qapi: Simplify visits of optional fields

None of the visitor callbacks would set an error when testing
if an optional field was present; make this part of the interface
contract by eliminating the errp argument.

The resulting generated code has a nice diff:

|-    visit_optional(v, &has_fdset_id, "fdset-id", &err);
|-    if (err) {
|-        goto out;
|-    }
|+    visit_optional(v, &has_fdset_id, "fdset-id");
|     if (has_fdset_id) {
|         visit_type_int(v, &fdset_id, "fdset-id", &err);
|         if (err) {
|             goto out;
|         }
|     }

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1449033659-25497-9-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index cee76bc..e07d6f9 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -73,11 +73,10 @@ void visit_end_union(Visitor *v, bool data_present, Error **errp)
     }
 }
 
-void visit_optional(Visitor *v, bool *present, const char *name,
-                    Error **errp)
+void visit_optional(Visitor *v, bool *present, const char *name)
 {
     if (v->optional) {
-        v->optional(v, present, name, errp);
+        v->optional(v, present, name);
     }
 }