qapi: Simplify error cleanup in test-qmp-*

We have several tests that perform multiple sub-actions that are
expected to fail.  Asserting that an error occurred, then clearing
it up to prepare for the next action, turned into enough
boilerplate that it was sometimes forgotten (for example, a number
of tests added to test-qmp-input-visitor.c in d88f5fd leaked err).
Worse, if an error is not reset to NULL, we risk invalidating
later use of that error (passing a non-NULL err into a function
is generally a bad idea).  Encapsulate the boilerplate into a
single helper function error_free_or_abort(), and consistently
use it.

The new function is added into error.c for use everywhere,
although it is anticipated that testsuites will be the main
client.

Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/qapi/error.h b/include/qapi/error.h
index c69dddb..4d42cdc 100644
--- a/include/qapi/error.h
+++ b/include/qapi/error.h
@@ -30,6 +30,10 @@
  * Handle an error without reporting it (just for completeness):
  *     error_free(err);
  *
+ * Assert that an expected error occurred, but clean it up without
+ * reporting it (primarily useful in testsuites):
+ *     error_free_or_abort(&err);
+ *
  * Pass an existing error to the caller:
  *     error_propagate(errp, err);
  * where Error **errp is a parameter, by convention the last one.
@@ -190,6 +194,11 @@ Error *error_copy(const Error *err);
 void error_free(Error *err);
 
 /*
+ * Convenience function to assert that *@errp is set, then silently free it.
+ */
+void error_free_or_abort(Error **errp);
+
+/*
  * Convenience function to error_report() and free @err.
  */
 void error_report_err(Error *);