Always depends on std when built with cargo

[jdub]

The following lines mean that libc always depends on std when built with cargo...

#![cfg_attr(not(feature = "cargo-build"), no_std)]

...

#[cfg(feature = "cargo-build")] extern crate std as core;
#[cfg(not(feature = "cargo-build"))] extern crate core;

... which doesn't work when using cargo with a no_std crate and an alternative target (without a cross-compiled std crate, but that's ultimately not what I want anyway).

In an attempt to hack around this, I added the following to my Cargo.toml:

[dependencies.libc]
version = "0.1"
features = []
default-features = false

But this is the build command line:

rustc /home/jdub/.cargo/registry/src/github.com-0a35038f75765ae4/libc-0.1.8/rust/src/liblibc/lib.rs --crate-name libc --crate-type lib -g --cfg feature="default" --cfg feature="cargo-build" -C metadata=ef5cbad4ef5c7a1e -C extra-filename=-ef5cbad4ef5c7a1e --out-dir /home/jdub/src/derp/acpica/target/i686-unknown-linux-gnu/debug/deps --emit=dep-info,link --target ../derp/i686-unknown-linux-gnu.json -L dependency=/home/jdub/src/derp/acpica/target/i686-unknown-linux-gnu/debug/deps -L dependency=/home/jdub/src/derp/acpica/target/i686-unknown-linux-gnu/debug/deps -Awarnings

Part of the challenge here is that the libc crate is just a slim wrapper around the Rust's liblibc, so changing things is probably difficult.

Thoughts or suggestions, though? Should I not use the libc crate at all?

[alexcrichton]

Unfortunately this crate isn't really intended to be used in the #![no_std] use case

[alexcrichton]

Gah sorry hit the button too soon.

To elaborate, this crate isn't intended to be used as part of the #![no_std] use case, and because Cargo unions features then if anything else depends on this crate without saying default-features = false then the feature will be activated (and this will depend on std).

Stay tuned though, with rust-lang/rfcs#1184 implemented we'll definitely mark this as #![no_std]!

[jdub]

Thanks for being so helpful with difficult freestanders like me, @alexcrichton. 😄