qapi: Implement deprecated-output=hide for QMP introspection

This policy suppresses deprecated bits in output, and thus permits
"testing the future".  Implement it for QMP command query-qmp-schema:
suppress information on deprecated commands, events and object type
members, i.e. anything that has the special feature flag "deprecated".

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210318155519.1224118-8-armbru@redhat.com>

monitor/qmp-cmds-control.c

@@ -134,6 +134,74 @@ CommandInfoList *qmp_query_commands(Error **errp)
     return list;
 }
 
+static void *split_off_generic_list(void *list,
+                                    bool (*splitp)(void *elt),
+                                    void **part)
+{
+    GenericList *keep = NULL, **keep_tailp = &keep;
+    GenericList *split = NULL, **split_tailp = &split;
+    GenericList *tail;
+
+    for (tail = list; tail; tail = tail->next) {
+        if (splitp(tail)) {
+            *split_tailp = tail;
+            split_tailp = &tail->next;
+        } else {
+            *keep_tailp = tail;
+            keep_tailp = &tail->next;
+        }
+    }
+
+    *keep_tailp = *split_tailp = NULL;
+    *part = split;
+    return keep;
+}
+
+static bool is_in(const char *s, strList *list)
+{
+    strList *tail;
+
+    for (tail = list; tail; tail = tail->next) {
+        if (!strcmp(tail->value, s)) {
+            return true;
+        }
+    }
+    return false;
+}
+
+static bool is_entity_deprecated(void *link)
+{
+    return is_in("deprecated", ((SchemaInfoList *)link)->value->features);
+}
+
+static bool is_member_deprecated(void *link)
+{
+    return is_in("deprecated",
+                 ((SchemaInfoObjectMemberList *)link)->value->features);
+}
+
+static SchemaInfoList *zap_deprecated(SchemaInfoList *schema)
+{
+    void *to_zap;
+    SchemaInfoList *tail;
+    SchemaInfo *ent;
+
+    schema = split_off_generic_list(schema, is_entity_deprecated, &to_zap);
+    qapi_free_SchemaInfoList(to_zap);
+
+    for (tail = schema; tail; tail = tail->next) {
+        ent = tail->value;
+        if (ent->meta_type == SCHEMA_META_TYPE_OBJECT) {
+            ent->u.object.members
+                = split_off_generic_list(ent->u.object.members,
+                                         is_member_deprecated, &to_zap);
+            qapi_free_SchemaInfoObjectMemberList(to_zap);
+        }
+    }
+
+    return schema;
+}
+
 SchemaInfoList *qmp_query_qmp_schema(Error **errp)
 {
     QObject *obj = qobject_from_qlit(&qmp_schema_qlit);
@@ -147,5 +215,8 @@ SchemaInfoList *qmp_query_qmp_schema(Error **errp)
     qobject_unref(obj);
     visit_free(v);
 
+    if (compat_policy.deprecated_output == COMPAT_POLICY_OUTPUT_HIDE) {
+        return zap_deprecated(schema);
+    }
     return schema;
 }