aee941559 ("rust: recursively pull proc-macro dependencies as well")
had to be reverted (in a66cb97e8) because it broke Mesa cross
compilation. This happened because a C shared library was linked with
a Rust C-ABI static library, which caused it to inherit the proc macro
dependency the Rust static library was linked with.
The right way to handle this is for only Rust targets to inherit proc
macro dependencies from static libraries they link with. A Rust
executable, library, or whatever will need the proc macros its Rust
dependencies use, as illustrated in the test case that I've
reintroduced here.
I've verified that Mesa still cross compiles correctly with this
change. The same failure was also identified by the "rust/21
transitive dependencies" test case, but only when cross compiling, so
it wasn't caught by CI.
Co-authored-by: Xavier Claessens <xavier.claessens@collabora.com>
This reverts commit aee941559c.
The commit being reverted breaks compilation of a major Meson consumer
(Mesa). As a result, various distros are either pinning to <1.4.0 (before
the commit) or performing this same revert downstream.
Fixing a regression takes priority, so let's revert.
Fixes: https://github.com/mesonbuild/meson/issues/12973
When the proc-macro rlib is in a different subdir, it would miss the
needed -L argument and rustc would not find it. Meson was assuming that
proc-macros are only needed when building libraries that uses it, but it
turns out that was wrong, as show by the unit test.
I noticed when building a project that uses a proc macro that Meson
passed -C prefer-dynamic for the executable, and not the proc macro,
while cargo passed -C prefer-dynamic for the proc macro, but not for
the executable. Meson's behavior broke setting -C panic=abort on the
executable.
As far as we can tell, because we explicitly pass each library path to
rustc, the only thing -C prefer-dynamic affects in Meson is how the
standard libraries are linked. Generally, one does not want the
standard libraries to be dynamically linked, because if the Rust
compiler is ever updated, anything linked against the old standard
libraries will likely break, due to the lack of a stable Rust ABI.
Therefore, I've reorganised Meson's behavior around the principle that
the standard libraries should only be dynamically linked when Rust
dynamic linking has already been opted into in some other way. The
details of how this manifests are now explained in the documentation.
Alyssa Ross
Sam James
Xavier Claessens
Dylan Baker