qapi: Implement deprecated-output=hide for QMP event data

This policy suppresses deprecated bits in output, and thus permits
"testing the future".  Implement it for QMP event data: suppress
deprecated members.

No QMP event data is deprecated right now.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210318155519.1224118-6-armbru@redhat.com>

scripts/qapi/events.py

@@ -126,7 +126,7 @@ def gen_event_send(name: str,
     if have_args:
         assert arg_type is not None
         ret += mcgen('''
-    v = qobject_output_visitor_new(&obj);
+    v = qobject_output_visitor_new_qmp(&obj);
 ''')
         if not arg_type.is_implicit():
             ret += mcgen('''
@@ -145,7 +145,11 @@ def gen_event_send(name: str,
         ret += mcgen('''
 
     visit_complete(v, &obj);
-    qdict_put_obj(qmp, "data", obj);
+    if (qdict_size(qobject_to(QDict, obj))) {
+        qdict_put_obj(qmp, "data", obj);
+    } else {
+        qobject_unref(obj);
+    }
 ''')
 
     ret += mcgen('''
@@ -188,7 +192,6 @@ def _begin_user_module(self, name: str) -> None:
 #include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qdict.h"
-#include "qapi/qobject-output-visitor.h"
 #include "qapi/qmp-event.h"
 
 ''',

tests/qapi-schema/qapi-schema-test.json

@@ -324,5 +324,8 @@
   'features': [ { 'name': 'feature1', 'if': [ 'defined(TEST_IF_COND_1)',
                                               'defined(TEST_IF_COND_2)'] } ] }
 
+{ 'event': 'TEST-EVENT-FEATURES0',
+  'data': 'FeatureStruct1' }
+
 { 'event': 'TEST-EVENT-FEATURES1',
   'features': [ 'deprecated' ] }

tests/qapi-schema/qapi-schema-test.out

@@ -440,6 +440,8 @@ command test-command-cond-features3 None -> None
     gen=True success_response=True boxed=False oob=False preconfig=False
     feature feature1
         if ['defined(TEST_IF_COND_1)', 'defined(TEST_IF_COND_2)']
+event TEST-EVENT-FEATURES0 FeatureStruct1
+    boxed=False
 event TEST-EVENT-FEATURES1 None
     boxed=False
     feature deprecated

tests/unit/test-qmp-event.c

@@ -159,6 +159,26 @@ static void test_event_deprecated(TestEventData *data, const void *unused)
     qobject_unref(data->expect);
 }
 
+static void test_event_deprecated_data(TestEventData *data, const void *unused)
+{
+    memset(&compat_policy, 0, sizeof(compat_policy));
+
+    data->expect = qdict_from_jsonf_nofail("{ 'event': 'TEST-EVENT-FEATURES0',"
+                                           " 'data': { 'foo': 42 } }");
+    qapi_event_send_test_event_features0(42);
+    g_assert(data->emitted);
+
+    qobject_unref(data->expect);
+
+    compat_policy.has_deprecated_output = true;
+    compat_policy.deprecated_output = COMPAT_POLICY_OUTPUT_HIDE;
+    data->expect = qdict_from_jsonf_nofail("{ 'event': 'TEST-EVENT-FEATURES0' }");
+    qapi_event_send_test_event_features0(42);
+    g_assert(data->emitted);
+
+    qobject_unref(data->expect);
+}
+
 int main(int argc, char **argv)
 {
     g_test_init(&argc, &argv, NULL);
@@ -168,6 +188,7 @@ int main(int argc, char **argv)
     event_test_add("/event/event_c", test_event_c);
     event_test_add("/event/event_d", test_event_d);
     event_test_add("/event/deprecated", test_event_deprecated);
+    event_test_add("/event/deprecated_data", test_event_deprecated_data);
     g_test_run();
 
     return 0;