enforce parsing invariant for patterns

crates/parser/src/grammar.rs

@@ -109,6 +109,19 @@ pub(crate) mod entry {
             items::mod_contents(p, false);
             m.complete(p, MACRO_ITEMS);
         }
+
+        pub(crate) fn pattern(p: &mut Parser) {
+            let m = p.start();
+            patterns::pattern_single(p);
+            if p.at(EOF) {
+                m.abandon(p);
+                return;
+            }
+            while !p.at(EOF) {
+                p.bump_any();
+            }
+            m.complete(p, ERROR);
+        }
     }
 }