Don't crash on unbalanced unwinds in debug mode

* src/bytecode.c (exec_byte_code):
Restore the previous graceful error (instead of a hard crash) when the
bytecode doesn't unwind properly, but only when building with
debugging (NDEBUG not defined, checking enabled, or BYTE_CODE_SAFE
enabled).

1 files changed, 9 insertions, 2 deletions

diff --git a/src/bytecode.c b/src/bytecode.c
index 41455629cb9..0bca2546f7f 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -1588,10 +1588,17 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
 
  exit:
 
+#if BYTE_CODE_SAFE || !defined NDEBUG
+  if (SPECPDL_INDEX () != count)
+    {
+      /* Binds and unbinds are supposed to be compiled balanced.  */
+      if (SPECPDL_INDEX () > count)
+        unbind_to (count, Qnil);
+      error ("binding stack not balanced (serious byte compiler bug)");
+    }
+#endif
   /* The byte code should have been properly pinned.  */
   eassert (SDATA (bytestr) == bytestr_data);
-  /* Binds and unbinds are supposed to be compiled balanced.  */
-  eassert (SPECPDL_INDEX () == count);
 
   Lisp_Object result = TOP;
   SAFE_FREE ();