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, 6 deletions

diff --git a/scripts/qapi.py b/scripts/qapi.py
index 7e6c396a1d..8bf41db4e2 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -1656,15 +1656,11 @@ def gen_visit_fields(members, prefix='', need_cast=False, skiperr=False):
     for memb in members:
         if memb.optional:
             ret += mcgen('''
-    visit_optional(v, &%(prefix)shas_%(c_name)s, "%(name)s", %(errp)s);
+    visit_optional(v, &%(prefix)shas_%(c_name)s, "%(name)s");
+    if (%(prefix)shas_%(c_name)s) {
 ''',
                          prefix=prefix, c_name=c_name(memb.name),
                          name=memb.name, errp=errparg)
-            ret += gen_err_check(skiperr=skiperr)
-            ret += mcgen('''
-    if (%(prefix)shas_%(c_name)s) {
-''',
-                         prefix=prefix, c_name=c_name(memb.name))
             push_indent()
 
         # Ugly: sometimes we need to cast away const