Filter Rust targets from aspect

[kyle-figure]

rust_library rules contain the CcInfo provider, so the bazel aspect does not filter rust_library targets and subsequently fails the build. This PR adds a simple check for the CrateInfo provider, which seems to be the right way to filter out Rust rules.

[erenon]

Thanks, this looks interesting. Why does it fail to build if a rust crate is encountered? Shouldn't it just skip the rs files?

I have two concerns: what if a rust crate is built from cpp sources? Second: this adds a rust dependency to a cpp focused library, which is unfortunate.

[kyle-figure]

clang-tidy binary does not seem check the file extension before executing on a file. You could pass it any arbitrary file and it will fail unless it's a c++ file.

1. You cannot build a rust_library from cpp sources. I believe the proper bazel way of linking cpp object files to a rust binary would be to build a separate cc_library target and add that as a dependency to a rust_binary target. Here is the error message when passing a non-rust file in the srcs attribute of a rust_library target: source file '//hello_lib_rs:lib.cpp' is misplaced here (expected .rs)
2. We can remove the dependency on rules_rust and filter .rs files by changing _rules_sources to only add a src if it doesn't end with .rs:

   def _rule_sources(ctx):
   srcs = []
   if hasattr(ctx.rule.attr, "srcs"):
       for src in ctx.rule.attr.srcs:
           srcs += [src for src in src.files.to_list() if src.is_source and not src.basename.endswith(".rs")]
   return srcs

   Let me know if this is preferable and I will make the change.

[erenon]

I think filtering based on the source extension would be preferable. Also, I'd prefer to opt-in the sources that bazel allows (https://bazel.build/reference/be/c-cpp#cc_binary.srcs) instead of removing .rs files. This would work for other languages. Thanks!

[erenon]

Thanks!