Multiple #[link(name="X")] attributes result in duplicate link arguments

[nagisa]

Given static libraries, having duplicate -lfoo is more likely to result in an error than not. Having multiple #[link] blocks with kind="static" specified or inferred in any way will cause the linking to fail. Consider for example this:

extern "C" {
    #![link(name="zstd", kind="static")]
    fn ZSTD_freeCCtx();
}

extern "C" {
    #![link(name="zstd", kind="static")]
    fn ZSTD_createCCtx();
}

fn main() {
    unsafe {
        ZSTD_createCCtx();
        ZSTD_freeCCtx();
    }
}

will pass to the linker

"-Wl,--whole-archive" "-lzstd" "-Wl,--no-whole-archive" "-Wl,--whole-archive" "-lzstd" "-Wl,--no-whole-archive"

which will fail due to duplicate symbols. This is somewhat surprising because rustc will avoid passing through to the linker the -lfoo from -l static=foo if there’s a #[link] attribute in the crate.

[nagisa]

Duplicate of #38460