modules/rust: Specify the compiler version to bindgen when possible

bindgen by default may output code that an older rustc cannot
successfully consume. To avoid this, we check if bindgen supports the
rustc version we're using, if so, and if the user didn't set the
`--rust-target` option, we will supply it to ensure that bindgen writes
out code our rustc can use. If it does not support that version
explicitly, we leave it at the default, assuming that our compiler
version is newer than bindgen.

1 files changed, 20 insertions, 3 deletions

diff --git a/mesonbuild/modules/rust.py b/mesonbuild/modules/rust.py
index 60a58698c..5072e503e 100644
--- a/mesonbuild/modules/rust.py
+++ b/mesonbuild/modules/rust.py
@@ -62,6 +62,10 @@ class RustModule(ExtensionModule):
     def __init__(self, interpreter: Interpreter) -> None:
         super().__init__(interpreter)
         self._bindgen_bin: T.Optional[T.Union[ExternalProgram, Executable, OverrideProgram]] = None
+        if 'rust' in interpreter.compilers.host:
+            self._bindgen_rust_target: T.Optional[str] = interpreter.compilers.host['rust'].version
+        else:
+            self._bindgen_rust_target = None
         self.methods.update({
             'test': self.test,
             'bindgen': self.bindgen,
@@ -250,6 +254,15 @@ class RustModule(ExtensionModule):
 
         if self._bindgen_bin is None:
             self._bindgen_bin = state.find_program('bindgen', wanted=kwargs['bindgen_version'])
+            if self._bindgen_rust_target is not None:
+                # ExternalCommand.command's type is bonkers
+                _, _, err = mesonlib.Popen_safe(
+                    T.cast('T.List[str]', self._bindgen_bin.get_command()) +
+                    ['--rust-target', self._bindgen_rust_target])
+                # Sometimes this is "invalid Rust target" and sometimes "invalid
+                # rust target"
+                if 'Got an invalid' in err:
+                    self._bindgen_rust_target = None
 
         name: str
         if isinstance(header, File):
@@ -317,9 +330,13 @@ class RustModule(ExtensionModule):
                 '@INPUT@', '--output',
                 os.path.join(state.environment.build_dir, '@OUTPUT0@')
             ] + \
-            kwargs['args'] + inline_wrapper_args + ['--'] + \
-            kwargs['c_args'] + clang_args + \
-            ['-MD', '-MQ', '@INPUT@', '-MF', '@DEPFILE@']
+            kwargs['args'] + inline_wrapper_args
+        if self._bindgen_rust_target and '--rust-target' not in cmd:
+            cmd.extend(['--rust-target', self._bindgen_rust_target])
+        cmd.append('--')
+        cmd.extend(kwargs['c_args'])
+        cmd.extend(clang_args)
+        cmd.extend(['-MD', '-MQ', '@INPUT@', '-MF', '@DEPFILE@'])
 
         target = CustomTarget(
             f'rustmod-bindgen-{name}'.replace('/', '_'),