`rust.test()` target fails to link with lib in non-standard path

[leftmostcat]

Describe the bug
I am building mesa against LLVMSPIRVLib installed in a user prefix, with --pkg-config-path specified in the configuration. A full build of main succeeds. However, adding a rust.test() against an existing static Rust lib requiring LLVMSPIRVLib causes link to fail.

The resulting compile command adds -Clink-arg=${INSTALL_PATH}/libLLVMSPIRVLib.a to the rustc command; it does not add a -L${INSTALL_PATH}. The final cc includes both -l:libLLVMSPIRVLib.a and ${INSTALL_PATH}/libLLVMSPIRVLib.a, and the lack of -L causes it to be unable to find libLLVMSPIRVLib.a.

To Reproduce

• Install https://github.com/KhronosGroup/SPIRV-LLVM-Translator/ under a prefix which is not in ld's search path, e.g. $HOME/.local.
• Attempt to build the libmesa_rust_test target of following mesa branch: https://gitlab.freedesktop.org/orowith2os/oro-mesa/-/tree/unit-tests

Expected behavior
The test should successfully link.

system parameters

• Fedora 42, native build
• Python: 3.13.3
• Meson: 1.8.0
• Ninja: 1.12.1
• Rust: 1.86.0

[leftmostcat]

Cc: @dcbaker

[bonzini]

I cannot reproduce this, but I could not understand what you mean by "the final cc", and maybe that's the important part?

Here is what I have put together:

• lib1/meson.build

project('lib1', 'c')
lib = static_library('lib1', 'lib.c', install: true)
pkg = import('pkgconfig')
pkg.generate(lib)

• lib1/lib.c

int lib1() { return 42; }

• rustproj/meson.build

project('lib1', 'rust')
dep = dependency('lib1')
lib = static_library('lib', 'lib.rs', dependencies: dep)
rust = import('rust')
rust.test('testme', lib)

• rustproj/lib.rs

extern "C" { pub fn lib1() -> std::os::raw::c_int; }

#[cfg(test)]
mod test {
    #[test]
    fn test_lib1() {
        assert_eq!(unsafe { super::lib1() }, 42);
    }
}

Commands:

meson setup lib1 lib1/build  --prefix $PWD/prefix
ninja -Clib1/build
meson install -Clib1/build
meson setup rustproj rustproj/build --pkg-config-path $PWD/prefix/lib64/pkgconfig
ninja -Crustproj/build
meson test -Crustproj/build

The test uses -L/home/pbonzini/ff/prefix/lib64 -Clink-arg=-llib1.

If I change the installed prefix/lib64/pkgconfig/lib1.pc file to have Libs: ${libdir}/liblib1.a, I get -Clink-arg=/home/pbonzini/ff/prefix/lib64/liblib1.a in the command line, but linking the test still works.

Can you try modifying the reproducer to show the bug?

[leftmostcat]

I'm unable to get a repro either. What I do notice between the two is that in the mesa case, it's using absolute paths for some libraries. I'm attaching an example log of a failing build.

fail.log

[leftmostcat]

I still can't generate a minimum repro case for this. For some reason I haven't yet diagnosed, meson is using raw linker args for lib1, but is using processed linker args in the mesa case. #14781 forces raw linker args for Rust across the board.

This may not be the right solution, but it certainly fixes the problem at hand. A minimal repro will require more familiarity with meson, as the criteria for which set of args to use isn't obvious.

[bonzini]

Thanks for debugging further.

Unfortunately using raw arguments is not possible, raw=True is really used only in tests and for GNOME's GIR generation tools.

You need to debug why Mesa's raw arguments are converted to use the absolute path, whereas the toy example's do not.

[leftmostcat]

I've managed to force the toy example to use absolute path, but not to get rustc to do additional dependency resolution. I asked about this over on zulip (https://rust-lang.zulipchat.com/#narrow/channel/122651-general/topic/rustc.20dependency.20resolution.20with.20-C.20linker.3Dcc). Offering a different workaround while we try to figure out where the disconnect is.

[leftmostcat]

Karol has determined that this has to do with the linked rlibs, which seem to retain information on linked libraries (while assuming the same set of libdirs will be used in linking). I'm not exactly sure how to repro this, however.