WIP backtrace for errors outside expect

buttercup.el

@@ -2129,15 +2129,19 @@ ARGS according to `debugger'."
            ;; When the error occurs in the calling of one of the
            ;; wrapped expressions of an expect.
            (buttercup--wrapper-fun-p (cadr frame))
-           ;; TODO: When an error happens in code called outside an expect
+           ;; When an error happens in code called outside an expect
            ;; buttercup--update-with-funcall
            ;;  apply buttercup--funcall
            ;;   buttercup--funcall   -   sets debugger
            ;;    apply FUNCTION
            ;;     FUNCTION  -- spec body function
            ;;      condition-case   -- from buttercup-with-converted-ert-signals
-           ;;       progn           -- the same
+           ;;       (let ((buttercup--stackframe-marker 1))  -- the same
            ;;        ACTUAL CODE
+           (and (null (car frame))
+                (eq 'let (cadr frame))
+                (equal '((buttercup--stackframe-marker 1)) (caddr frame))
+                )
            ;; TODO: What about an error in a matcher?
            ;; TODO: What about :to-throw?
            ;; TODO: What about signals in before and after blocks?
@@ -2192,7 +2196,9 @@ Specifically, `ert-test-failed' is converted to
 `buttercup-pending'."
   (declare (indent 0))
   `(condition-case err
-       (progn ,@body)
+       (let ((buttercup--stackframe-marker 1))
+         (ignore buttercup--stackframe-marker)
+         ,@body)
      (ert-test-failed
       (buttercup-fail "%S" err))
      (ert-test-skipped