Merge empty delim subtree in proc-macro

crates/ra_proc_macro_srv/src/rustc_server.rs

@@ -76,7 +76,16 @@ fn extend<I: IntoIterator<Item = TokenTree>>(&mut self, trees: I) {
 impl Extend<TokenStream> for TokenStream {
     fn extend<I: IntoIterator<Item = TokenStream>>(&mut self, streams: I) {
         for item in streams {
-            self.subtree.token_trees.extend(&mut item.into_iter())
+            for tkn in item {
+                match tkn {
+                    tt::TokenTree::Subtree(subtree) if subtree.delimiter.is_none() => {
+                        self.subtree.token_trees.extend(subtree.token_trees);
+                    }
+                    _ => {
+                        self.subtree.token_trees.push(tkn);
+                    }
+                }
+            }
         }
     }
 }

crates/ra_proc_macro_srv/src/tests/fixtures/test_serialize_proc_macro.txt

@@ -25,8 +25,7 @@ SUBTREE $
       SUBTREE () 4294967295
         IDENT   feature 4294967295
         PUNCH   = [alone] 4294967295
-        SUBTREE $
-          LITERAL "cargo-clippy" 0
+        LITERAL "cargo-clippy" 0
         PUNCH   , [alone] 4294967295
         IDENT   allow 4294967295
         SUBTREE () 4294967295