qapi: centralize the built-in module name definition

Use a constant to make it obvious we're referring to a very specific thing.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210201193747.2169670-11-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/schema.py

@@ -68,7 +68,7 @@ class QAPISchemaEntity:
 
     def _set_module(self, schema, info):
         assert self._checked
-        fname = info.fname if info else './builtin'
+        fname = info.fname if info else QAPISchemaModule.BUILTIN_MODULE_NAME
         self._module = schema.module_by_fname(fname)
         self._module.add_entity(self)
 
@@ -138,6 +138,9 @@ class QAPISchemaVisitor:
 
 
 class QAPISchemaModule:
+
+    BUILTIN_MODULE_NAME = './builtin'
+
     def __init__(self, name):
         self.name = name
         self._entity_list = []
@@ -160,14 +163,14 @@ class QAPISchemaModule:
         """
         return not cls.is_system_module(name)
 
-    @staticmethod
-    def is_builtin_module(name: str) -> bool:
+    @classmethod
+    def is_builtin_module(cls, name: str) -> bool:
         """
         The built-in module is a single System module for the built-in types.
 
         It is always "./builtin".
         """
-        return name == './builtin'
+        return name == cls.BUILTIN_MODULE_NAME
 
     def add_entity(self, ent):
         self._entity_list.append(ent)
@@ -853,7 +856,7 @@ class QAPISchema:
         self._entity_dict = {}
         self._module_dict = OrderedDict()
         self._schema_dir = os.path.dirname(fname)
-        self._make_module('./builtin')
+        self._make_module(QAPISchemaModule.BUILTIN_MODULE_NAME)
         self._make_module(fname)
         self._predefining = True
         self._def_predefineds()