Provide C interface

[zokier]

Bloaty has a use for Rust name demangling (see bloaty#110). Bloaty being C++ application we'd need to have a C interface to be able use rustc-demangle for that purpose.

I made quick wrapper (zokier/rustc-demangle-clib) but I think it is something that would make sense to have in-tree here.

The exact form of the interface can be discussed further, that wrapper has been made solely for the needs of bloaty.

If agreed, I can polish the the code (add tests and docs) and submit it as PR here.

[zokier]

For further context, bloaty is a elf/mach file size analyzer, which I think would be useful for the wider Rust community if it were able to demangle Rust symbols.

[alexcrichton]

I'd be totally down for supporting this! I think this library would make a great candidate for a C interface :)

If you want to send a PR I'd be more than willing to help take a look and see how we can land it

[zokier]

I hit bit of a snag while implementing this in the same package; rustc-demangle is no_std (which is nice), but crate-types cdylib/staticlib require eh_personality/panic_fmt implementations. While I could add dummy implementations, that would not be appropriate for lib/rlib crate types.

Not sure if this could be resolved with some conditional compilation or feature flag trickery, rust-lang/rust#20267 is bit ambiguous.

Overall this leads me to think that it might be better to have the C library part in its separate crate/package. Is there some general best practice on how this sort of thing is organized? Can the C lib still live in this same source tree as some sort of sub-crate(??) that Cargo then builds separately?

Anyways, my WIP branch is at https://github.com/zokier/rustc-demangle/tree/c_library if you want to take a look. The wrapper function code itself is ready, but I am not able to build a cdylib/staticlib from it.

[alexcrichton]

Aha yes indeed! I was thinking though that the C API would be a separate crate that just links to rustc-demangle, which I think would fix the need for std and lang items?

[alexcrichton]

A good example to go off I think is perhaps the regex-capi crate -- https://github.com/rust-lang/regex/tree/master/regex-capi

[michaelwoerister]

@zokier & @alexcrichton Is there anything blocking this PR? What would be needed to push it over the finish line?

EDIT: I meant to post this on #14.

[alexcrichton]

Nah nothing blocking, just never got around to finishing it I think!