qapi/introspect.py: replace 'extra' dict with 'comment' argument

This is only used to pass in a dictionary with a comment already set, so
skip the runaround and just accept the (optional) comment.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210216021809.134886-8-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/introspect.py

@@ -10,6 +10,8 @@
 See the COPYING file in the top-level directory.
 """
 
+from typing import Optional
+
 from .common import (
     c_name,
     gen_endif,
@@ -24,11 +26,12 @@
 )
 
 
-def _make_tree(obj, ifcond, extra=None):
-    if extra is None:
-        extra = {}
+def _make_tree(obj, ifcond, comment=None):
+    extra = {}
     if ifcond:
         extra['if'] = ifcond
+    if comment:
+        extra['comment'] = comment
     return (obj, extra)
 
 
@@ -175,18 +178,18 @@ def _gen_features(features):
         return [_make_tree(f.name, f.ifcond) for f in features]
 
     def _gen_tree(self, name, mtype, obj, ifcond, features):
-        extra = None
+        comment: Optional[str] = None
         if mtype not in ('command', 'event', 'builtin', 'array'):
             if not self._unmask:
                 # Output a comment to make it easy to map masked names
                 # back to the source when reading the generated output.
-                extra = {'comment': '"%s" = %s' % (self._name(name), name)}
+                comment = f'"{self._name(name)}" = {name}'
             name = self._name(name)
         obj['name'] = name
         obj['meta-type'] = mtype
         if features:
             obj['features'] = self._gen_features(features)
-        self._trees.append(_make_tree(obj, ifcond, extra))
+        self._trees.append(_make_tree(obj, ifcond, comment))
 
     def _gen_member(self, member):
         obj = {'name': member.name, 'type': self._use_type(member.type)}