qapi/introspect.py: assert schema is not None

The introspect visitor is stateful, but expects that it will have a
schema to refer to. Add assertions that state this.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210216021809.134886-3-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/introspect.py

@@ -147,6 +147,8 @@ def _name(self, name):
         return self._name_map[name]
 
     def _use_type(self, typ):
+        assert self._schema is not None
+
         # Map the various integer types to plain int
         if typ.json_type() == 'int':
             typ = self._schema.lookup_type('int')
@@ -225,6 +227,8 @@ def visit_alternate_type(self, name, info, ifcond, features, variants):
     def visit_command(self, name, info, ifcond, features,
                       arg_type, ret_type, gen, success_response, boxed,
                       allow_oob, allow_preconfig, coroutine):
+        assert self._schema is not None
+
         arg_type = arg_type or self._schema.the_empty_object_type
         ret_type = ret_type or self._schema.the_empty_object_type
         obj = {'arg-type': self._use_type(arg_type),
@@ -234,6 +238,7 @@ def visit_command(self, name, info, ifcond, features,
         self._gen_tree(name, 'command', obj, ifcond, features)
 
     def visit_event(self, name, info, ifcond, features, arg_type, boxed):
+        assert self._schema is not None
         arg_type = arg_type or self._schema.the_empty_object_type
         self._gen_tree(name, 'event', {'arg-type': self._use_type(arg_type)},
                        ifcond, features)