Libc on osx now requires rust 1.24.0+

[erickt]

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?

[gnzlbg]

@erickt thank you for the report and sorry for the inconvenience.

We should:

• detect whether the Rust version is >= 1.24 in our build.rs file, and define a cfg flag that is used to white-list const fns in those cases. The functions can be exposed as non-const fn in older Rust versions (or not at all).

• run cargo build for nightly, beta, and stable, on all build bots using Rust 1.13 as the stable Rust version

I can look into implementing both of these things.

[gnzlbg]

cc @Stebalien @erickt libc mater builds again down to Rust 1.13. There are a couple of PRs with fixes in the queue. Once those are merged I'll do a new release.

[gnzlbg]

I forgot to mention what I wanted to mention. Would you be able to test if the master branch solves your issues ? (e.g. by creating a PR to your projects that use the libc master branch and letting your CI run?).

[dhardy]

We still appear to have a problem using Rustc 1.22 on OSX: https://travis-ci.org/rust-random/rand/jobs/493719761 (use of mem::size_of as a const fn). Is this because the relevant changes are not in a release yet?

I don't have a Mac platform to test with myself.
See also: rust-random/rand#719

[gnzlbg]

Is this because the relevant changes are not in a release yet?

Yes. The changes are on master, and a release is blocked on the affected parties testing that master does not have these issues.