qapi/introspect.py: guard against ifcond/comment misuse

_tree_to_qlit is called recursively on dict values (isolated from their
keys); at such a point in generating output it is too late to apply an
ifcond. Similarly, comments do not necessarily have a "tidy" place they
can be printed in such a circumstance.

Forbid this usage by renaming "suppress_first_indent" to "dict_value" to
emphasize that indents are suppressed only for the benefit of dict
values; then add an assertion assuring we do not pass ifcond/comments
in this case.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210216021809.134886-6-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Comment wrapped to conform to PEP 8]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/introspect.py

@@ -34,7 +34,7 @@ def _make_tree(obj, ifcond, extra=None):
     return obj
 
 
-def _tree_to_qlit(obj, level=0, suppress_first_indent=False):
+def _tree_to_qlit(obj, level=0, dict_value=False):
 
     def indent(level):
         return level * 4 * ' '
@@ -43,6 +43,13 @@ def _tree_to_qlit(obj, level=0, suppress_first_indent=False):
         ifobj, extra = obj
         ifcond = extra.get('if')
         comment = extra.get('comment')
+
+        # NB: _tree_to_qlit is called recursively on the values of a
+        # key:value pair; those values can't be decorated with
+        # comments or conditionals.
+        msg = "dict values cannot have attached comments or if-conditionals."
+        assert not dict_value, msg
+
         ret = ''
         if comment:
             ret += indent(level) + '/* %s */\n' % comment
@@ -54,7 +61,7 @@ def _tree_to_qlit(obj, level=0, suppress_first_indent=False):
         return ret
 
     ret = ''
-    if not suppress_first_indent:
+    if not dict_value:
         ret += indent(level)
     if obj is None:
         ret += 'QLIT_QNULL'