qapi: fix error propagation

Don't overwrite / leak previously set errors.
Make traversal cope with missing mandatory sub-structs.
Don't try to end a container that could not be started.

v1->v2:
- unchanged

v2->v3:
- instead of examining, assert that we never overwrite errors with
  error_set()
- allow visitors to set a NULL struct pointer successfully, so traversal
  of incomplete objects can continue
- check for a NULL "obj" before accessing "(*obj)->has_XXX" (this is not a
  typo, "obj != NULL" implies "*obj != NULL" here)
- fix start_struct / end_struct balance for unions as well

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

1 files changed, 16 insertions, 8 deletions

diff --git a/tests/test-qmp-input-visitor.c b/tests/test-qmp-input-visitor.c
index c30fdc4e59..8f5a509582 100644
--- a/tests/test-qmp-input-visitor.c
+++ b/tests/test-qmp-input-visitor.c
@@ -151,14 +151,22 @@ typedef struct TestStruct
 static void visit_type_TestStruct(Visitor *v, TestStruct **obj,
                                   const char *name, Error **errp)
 {
-    visit_start_struct(v, (void **)obj, "TestStruct", name, sizeof(TestStruct),
-                       errp);
-
-    visit_type_int(v, &(*obj)->integer, "integer", errp);
-    visit_type_bool(v, &(*obj)->boolean, "boolean", errp);
-    visit_type_str(v, &(*obj)->string, "string", errp);
-
-    visit_end_struct(v, errp);
+    Error *err = NULL;
+    if (!error_is_set(errp)) {
+        visit_start_struct(v, (void **)obj, "TestStruct", name, sizeof(TestStruct),
+                           &err);
+        if (!err) {
+            visit_type_int(v, &(*obj)->integer, "integer", &err);
+            visit_type_bool(v, &(*obj)->boolean, "boolean", &err);
+            visit_type_str(v, &(*obj)->string, "string", &err);
+
+            /* Always call end_struct if start_struct succeeded.  */
+            error_propagate(errp, err);
+            err = NULL;
+            visit_end_struct(v, &err);
+        }
+        error_propagate(errp, err);
+    }
 }
 
 static void test_visitor_in_struct(TestInputVisitorData *data,