create an empty file even in case of MetadataKind::None

Author: m-ysk

compiler/rustc_metadata/src/fs.rs

@@ -68,13 +68,24 @@ pub fn encode_and_write_metadata(
         .unwrap_or_else(|err| tcx.sess.fatal(&format!("couldn't create a temp dir: {}", err)));
     let metadata_tmpdir = MaybeTempDir::new(metadata_tmpdir, tcx.sess.opts.cg.save_temps);
     let metadata_filename = metadata_tmpdir.as_ref().join(METADATA_FILENAME);
+    let need_metadata_file = tcx.sess.opts.output_types.contains_key(&OutputType::Metadata);
     let metadata = match metadata_kind {
         MetadataKind::None => {
-            if tcx.sess.opts.json_artifact_notifications {
-                tcx.sess
-                    .parse_sess
-                    .span_diagnostic
-                    .emit_artifact_notification(&out_filename, "metadata");
+            if need_metadata_file {
+                // Though creating the empty file here seems to be meaningless, cargo expects it.
+                if let Err(e) = std::fs::File::create(&out_filename) {
+                    tcx.sess.fatal(&format!(
+                        "failed to create the file {}: {}",
+                        out_filename.display(),
+                        e
+                    ));
+                }
+                if tcx.sess.opts.json_artifact_notifications {
+                    tcx.sess
+                        .parse_sess
+                        .span_diagnostic
+                        .emit_artifact_notification(&out_filename, "metadata");
+                }
             }
             EncodedMetadata::empty()
         }
@@ -83,7 +94,6 @@ pub fn encode_and_write_metadata(
 
             let _prof_timer = tcx.sess.prof.generic_activity("write_crate_metadata");
 
-            let need_metadata_file = tcx.sess.opts.output_types.contains_key(&OutputType::Metadata);
             let (metadata_filename, metadata_tmpdir) = if need_metadata_file {
                 if let Err(e) = non_durable_rename(&metadata_filename, &out_filename) {
                     tcx.sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e));