X-Git-Url: https://code.delx.au/gnu-emacs/blobdiff_plain/67ab0163d67fbfeb41c37c8a259f27eeef965520..bc81e2c4e885787603da3e0314d6ea45a43f7862:/lisp/emacs-lisp/debug.el

diff --git a/lisp/emacs-lisp/debug.el b/lisp/emacs-lisp/debug.el
index 88633eaaa4..157749500e 100644
--- a/lisp/emacs-lisp/debug.el
+++ b/lisp/emacs-lisp/debug.el
@@ -102,7 +102,7 @@ and `debugger-reenable' to temporarily disable debug-on-entry.")
 (setq debugger 'debug)
 ;;;###autoload
 (defun debug (&rest debugger-args)
-  "Enter debugger.  To return, type \\<debugger-mode-map>`\\[debugger-continue]'.
+  "Enter debugger.  \\<debugger-mode-map>`\\[debugger-continue]' returns from the debugger.
 Arguments are mainly for use when this is called from the internals
 of the evaluator.
 
@@ -118,6 +118,10 @@ first will be printed into the backtrace buffer."
     (let (debugger-value
 	  (debug-on-error nil)
 	  (debug-on-quit nil)
+	  (debugger-previous-state
+           (if (get-buffer "*Backtrace*")
+               (with-current-buffer (get-buffer "*Backtrace*")
+                 (list major-mode (buffer-string)))))
 	  (debugger-buffer (get-buffer-create "*Backtrace*"))
 	  (debugger-old-buffer (current-buffer))
 	  (debugger-step-after-exit nil)
@@ -214,8 +218,6 @@ first will be printed into the backtrace buffer."
 	      ;; recreate it every time the debugger stops, so instead we'll
 	      ;; erase it (and maybe hide it) but keep it alive.
 	      (with-current-buffer debugger-buffer
-		(erase-buffer)
-		(fundamental-mode)
 		(with-selected-window (get-buffer-window debugger-buffer 0)
                   (when (and (window-dedicated-p (selected-window))
                              (not debugger-will-be-back))
@@ -232,7 +234,18 @@ first will be printed into the backtrace buffer."
                     ;; to be left at the top-level, still working on how
                     ;; best to do that.
                     (bury-buffer))))
-	    (kill-buffer debugger-buffer))
+            (unless debugger-previous-state
+              (kill-buffer debugger-buffer)))
+          ;; Restore the previous state of the debugger-buffer, in case we were
+          ;; in a recursive invocation of the debugger.
+          (when (buffer-live-p debugger-buffer)
+            (with-current-buffer debugger-buffer
+              (let ((inhibit-read-only t))
+                (erase-buffer)
+                (if (null debugger-previous-state)
+                    (fundamental-mode)
+                  (insert (nth 1 debugger-previous-state))
+                  (funcall (nth 0 debugger-previous-state))))))
 	  (with-timeout-unsuspend debugger-with-timeout-suspend)
 	  (set-match-data debugger-outer-match-data)))
       ;; Put into effect the modified values of these variables