qapi: Implement deprecated-output=hide for QMP events

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

No QMP event is deprecated right now.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210318155519.1224118-5-armbru@redhat.com>

scripts/qapi/events.py

@@ -79,6 +79,7 @@ def gen_param_var(typ: QAPISchemaObjectType) -> str:
 
 def gen_event_send(name: str,
                    arg_type: Optional[QAPISchemaObjectType],
+                   features: List[QAPISchemaFeature],
                    boxed: bool,
                    event_enum_name: str,
                    event_emit: str) -> str:
@@ -107,6 +108,14 @@ def gen_event_send(name: str,
         if not boxed:
             ret += gen_param_var(arg_type)
 
+    if 'deprecated' in [f.name for f in features]:
+        ret += mcgen('''
+
+    if (compat_policy.deprecated_output == COMPAT_POLICY_OUTPUT_HIDE) {
+        return;
+    }
+''')
+
     ret += mcgen('''
 
     qmp = qmp_event_build_dict("%(name)s");
@@ -176,6 +185,7 @@ def _begin_user_module(self, name: str) -> None:
 #include "%(prefix)sqapi-emit-events.h"
 #include "%(events)s.h"
 #include "%(visit)s.h"
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qdict.h"
 #include "qapi/qobject-output-visitor.h"
@@ -220,7 +230,7 @@ def visit_event(self,
                     boxed: bool) -> None:
         with ifcontext(ifcond, self._genh, self._genc):
             self._genh.add(gen_event_send_decl(name, arg_type, boxed))
-            self._genc.add(gen_event_send(name, arg_type, boxed,
+            self._genc.add(gen_event_send(name, arg_type, features, boxed,
                                           self._event_enum_name,
                                           self._event_emit_name))
         # Note: we generate the enum member regardless of @ifcond, to

tests/unit/test-qmp-event.c

@@ -14,6 +14,7 @@
 #include "qemu/osdep.h"
 
 #include "qemu-common.h"
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qbool.h"
 #include "qapi/qmp/qdict.h"
@@ -140,6 +141,24 @@ static void test_event_d(TestEventData *data,
     qobject_unref(data->expect);
 }
 
+static void test_event_deprecated(TestEventData *data, const void *unused)
+{
+    data->expect = qdict_from_jsonf_nofail("{ 'event': 'TEST-EVENT-FEATURES1' }");
+
+    memset(&compat_policy, 0, sizeof(compat_policy));
+
+    qapi_event_send_test_event_features1();
+    g_assert(data->emitted);
+
+    compat_policy.has_deprecated_output = true;
+    compat_policy.deprecated_output = COMPAT_POLICY_OUTPUT_HIDE;
+    data->emitted = false;
+    qapi_event_send_test_event_features1();
+    g_assert(!data->emitted);
+
+    qobject_unref(data->expect);
+}
+
 int main(int argc, char **argv)
 {
     g_test_init(&argc, &argv, NULL);
@@ -148,6 +167,7 @@ int main(int argc, char **argv)
     event_test_add("/event/event_b", test_event_b);
     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);
     g_test_run();
 
     return 0;