libtest filters should include the test crate's name in the string matched against the filter

Let's say I have a whole bunch of .rs files in my tests folder, like:

• floats/lib.rs
• time.rs
• thread.rs
• ...

Now I want to run just the float tests. Naturally I'll do something like cargo test -- float. Sadly that does not work since this runs the tests that have float as a substring in the name of the test (mod1::mod2::test_fn), but the name of the crate is not included.

This is particularly confusing in the rustc repo itself, where ./x test library/{core,std} -- float will run the float tests in libcore but not the one in libstd: libcore has a single large test crate with a module called floats, while std has a bunch of separate test crates, one of which is called floats.

I think libtest should be changed to put the crate name in the string used for filtering, thus avoiding this confusing and surprising behavior.

@rust-lang/libs-api I've been told the libtest CLI API is in your purview. Is there any chance the behavior of filters could be adjusted? This would lead to strictly more tests being included in any given filter, which at least won't silently reduce test coverage (except when combined with --skip) -- but it could theoretically break a setup where that then includes a test that does not actually work.

Start with the libtest filtering implementation and reproduce the issue using separate integration-test crates such as floats/lib.rs and time.rs, running cargo test -- float. Trace how test names are assembled for filtering; done means the test crate name participates in matching without silently excluding existing matches, including the documented --skip caveat.