feat(parser,codegen): print comment

[Boshen]

Research

After studying babel, esbuild and prettier, I'm leaning towards storing extra data for linking ast node and comments, the data is processed and saved in the parser.

References:

• Babel - https://github.com/babel/babel/blob/main/packages/babel-parser/ast/comment-attachment.md https://github.com/babel/babel/blob/42cbc1c34264918b8072a5565f8599519351c8ff/packages/babel-parser/src/parser/comments.ts#L117
• Prettier - https://github.com/prettier/prettier/blob/main/src/main/comments/attach.js
• Esbuild - the parser only saves special comments and print them in its printer

We have the following requirements:

• jsdoc linter currently tries to find jsdoc comments in a very inefficient way, it is preferred to do a reverse look up of where the comment is attached
• oxc_prettier needs comment attachment info for printing comments
• oxc_codegen needs to print special comments for bundlers, e.g. webpack / vite special comments and side effect comments
• Rolldown needs to add comments to newly inserted nodes, or in arbitrary locations

---

Proposal

1. Port https://github.com/babel/babel/blob/main/packages/babel-parser/ast/comment-attachment.md
2. Add a storage in Trivias for associating ast nodes, preferably AST node ID (we can use the allocator address API today) to ASTKind

[Boshen]

https://github.com/evanw/esbuild/blob/cc74e6042a9f573bf58e1e3f165ebda70af4ad3b/internal/js_printer/js_printer.go#L281

[SKT1yang]

Is it possible to configure parsing and retain all comments

[ArnaudBarre]

I'll need at least the esbuild behaviour to make the transformer a viable Vite plugin!

[airhorns]

Just to weigh in a little to help prioritize -- without comments, the isolatedDeclarations transform is not super useful in its current form. I think anyone building.d.ts files for consumption intends for them to be consumed by humans, like .d.ts files within a node modules that power typechecking and autocomplete. Stripping all the nice documentation or explanation about these files makes those artifacts far far less useful for humans, and much different than the ones that the TypeScript compiler itself would produce.

I know this is probably a super annoying and invasive change to make to oxc but as someone who adopted and then had to un-adopt the isolatedDeclarations transform because of this missing piece, it'd be really great to get actual drop in compatibility with tsc!

[Boshen]

Codegen now prints useful comments such as jsdoc, vite / webpack specials, pure annotations.

The remaining issue is print all comments, which is really difficult, I'll revisit them when requirements arises. Close as finished in the meantime.

[ArnaudBarre]

Yeah you can get to at least 38m downloads without printing comments 😁