fixed rubout of Q-Register specifications

* This was a regression introduced by 257a0bf128e109442dce91c4aaa1d97fed17ad1a.
* The undo token that frees newly allocated teco_machine_qregspec_t must actually
  reset the pointer as well since any subsequent token, pushed by teco_undo_qregspec_own(),
  will expect a valid pointer.
* Could have been done via
  ctx->expectqreg = NULL;
  teco_undo_qregspec_own(ctx->expectqreg);
  but using a special clear function requires less memory and is easier to understand.
* Added test case. This wouldn't always crash, but should definitely show up in Valgrind.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/qreg.c b/src/qreg.c
index 1b97689..39406a2 100644
--- a/src/qreg.c
+++ b/src/qreg.c
@@ -1715,5 +1715,12 @@ teco_machine_qregspec_free(teco_machine_qregspec_t *ctx)
 	g_free(ctx);
 }
 
-TECO_DEFINE_UNDO_CALL(teco_machine_qregspec_free, teco_machine_qregspec_t *);
+static inline void
+teco_machine_qregspec_clear(teco_machine_qregspec_t **ctx)
+{
+	teco_machine_qregspec_free(*ctx);
+	*ctx = NULL;
+}
+
+TECO_DEFINE_UNDO_CALL(teco_machine_qregspec_clear, teco_machine_qregspec_t **);
 TECO_DEFINE_UNDO_OBJECT_OWN(qregspec, teco_machine_qregspec_t *, teco_machine_qregspec_free);