rust/src/test/ui/auxiliary/link-cfg-works-transitive-dylib.rs

#![feature(link_cfg)]

#[link(name = "foo", cfg(foo))]
extern {}
rustc: Implement #[link(cfg(..))] and crt-static This commit is an implementation of [RFC 1721] which adds a new target feature to the compiler, `crt-static`, which can be used to select how the C runtime for a target is linked. Most targets dynamically linke the C runtime by default with the notable exception of some of the musl targets. [RFC 1721]: https://github.com/rust-lang/rfcs/blob/master/text/1721-crt-static.md This commit first adds the new target-feature, `crt-static`. If enabled, then the `cfg(target_feature = "crt-static")` will be available. Targets like musl will have this enabled by default. This feature can be controlled through the standard target-feature interface, `-C target-feature=+crt-static` or `-C target-feature=-crt-static`. Next this adds an gated and unstable `#[link(cfg(..))]` feature to enable the `crt-static` semantics we want with libc. The exact behavior of this attribute is a little squishy, but it's intended to be a forever-unstable implementation detail of the liblibc crate. Specifically the `#[link(cfg(..))]` annotation means that the `#[link]` directive is only active in a compilation unit if that `cfg` value is satisfied. For example when compiling an rlib, these directives are just encoded and ignored for dylibs, and all staticlibs are continued to be put into the rlib as usual. When placing that rlib into a staticlib, executable, or dylib, however, the `cfg` is evaluated as if it were defined in the final artifact and the library is decided to be linked or not. Essentially, what'll happen is: * On MSVC with `-C target-feature=-crt-static`, the `msvcrt.lib` library will be linked to. * On MSVC with `-C target-feature=+crt-static`, the `libcmt.lib` library will be linked to. * On musl with `-C target-feature=-crt-static`, the object files in liblibc.rlib are removed and `-lc` is passed instead. * On musl with `-C target-feature=+crt-static`, the object files in liblibc.rlib are used and `-lc` is not passed. This commit does not include an update to the liblibc module to implement these changes. I plan to do that just after the 1.14.0 beta release is cut to ensure we get ample time to test this feature. cc #37406 2016-10-31 18:40:13 -05:00			`#![feature(link_cfg)]`

			`#[link(name = "foo", cfg(foo))]`
			`extern {}`