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, 1 insertions, 1 deletions

diff --git a/error.h b/error.h
index 45ff6c1ffe..3d9d96def0 100644
--- a/error.h
+++ b/error.h
@@ -57,7 +57,7 @@ void error_set_field(Error *err, const char *field, const char *value);
 /**
  * Propagate an error to an indirect pointer to an error.  This function will
  * always transfer ownership of the error reference and handles the case where
- * dst_err is NULL correctly.
+ * dst_err is NULL correctly.  Errors after the first are discarded.
  */
 void error_propagate(Error **dst_err, Error *local_err);