Add a test for rust-lang#3004

Author: topecongiro

tests/source/macros.rs

@@ -466,3 +466,8 @@ static ROOTED_TRACEABLES: RefCell<RootedTraceableSet> =
         RefCell::new(RootedTraceableSet::new(1234)) ;
 
 ] ;
+
+fn issue3004() {
+    foo!(|_| { (  ) });
+    stringify!(( foo+ ));
+}

tests/target/macros.rs

@@ -1043,3 +1043,8 @@ thread_local![
     static ROOTED_TRACEABLES: RefCell<RootedTraceableSet> =
         RefCell::new(RootedTraceableSet::new(1234));
 ];
+
+fn issue3004() {
+    foo!(|_| { () });
+    stringify!((foo+));
+}