Hard error compiling libc 0.2.36: #![feature(link_cfg)] missing ?

[gnzlbg]

 Compiling libc v0.2.36
error[E0658]: is feature gated (see issue #37406)
   --> /cargo/registry/src/github.com-1ecc6299db9ec823/libc-0.2.36/src/unix/mod.rs:279:9
    |
279 |         #[link(name = "c", kind = "static", cfg(target_feature = "crt-static"))]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: add #![feature(link_cfg)] to the crate attributes to enable

[gnzlbg]

Seems to only fail when building libc with --no-default-features on some targets:

• arm-unknown-linux-musleabi
• armv7-unknown-linux-musleabi
• i686-unknown-linux-musl
• x86_64-unknown-linux-musl

[gnzlbg]

Looks like libc's CI does not test building libc with --no-default-features... opening an issue about this: #929

[alexcrichton]

Argh this definitely wasn't intentional. Although I'm not sure that the no_std build of the musl version of libc would work otherwise...

[gnzlbg]

They used to work last month just fine :/

[alexcrichton]

I forget which PR caused this at this point but I think it's fine to fix whenever basically

[gnzlbg]

yeah I am working on a fix :)

[gnzlbg]

I don't know if we just need to enable the nightly feature and require nightly for no-std builds, or if there is something better that we can do like not using the link attribute somehow. Requiring nightly for libc is... probably a bad idea.

[alexcrichton]

Yeah I don't think we should require nightly for no_std builds, but rather we just need to compile it differently when included in libstd and when included in cargo