(debug): Behave sensibly if pop-up-frames is set.

1 files changed, 13 insertions, 4 deletions

diff --git a/lisp/emacs-lisp/debug.el b/lisp/emacs-lisp/debug.el
index 150686ce4ce..68a26d8ebab 100644
--- a/lisp/emacs-lisp/debug.el
+++ b/lisp/emacs-lisp/debug.el
@@ -60,7 +60,7 @@ first will be printed into the backtrace buffer."
         (debug-on-error nil)
         (debug-on-quit nil)
         (debugger-buffer (let ((default-major-mode 'fundamental-mode))
-                           (generate-new-buffer "*Backtrace*")))
+                           (get-buffer-create "*Backtrace*")))
         (debugger-old-buffer (current-buffer))
         (debugger-step-after-exit nil)
         ;; Don't keep reading from an executing kbd macro!
@@ -136,9 +136,18 @@ first will be printed into the backtrace buffer."
                     (buffer-read-only t))
                 (message "")
                 (recursive-edit))))
-        ;; So that users do not try to execute debugger commands
-        ;;  in an invalid context
-        (kill-buffer debugger-buffer)
+        ;; Kill or at least neuter the backtrace buffer, so that users
+        ;; don't try to execute debugger commands in an invalid context.
+        (if (get-buffer-window debugger-buffer 'visible)
+            ;; Still visible despite the save-window-excursion?  Maybe it
+            ;; it's in a pop-up frame.  It would be annoying to delete and
+            ;; recreate it every time the debugger stops, so instead we'll
+            ;; erase it but leave it visible.
+            (save-excursion
+              (set-buffer debugger-buffer)
+              (erase-buffer)
+              (fundamental-mode))
+          (kill-buffer debugger-buffer))
         (store-match-data debugger-match-data)))
     ;; Put into effect the modified values of these variables
     ;; in case the user set them with the `e' command.