Only write metadata module when necessary

Author: bjorn3

src/lib.rs

@@ -194,7 +194,7 @@ impl CodegenBackend for CraneliftCodegenBackend {
         &self,
         tcx: TyCtxt<'a, 'tcx, 'tcx>,
         metadata: EncodedMetadata,
-        _need_metadata_module: bool,
+        need_metadata_module: bool,
         _rx: mpsc::Receiver<Box<dyn Any + Send>>,
     ) -> Box<dyn Any> {
         env_logger::init();
@@ -323,7 +323,7 @@ impl CodegenBackend for CraneliftCodegenBackend {
             rustc_incremental::save_dep_graph(tcx);
             rustc_incremental::finalize_session_directory(tcx.sess, tcx.crate_hash(LOCAL_CRATE));
 
-            let metadata_module = {
+            let metadata_module = if need_metadata_module {
                 use rustc::mir::mono::CodegenUnitNameBuilder;
 
                 let cgu_name_builder = &mut CodegenUnitNameBuilder::new(tcx);
@@ -342,13 +342,15 @@ impl CodegenBackend for CraneliftCodegenBackend {
                 let obj = metadata_artifact.emit().unwrap();
                 std::fs::write(&tmp_file, obj).unwrap();
 
-                CompiledModule {
+                Some(CompiledModule {
                     name: metadata_cgu_name,
                     kind: ModuleKind::Metadata,
                     object: Some(tmp_file),
                     bytecode: None,
                     bytecode_compressed: None,
-                }
+                })
+            } else {
+                None
             };
 
             return Box::new(CodegenResults {
@@ -369,7 +371,7 @@ impl CodegenBackend for CraneliftCodegenBackend {
                 } else {
                     None
                 },
-                metadata_module: Some(metadata_module),
+                metadata_module,
                 crate_hash: tcx.crate_hash(LOCAL_CRATE),
                 metadata,
                 windows_subsystem: None, // Windows is not yet supported