since different platforms have subtle differences (libc in this case) i want to run configuration tests from build.rs.
That is:
For each 'feature' defined in Cargo.toml check if there is a conf_test/feature.rs, if so then try to compile (which may already fail) and run it. When both succeeds then enable that feature.
So far so good, I got that mostly working. What is lacking is that haven't found a way how to get the library path that cargo passes to build.rs with the --extern flag. Is there any way to access that or get cargo to tell me about the libraries used and resolve the paths?
UPDATE:
'cargo rustc --message-format json -- --emit metadata' would give me the the data, but calling cargo from cargo blocks, possibly because it waits for a lock in the build directory.
UPDATE2:
'cargo rustc --target-dir ...' fixed the locking problem. I hope that solved all problems.
autocfg - Rust might or might not help to automate some of these. It's geared towards rust's own features, but I think could be used to, eg, test the size_of cint and such.
currently if some (O_PATH, O_DIRECTORY, O_SEARCH) flags are supported in libc::open() and later as well availability of some non-standard functions like statx() renameat2(). more to come.
The libs I want to test against are the ones used for the build, It may become a problem when these tests cant be executed, but I'll support fallbacks for manual overrides. Anyway i may just offer testing for successful compilation without running it. Will consider that in future.
FYI: first step was to abstract the OS-capabilities into cargo features. By that the configuration is done in Cargo.toml and not littered all over the code.
Next step would be this 'conf_tests/' thing because maintaining lists of supported features per OS would be a cumbersome, failure-prone task (At least I don't even know what features all the OS'es support do or do not support) besides the featureset may be even changing with new kernels/libc versions.
