The rand crate tries to maintain compatibility with rust 1.22.0, but a recent release of libc now implicitly requires 1.24.0 on osx due to this patch: #1212, which uses a constant function that was stablized in 1.24. It appears that the Travis config is trying to maintain compatibility with 1.13, but this test only runs on Linux.

Now I personally don't care what is the minimum version you want to support, but given how libc is now the most actively used dependency, you drive the minimum version of a lot of the ecosystem, so would it be possible to at least document this requirement, or setup some more test targets to make sure this doesn't happen again accidentally?