qapi-event: Simplify visit of non-implicit data

Commit 7ce106a documented why we don't generated a visit_type_FOO()
for implicit types; and therefore events with an anonymous type for
'data' have to open-code a visit.  Note that the open-coded visit in
qapi-event.c is slightly different from what is done in
qapi-visit.c for normal types, in part because we don't have to
check for *obj being NULL or free things on error.  But where the
type is not implicit, it is nicer to reuse the normal visit instead
of open-coding a duplicate.

At the moment, the only event with a non-implicit 'data' is in the
testsuite, where test-qapi-event.c changes as follows:

|@@ -155,6 +155,7 @@ void qapi_event_send___org_qemu_x_event(
|     __org_qemu_x_Struct param = {
|         __org_qemu_x_member1, (char *)__org_qemu_x_member2, has_q_wchar_t, q_wchar_t
|     };
|+    __org_qemu_x_Struct *arg = &param;
|
|     emit = qmp_event_get_func_emit();
|     if (!emit) {
|@@ -164,16 +165,7 @@ void qapi_event_send___org_qemu_x_event(
|     qmp = qmp_event_build_dict("__ORG.QEMU_X-EVENT");
|
|     v = qmp_output_visitor_new(&obj);
|-
|-    visit_start_struct(v, "__ORG.QEMU_X-EVENT", NULL, 0, &err);
|-    if (err) {
|-        goto out;
|-    }
|-    visit_type___org_qemu_x_Struct_members(v, &param, &err);
|-    if (!err) {
|-    if (!err) {
|-        visit_check_struct(v, &err);
|-    }
|-    visit_end_struct(v, NULL);
|+    visit_type___org_qemu_x_Struct(v, "__ORG.QEMU_X-EVENT", &arg, &err);
|     if (err) {
|         goto out;
|     }

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1468468228-27827-8-git-send-email-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi-event.py

@@ -49,6 +49,11 @@ def gen_param_var(typ):
 
     };
 ''')
+    if not typ.is_implicit():
+        ret += mcgen('''
+    %(c_name)s *arg = &param;
+''',
+                     c_name=typ.c_name())
     return ret
 
 
@@ -91,6 +96,14 @@ def gen_event_send(name, arg_type):
     if arg_type and not arg_type.is_empty():
         ret += mcgen('''
     v = qmp_output_visitor_new(&obj);
+''')
+        if not arg_type.is_implicit():
+            ret += mcgen('''
+    visit_type_%(c_name)s(v, "%(name)s", &arg, &err);
+''',
+                         name=name, c_name=arg_type.c_name())
+        else:
+            ret += mcgen('''
 
     visit_start_struct(v, "%(name)s", NULL, 0, &err);
     if (err) {
@@ -101,14 +114,16 @@ def gen_event_send(name, arg_type):
         visit_check_struct(v, &err);
     }
     visit_end_struct(v, NULL);
+''',
+                         name=name, c_name=arg_type.c_name())
+        ret += mcgen('''
     if (err) {
         goto out;
     }
 
     visit_complete(v, &obj);
     qdict_put_obj(qmp, "data", obj);
-''',
-                     name=name, c_name=arg_type.c_name())
+''')
 
     ret += mcgen('''
     emit(%(c_enum)s, qmp, &err);