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, 2 insertions, 0 deletions

diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt
index ad11767a2f..cccb11e562 100644
--- a/docs/qapi-code-gen.txt
+++ b/docs/qapi-code-gen.txt
@@ -220,6 +220,8 @@ Example:
     #endif
     mdroth@illuin:~/w/qemu2.git$
 
+(The actual structure of the visit_type_* functions is a bit more complex
+in order to propagate errors correctly and avoid leaking memory).
 
 === scripts/qapi-commands.py ===