Make cargo's testsuite faster

[dwijnand]

Would splitting up the tests so it doesn't all build into a big testsuite binary make iterating faster?

I'm not 100% convinced myself (but I thought I'd share my thought with the team anyway) because I think the incremental compiler should solve this problem, so is the real problem that we have too many huge test files? (tests/testsuite/test.rs is 3500 lines, tests/testsuite/build.rs is approaching 5000).

[ehuss]

How much time does it typically take to build the testsuite? For me, small changes take about 10s.

It was unified as part of #4867 where having them completely split up was also expensive.

I wonder if it would help much to remove linking cargo-the-lib. Almost all of the tests are just exercising the cargo executable. The few tests that actually use the library could be separated. It looks like there are a few path-related utility functions that could probably have some way of sharing. I suspect it wouldn't help dramatically, though.

[dwijnand]

Huh, interesting. Thanks, @ehuss.