Check record size in pattern match

compiler.py

···
         if isinstance(pattern, Record):
             self._emit(f"if (!is_record({arg})) {{ goto {fallthrough}; }}")
             updates = {}
+            use_spread = False
             for key, pattern_value in pattern.data.items():
                 assert not isinstance(pattern_value, Spread), "record spread not yet supported"
                 key_idx = self.record_key(key)
                 record_value = self._mktemp(f"record_get({arg}, {key_idx})")
                 self._emit(f"if ({record_value} == NULL) {{ goto {fallthrough}; }}")
                 updates.update(self.try_match(env, record_value, pattern_value, fallthrough))
-            # TODO(max): Check that there are no other fields in the record,
-            # perhaps by length check
+            if not use_spread:
+                self._emit(f"if (record_num_fields({arg}) != {len(pattern.data)}) {{ goto {fallthrough}; }}")
             return updates
         raise NotImplementedError("try_match", pattern)
 

compiler_tests.py

···
     def test_match_record(self) -> None:
         self.assertEqual(self._run("f {a = 4, b = 5} . f = | {a = 1, b = 2} -> 3 | {a = 4, b = 5} -> 6"), "6\n")
 
+    def test_match_record_too_few_keys(self) -> None:
+        self.assertEqual(self._run("f {a = 4, b = 5} . f = | {a = _} -> 3 | {a = _, b = _} -> 6"), "6\n")
+
     @unittest.skip("TODO")
     def test_match_record_spread(self) -> None:
         self.assertEqual(self._run("f {a=1, b=2, c=3} . f = | {a=1, ...rest} -> rest"), "[5]\n")

runtime.c

···
   return result;
 }
 
+size_t record_num_fields(struct object* record) {
+  return as_record(record)->size;
+}
+
 void record_set(struct object* record, size_t index,
                 struct record_field field) {
   struct record* r = as_record(record);