Tracking issue for customizing CRT linkage

- Add the crt-static target-feature
- Update Cargo to pass through target-feature to build scripts - Expose rustc cfg values to build scripts cargo#3243
- Implement "lazy link attributes" and implement in a gated fashion in liblibc.

Be aware that "lazy link attributes" (#[link(name = "foo", cfg(foo))]) will never be stable.

Rollup merge of rust-lang#37545 - alexcrichton:crt-static, r=brson

So apparently, libc fails to compile on MUSL for me because of this feature:

error: is feature gated (see issue #37406)
   --> /home/clar/.cargo/registry/src/github.com-1ecc6299db9ec823/libc-0.2.26/src/unix/mod.rs:227:9
    |
227 |         #[link(name = "c", kind = "static", cfg(target_feature = "crt-static"))]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: add #![feature(link_cfg)] to the crate attributes to enable

error: is feature gated (see issue #37406)
   --> /home/clar/.cargo/registry/src/github.com-1ecc6299db9ec823/libc-0.2.26/src/unix/mod.rs:228:9
    |
228 |         #[link(name = "c", cfg(not(target_feature = "crt-static")))]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: add #![feature(link_cfg)] to the crate attributes to enable

But this appears to be stabilised? Am I missing something?

(note: this is via cargo build --release --target x86_64-unknown-linux-musl)

@clarcharr I believe that's because it's stable in 1.19, which is gonna get released in like 45 minutes.

@steveklabnik

@steveklabnik sorry, I should have clarified that this is on nightly.

It looks like the issue is more about using the cfg(target_feature), rather than crt-static itself? Since #29717 is still open, i bet that's what's going on.

libc should not be relying on the link_cfg feature except when built as part of the standard library. When built as a normal crates.io crate that attribute should not exist, which means it is likely a bug in libc.

@shizmob

/cc @shizmob

@retep998

@retep998 I'm having trouble imagining this as a bug in libc considering how musl is a tested target; maybe a recent change triggered this?

The syntax #[link(name = "c", kind = "static", cfg(target_feature = "crt-static"))] is intended to be an unstable detail only used for libc when built as part of the standard library because the standard library is compiled at a point where it does not know whether the user wants a static CRT or dynamic CRT.

As far as I can tell by looking at the code, that attribute should only even be activated during a cargo build when you've opted out of the use_std default feature. However I see that CI does test cargo build --no-default-features which makes me wonder whether it is testing that target. Because it doesn't explicitly specify --target that means.... it isn't actually testing that target until it does the docker tests, which never build the crate with --no-default-features!

aha!

I'll link this in a comment on libc to point out that the musl build is indeed failing.

This issue is still linked to in errors for #[link(cfg(foo))], so shouldn't it still be open?

@varkor

@varkor

This issue is still linked to in errors for #[link(cfg(foo))], so shouldn't it still be open?

It's better to make a new issue (or remove reference to this issue from the feature gate).

I've opened #72059, though I haven't had time to look into the state of this feature.

Rollup merge of rust-lang#108549 - clubby789:fix-link-cfg-issue, r=eholk

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Tracking issue for customizing CRT linkage #37406

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Tracking issue for customizing CRT linkage #37406

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clarfonthey commented on Jul 20, 2017

steveklabnik commented on Jul 20, 2017

clarfonthey commented on Jul 20, 2017

QuietMisdreavus commented on Jul 20, 2017

retep998 commented on Jul 20, 2017

jirutka commented on Jul 20, 2017

clarfonthey commented on Jul 20, 2017

retep998 commented on Jul 20, 2017

clarfonthey commented on Jul 20, 2017

varkor commented on Apr 3, 2020

petrochenkov commented on May 9, 2020

varkor commented on May 9, 2020

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