Support includes in cc_library

[jpsim]

By specifying SYSTEM_HEADER_SEARCH_PATHS in Xcode build settings.

Partially addresses #82.

Allows Yams to compile.

[brentleyjones]

This should be handled by the other mechanisms that collect header include paths. Ideally we don't look at ctx.attr if possible, to allow custom rules to "just work".

Can you debug a bit to see where the disconnect is? We look at CcInfo.compilation_context, which should have these, in _process_search_paths(). Of note, we need to set search paths there to allow generator to transform bazel-out/ and external/ paths.

[brentleyjones]

Looks like cc_library sets these in CcInfo.compilation_context.system_includes. I thought that was going to be for SDK paths, but thankfully it's not.

So, the more complete fix is to parse that in _process_search_paths() and set it to SYSTEM_HEADER_SEARCH_PATHS ingenerator. Also, we should parse -isystem in opts.bzl similar to -iquote and have opts_search_paths have a system_includes.

[jpsim]

Thanks for the guidance (again!). I applied what I think you asked for, and confirmed that Yams is still compiling in Xcode with the changes. Let me know if I misinterpreted something.

[brentleyjones]

Perfect! Thanks!