Parsing a whole crate with particular cfgs defined

[gnzlbg]

I was thinking about porting the ctest crate (used by libc) to syn, mainly because it uses the latest release of the syntex_syntax crate which does not support repr(transparent), and that blocks adding APIs that could benefit from repr(transparent) to libc.

I have a couple of questions and am not sure where is the best place to ask them.

The syntex_syntax crate has a parse_crate function, that given a file, continues walking the directory tree parsing modules, it can do a certain level of macro expansion while doing this (e.g. cfg(unix), etc. where these macros are defined in the session).

I was wondering if syn has something similar, or what would be the best way of achieving the same thing.

I thought that maybe I could parse a single file, then do a fold on the file that expands some macros, then visit all the modules, resolve their paths in the file-system, and repeat. Something like this seems widely-useful enough that it might be worth it to implement it in syn directly instead.

E.g. the ctest crate defines, for each target-triple, which macros should be expanded, but that sounds manual and brittle. It might be better to somehow hook up rustc_target and obtain this information from there.

[dtolnay]

Syn is only a parser, so other aspects of compilation like expanding macros, dealing with target-specific configuration properties, crawling the filesystem, etc are out of scope.

https://github.com/TedDriggs/syn-inline-mod looks like it handles some of what you need.

[gnzlbg]

I see, I'll check that out, thanks!

[gnzlbg]

@dtolnay is there a crate for expanding macros ? Like in the project you mention:

#[cfg(foo)] 
mod a;

is expanded to

#[cfg(foo)]
mod a {
   ...a contents...
}

This gives me an AST for the whole crate, but now I'd like to define some macros, and expand them, e.g., removing all those cfgs, cfg_if!, etc.

[dtolnay]

I don't know of such a crate.