--print native-static-libs with --emit metadata prints nothing

[ChrisDenton]

It should be possible to print the necessary native libs without actually creating the static library. However, combining --emit metadata with --print native-static-libs does not print anything.

I tried this:

$ rustc /dev/null --print native-static-libs --crate-type staticlib --emit metadata

I expected to see this printed to the console:

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

Instead, this happened: the output is empty.

If I run without --emit metadata it works:

$ rustc /dev/null --print native-static-libs --crate-type staticlib
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

However, this also creates libnull.a.

Meta

rustc --version --verbose:

rustc 1.87.0-nightly (f04bbc60f 2025-02-20)
binary: rustc
commit-hash: f04bbc60f8c353ee5ba0677bc583ac4a88b2c180
commit-date: 2025-02-20
host: x86_64-unknown-linux-gnu
release: 1.87.0-nightly
LLVM version: 20.1.0

[xizheyin]

@rustbot claim

[ChrisDenton]

From what @bjorn3 says this might not be possible. Dependency format information is not calculated if not linking (where "linking" includes making a staticlib).

rust/compiler/rustc_metadata/src/dependency_format.rs

Lines 87 to 89 in 6e23095

	if !sess.opts.output_types.should_link() {
	return IndexVec::new();
	}

This matters because we need some way of filtering for statically linked libs (Linkage::Static) here:

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

Lines 263 to 267 in 6e23095

	match fmts.get(cnum) {
	Some(&Linkage::NotLinked | &Linkage::Dynamic | &Linkage::IncludedFromDylib) => continue,
	Some(_) => {}
	None => return Err(errors::LinkRlibError::MissingFormat),
	}

Otherwise we could print all native libraries but not filter for static ones specifically. Which is not what native-static-libs does.