--print native-static-libs of a staticlib crate does not print libraries linked in via #[link] attribute or -l parameters

[sdroege]

This is with Rust 1.69 but was probably always the case.

Example:

lib.rs

#[no_mangle]
pub extern "C" fn my_staticlib_add(left: i32, right: i32) -> i32 {
    // Obviously makes no sense but...
    unsafe {
        g_free(std::ptr::null_mut());
    }
    left + right
}

#[link(name = "glib-2.0")]
extern "C" {
    fn g_free(p: *mut ());
}

Compiling with

$ rustc --crate-type staticlib --print native-static-libs --edition=2018 --crate-name staticlib --emit link -o libstaticlib.a lib.rs

prints

note: Link against the following native artifacts when linking against this static library. The order and any duplication can be significant on some platforms.

note: native-static-libs: -lgcc_s -lutil -lrt -lpthread -lm -ldl -lc

Similarly when providing -lglib-2.0 nothing changes. I didn't really follow how rustc collects the libraries but I think it's via the native_libraries query in compiler/rustc_middle/src/query/mod.rs which claims

    /// Look up all native libraries this crate depends on.
    /// These are assembled from the following places:
    /// - `extern` blocks (depending on their `link` attributes)
    /// - the `libs` (`-l`) option

so this should be included AFAIU. Also the rationale of native-static-libs was to provide all libraries needed to link to the resulting staticlib, which is not the case in the above example.

---

CC @kornelski who originally implemented this feature.

[Urgau]

It works as expected if the #[link] attribute is used in a dependencies.

It seems to me that the link_staticlib function,

rust/compiler/rustc_codegen_ssa/src/back/link.rs

Lines 478 to 484 in a673ad6

	fn link_staticlib<'a>(
	sess: &'a Session,
	archive_builder_builder: &dyn ArchiveBuilderBuilder,
	codegen_results: &CodegenResults,
	out_filename: &Path,
	tempdir: &MaybeTempDir,
	) -> Result<(), ErrorGuaranteed> {

is forgetting to add the current native libs.

Doing something like this correctly adds -lglib-2.0 to the output (even when passed via the command line) but I don't know if it's the right thing to do (cc @petrochenkov).

all_native_libs.extend_from_slice(&codegen_results.crate_info.used_libraries);

[bjorn3]

Yeah, I think adding all_native_libs.extend_from_slice(&codegen_results.crate_info.used_libraries); is the correct fix. That adds the same information as codegen_results.crate_info.native_libraries does for dependencies.

[kornelski]

Beware that --print native-static-libs is rather quirky. Originally Rust printed lines during build with information which link flags need to be added to use the static library it builds, and --print native-static-libs is a blunt way of redirecting these "warnings". I don't know whether omission of #[link] is a bug or the old warnings just weren't meant to print them.

[bjorn3]

I can't imagine it to be a deliberate omission as --print native-static-libs is the only way to know how to correctly link any arbitrary staticlib afaik.