rust: proc-macro transitive dependencies should be ignored

Fixes: #12459

mesonbuild/build.py

@@ -1299,6 +1299,8 @@ def get_dependencies_recurse(self, result: OrderedSet[Target], include_internals
         for t in self.link_targets:
             if t in result:
                 continue
+            if isinstance(t, SharedLibrary) and t.rust_crate_type == 'proc-macro':
+                continue
             if include_internals or not t.is_internal():
                 result.add(t)
             if isinstance(t, StaticLibrary):

test cases/rust/20 transitive dependencies/foo.c

@@ -0,0 +1,6 @@
+int foo_rs(void);
+
+int main(void)
+{
+    return foo_rs() == 42 ? 0 : 1;
+}

test cases/rust/20 transitive dependencies/foo.rs

@@ -0,0 +1,9 @@
+extern crate pm;
+use pm::make_answer;
+
+make_answer!();
+
+#[no_mangle]
+pub fn foo_rs() -> u32 {
+    answer()
+}

test cases/rust/20 transitive dependencies/meson.build

@@ -1,4 +1,4 @@
-project('transitive dependencies', 'rust',
+project('transitive dependencies', 'rust', 'c',
   version : '1.0.0',
   meson_version : '>= 1.0.0',
   default_options : ['rust_std=2018'],
@@ -10,3 +10,18 @@ subdir('libb')
 main = executable('main', 'main.rs',
   dependencies : [libb_dep],
 )
+
+# Since foo-rs is a static library, its dependencies are normally added to foo
+# library linker. However, since pm is a proc-macro, foo library should not
+# link with it. In native build this is an harmless overlinking, but in cross
+# building foo and pm are for different arch and it would fail to link.
+rust = import('rust')
+pm = rust.proc_macro('pm', 'proc.rs')
+foo = static_library('foo-rs', 'foo.rs',
+  rust_abi: 'c',
+  link_with: pm,
+)
+exe = executable('footest', 'foo.c',
+  link_with: foo,
+)
+test('footest', exe)

test cases/rust/20 transitive dependencies/proc.rs

@@ -0,0 +1,7 @@
+extern crate proc_macro;
+use proc_macro::TokenStream;
+
+#[proc_macro]
+pub fn make_answer(_item: TokenStream) -> TokenStream {
+    "fn answer() -> u32 { 42 }".parse().unwrap()
+}