core: Parse module correctly when allow-unregistered-dialect is set

xdsl/parser/core.py

@@ -744,16 +744,23 @@ def _get_op_by_name(self, name: str) -> type[Operation]:
         Raises an error if the operation is not registered, and if unregistered
         dialects are not allowed.
         """
+        from xdsl.dialects import builtin
+
         op_type = self.ctx.get_optional_op(name)
-        if op_type is not None:
+
+        if op_type is not None and not issubclass(op_type, builtin.UnregisteredOp):
             return op_type
 
         for dialect_name in reversed(self._parser_state.dialect_stack):
-            op_type = self.ctx.get_optional_op(f"{dialect_name}.{name}")
-            if op_type is not None:
-                return op_type
-
-        self.raise_error(f"unregistered operation {name}!")
+            op_with_dialect_type = self.ctx.get_optional_op(f"{dialect_name}.{name}")
+            if op_with_dialect_type is not None and not issubclass(
+                op_with_dialect_type, builtin.UnregisteredOp
+            ):
+                return op_with_dialect_type
+
+        if op_type is None:
+            self.raise_error(f"unregistered operation {name}!")
+        return op_type
 
     def _parse_op_result(self) -> tuple[Span, int]:
         """