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+;;; exwm-debug.el --- Debugging helpers for EXWM  -*- lexical-binding: t -*-
+
+;; Copyright (C) 2018 Free Software Foundation, Inc.
+
+;; Author: Adrián Medraño Calvo <adrian@medranocalvo.com>
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This module collects functions that help in debugging EXWM.
+
+;;; Code:
+
+(eval-and-compile
+  (defvar exwm-debug-on nil "Non-nil to turn on debug for EXWM."))
+
+(defvar exwm-debug-buffer "*EXWM-DEBUG*" "Buffer to write debug messages to.")
+
+(defvar exwm-debug-backtrace-start-frame 5
+  "From which frame to start collecting backtraces.")
+
+(defun exwm-debug--call-stack ()
+  "Return the current call stack frames."
+  (let (frames frame
+        ;; No need to acount for our setq, while, let, ...
+        (index exwm-debug-backtrace-start-frame))
+    (while (setq frame (backtrace-frame index))
+      (push frame frames)
+      (cl-incf index))
+    (cl-remove-if-not 'car frames)))
+
+(defmacro exwm-debug--compile-time-function-name ()
+  "Get the name of outermost definition at expansion time."
+  (let* ((frame (cl-find-if
+		 (lambda (frame)
+		   (ignore-errors
+		     (let ((clause (car (cl-third frame))))
+		       (or (equal clause 'defalias)
+			   (equal clause 'cl-defmethod)))))
+		 (reverse (exwm-debug--call-stack))))
+	 (defn (cl-third frame))
+	 (deftype (car defn)))
+    (cl-case deftype
+      ((defalias) (symbol-name (cl-cadadr defn)))
+      ((cl-defmethod) (symbol-name (cadr defn)))
+      (t "<unknown function>"))))
+
+(defmacro exwm-debug--with-debug-buffer (&rest forms)
+  "Evaluate FORMS making sure `exwm-debug-buffer' is correctly updated."
+  `(with-current-buffer (get-buffer-create exwm-debug-buffer)
+     (let (windows-eob)
+       ;; Note windows whose point is at EOB.
+       (dolist (w (get-buffer-window-list exwm-debug-buffer t t))
+         (when (= (window-point w) (point-max))
+           (push w windows-eob)))
+       (save-excursion
+         (goto-char (point-max))
+         ,@forms)
+       ;; Restore point.
+       (dolist (w windows-eob)
+         (set-window-point w (point-max))))))
+
+(defun exwm-debug--message (format-string &rest objects)
+  "Print a message to `exwm-debug-buffer'.
+
+The FORMAT-STRING argument follows the speficies how to print each of
+the passed OBJECTS.  See `format' for details."
+  (exwm-debug--with-debug-buffer
+   (insert (apply #'format format-string objects))))
+
+(defmacro exwm-debug--backtrace ()
+  "Print a backtrace to the `exwm-debug-buffer'."
+  '(exwm-debug--with-debug-buffer
+    (let ((standard-output exwm-debug-buffer))
+      (backtrace))))
+
+(defmacro exwm-debug--backtrace-on-error (&rest forms)
+  "Evaluate FORMS.  Printing a backtrace if an error is signaled."
+  `(let ((debug-on-error t)
+         (debugger (lambda (&rest _) (exwm-debug--backtrace))))
+     ,@forms))
+
+(defun exwm-debug-clear ()
+  "Clear the debug buffer."
+  (interactive)
+  (exwm-debug--with-debug-buffer
+   (erase-buffer)))
+
+(defun exwm-debug-mark ()
+  "Insert a mark in the debug buffer."
+  (interactive)
+  (exwm-debug--with-debug-buffer
+   (insert "\n")))
+
+
+
+(provide 'exwm-debug)
+
+;;; exwm-debug.el ends here