Set up debugger buffer earlier and fit window to it (Bug#32825)

* lisp/emacs-lisp/debug.el (debug): Set up debugger buffer
before displaying it and advise 'display-buffer' to fit the
window to it (Bug#32825).

1 files changed, 21 insertions, 19 deletions

diff --git a/lisp/emacs-lisp/debug.el b/lisp/emacs-lisp/debug.el
index b6b1f20675f..5c186f70197 100644
--- a/lisp/emacs-lisp/debug.el
+++ b/lisp/emacs-lisp/debug.el
@@ -236,12 +236,33 @@ first will be printed into the backtrace buffer."
                 ;; Place an extra debug-on-exit for macro's.
                 (when (eq 'lambda (car-safe (cadr (backtrace-frame 4))))
                   (backtrace-debug 5 t)))
+              (with-current-buffer debugger-buffer
+                (unless (derived-mode-p 'debugger-mode)
+                  (debugger-mode))
+                (debugger-setup-buffer debugger-args))
+              (when noninteractive
+                ;; If the backtrace is long, save the beginning
+                ;; and the end, but discard the middle.
+                (when (> (count-lines (point-min) (point-max))
+                         debugger-batch-max-lines)
+                  (goto-char (point-min))
+                  (forward-line (/ 2 debugger-batch-max-lines))
+                  (let ((middlestart (point)))
+                    (goto-char (point-max))
+                    (forward-line (- (/ 2 debugger-batch-max-lines)
+                                     debugger-batch-max-lines))
+                    (delete-region middlestart (point)))
+                  (insert "...\n"))
+                (goto-char (point-min))
+                (message "%s" (buffer-string))
+                (kill-emacs -1))
               (pop-to-buffer
                debugger-buffer
                `((display-buffer-reuse-window
                   display-buffer-in-previous-window
                   display-buffer-below-selected)
                  . ((window-min-height . 10)
+                    (window-height . fit-window-to-buffer)
                     ,@(when (and (window-live-p debugger-previous-window)
                                 (frame-visible-p
                                  (window-frame debugger-previous-window)))
@@ -258,25 +279,6 @@ first will be printed into the backtrace buffer."
                             (window-total-height debugger-window)))
                       (error nil)))
                 (setq debugger-previous-window debugger-window))
-              (unless (derived-mode-p 'debugger-mode)
-                (debugger-mode))
-              (debugger-setup-buffer debugger-args)
-              (when noninteractive
-                ;; If the backtrace is long, save the beginning
-                ;; and the end, but discard the middle.
-                (when (> (count-lines (point-min) (point-max))
-                         debugger-batch-max-lines)
-                  (goto-char (point-min))
-                  (forward-line (/ 2 debugger-batch-max-lines))
-                  (let ((middlestart (point)))
-                    (goto-char (point-max))
-                    (forward-line (- (/ 2 debugger-batch-max-lines)
-                                     debugger-batch-max-lines))
-                    (delete-region middlestart (point)))
-                  (insert "...\n"))
-                (goto-char (point-min))
-                (message "%s" (buffer-string))
-                (kill-emacs -1))
               (message "")
               (let ((standard-output nil)
                     (buffer-read-only t))