete the work on field ordering first (#9705 (comment)), because different parsers definitely differ in that respect.

[Boshen]

oxc-parser has landed in prettier, this is the last blocking issue before its stable release.

https://github.com/prettier/prettier/blob/40d9a7e2b0de094a5468883571a0f2767dd414ac/tests/config/run-format-test.js#L88-L100

[overlookmotel]

Very much aware! I'm working on it.