oxc feat(ast_tools): pre-compile `#[ast]` macro output

Work in progress.

Generate code for #[ast] macro with an oxc_ast_tools generator.

oxc_ast_macros crate now has no dependencies (no syn etc).

The guts of it is the code! macro. This is the same as quote!, except it evaluates to a TokenStream of code to create the TokenStream which quote! evaluates to.

Unfortunately I'm not seeing an improvement in compile times, because other dependencies of oxc_ast also use syn, so it doesn't drop from the dependency graph. ~~The generated code is 3000 lines, and could likely be shrunk down, which also could help.~~ The generated code is now 600 lines, and now there is a 5% reduction in debug build time for oxc_ast crate - but that's still a disappointingly small improvement.

Am opening this PR not necessarily with the intent of merging it, but to discuss whether this is maybe a useful approach. @rzvxa would appreciate your feedback.

Note: This technique would allow #[generate_derive] to inject the derived impl next to the type def, same as #[derive] does, which would solve the problem of types/fields needing to be pub(crate).

Sep 15 '24 23:09 overlookmotel

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