Rust: Fix both_libraries() case

Rustc does not produce object files we can reuse to build both
libraries. Ideally this should be done with a single target that has
both `--crate-type` arguments instead of having 2 different build rules.

As temporary workaround, build twice and ensure they don't get conflicts
in intermediary files created by rustc by passing target's private
directory as --out-dir.

See rust-lang/rust#111083.

Author: xclaesse

mesonbuild/backend/ninjabackend.py

@@ -1951,10 +1951,9 @@ def generate_rust_target(self, target: build.BuildTarget) -> None:
         # Rustc replaces - with _. spaces or dots are not allowed, so we replace them with underscores
         args += ['--crate-name', target.name.replace('-', '_').replace(' ', '_').replace('.', '_')]
         depfile = os.path.join(target.subdir, target.name + '.d')
-        args += ['--emit', f'dep-info={depfile}', '--emit', 'link']
+        args += ['--emit', f'dep-info={depfile}', '--emit', f'link={target_name}']
+        args += ['--out-dir', self.get_target_private_dir(target)]
         args += target.get_extra_args('rust')
-        output = rustc.get_output_args(os.path.join(target.subdir, target.get_filename()))
-        args += output
         linkdirs = mesonlib.OrderedSet()
         external_deps = target.external_deps.copy()
 

mesonbuild/interpreter/interpreter.py

@@ -3206,6 +3206,10 @@ def build_both_libraries(self, node, args, kwargs):
             # Feel free to submit patches to get this fixed if it is an
             # issue for you.
             reuse_object_files = False
+        elif shared_lib.uses_rust():
+            # FIXME: rustc supports generating both libraries in a single invocation,
+            # but for now compile twice.
+            reuse_object_files = False
         else:
             reuse_object_files = static_lib.pic