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, 4 insertions, 6 deletions

diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 705eca90aa..d41595eaa1 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -39,9 +39,8 @@ void visit_start_struct(Visitor *v, void **obj, const char *kind,
 
 void visit_end_struct(Visitor *v, Error **errp)
 {
-    if (!error_is_set(errp)) {
-        v->end_struct(v, errp);
-    }
+    assert(!error_is_set(errp));
+    v->end_struct(v, errp);
 }
 
 void visit_start_list(Visitor *v, const char *name, Error **errp)
@@ -62,9 +61,8 @@ GenericList *visit_next_list(Visitor *v, GenericList **list, Error **errp)
 
 void visit_end_list(Visitor *v, Error **errp)
 {
-    if (!error_is_set(errp)) {
-        v->end_list(v, errp);
-    }
+    assert(!error_is_set(errp));
+    v->end_list(v, errp);
 }
 
 void visit_start_optional(Visitor *v, bool *present, const char *name,