qapi: Use predicate callback to determine visit filtering

Previously, qapi-types and qapi-visit filtered out implicit
objects during visit_object_type() by using 'info' (works since
implicit objects do not [yet] have associated info); meanwhile
qapi-introspect filtered out all schema types on the first pass
by returning a python type from visit_begin(), which was then
used at a distance in QAPISchema.visit() to do the filtering.

Rather than keeping these ad hoc approaches, add a new visitor
callback visit_needed() which returns False to skip a given
entity, and which defaults to True unless overridden.  Use the
new mechanism to simplify all three filtering visitors.

No change to the generated code.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1444710158-8723-2-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/scripts/qapi.py b/scripts/qapi.py
index 26cff3f05c..543b378d7e 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -811,6 +811,10 @@ class QAPISchemaVisitor(object):
     def visit_end(self):
         pass
 
+    def visit_needed(self, entity):
+        # Default to visiting everything
+        return True
+
     def visit_builtin_type(self, name, info, json_type):
         pass
 
@@ -1304,10 +1308,10 @@ class QAPISchema(object):
             ent.check(self)
 
     def visit(self, visitor):
-        ignore = visitor.visit_begin(self)
-        for name in sorted(self._entity_dict.keys()):
-            if not ignore or not isinstance(self._entity_dict[name], ignore):
-                self._entity_dict[name].visit(visitor)
+        visitor.visit_begin(self)
+        for (name, entity) in sorted(self._entity_dict.items()):
+            if visitor.visit_needed(entity):
+                entity.visit(visitor)
         visitor.visit_end()