Add function to load a user config file

This loads a config file first checking $XDG_CONFIG_HOME and if that
does not exist falls back to .config/mahogany/init.lisp.

It is adapted from the function in stumpwm.

lisp/main.lisp

@@ -33,33 +33,57 @@
     (new-view handle-new-view-event)
     (view-destroyed handle-view-destroyed-event)))
 
+(defun load-config-file (&optional (catch-errors t))
+  "Load the user's config file. Returns a values list: whether the file loaded (t if no
+rc files exist), the error if it didn't, and the config file that was
+loaded. When CATCH-ERRORS is nil, errors are left to be handled
+further up. "
+  (let* ((xdg-config
+           (probe-file (merge-pathnames #p"mahogany/init.lisp" (uiop:xdg-config-home))))
+	 (fallback-config
+	   (probe-file (merge-pathnames #p".config/mahogany/init.lisp" (user-homedir-pathname))))
+	 (config-file (or xdg-config fallback-config)))
+    (if config-file
+        (if catch-errors
+            (handler-case (load config-file)
+              (error (c) (values nil (format nil "~a" c) config-file))
+              (:no-error (&rest args) (declare (ignore args)) (values t nil config-file)))
+            (progn
+	      (log-string :debug (format nil "Found config file at ~a" config-file))
+              (load config-file)
+              (values t nil config-file)))
+	(progn
+	  (log-string :debug "Did not find config file")
+	  (values t nil nil)))))
+
 (defun run-server ()
   (disable-fpu-exceptions)
   (hrt:load-foreign-libraries)
   (log-init :level :trace)
   (sb-ext:enable-debugger)
+  (load-config-file)
   (cffi:with-foreign-objects ((output-callbacks '(:struct hrt-output-callbacks))
 			      (seat-callbacks '(:struct hrt-seat-callbacks))
 			      (view-callbacks '(:struct hrt-view-callbacks))
 			      (server '(:struct hrt-server)))
-    (init-callback-struct output-callbacks (:struct hrt-output-callbacks)
-      (output-added handle-new-output)
-      (output-removed handle-output-removed)
-      (output-mode-changed output-mode-change-callback))
-    (init-callback-struct seat-callbacks (:struct hrt-seat-callbacks)
-      (button-event cursor-callback)
-      (wheel-event cursor-callback)
-      (keyboard-keypress-event keyboard-callback))
-    (init-view-callbacks view-callbacks)
+			     (init-callback-struct output-callbacks (:struct hrt-output-callbacks)
+						   (output-added handle-new-output)
+						   (output-removed handle-output-removed)
+						   (output-mode-changed output-mode-change-callback))
+			     (init-callback-struct seat-callbacks (:struct hrt-seat-callbacks)
+						   (button-event cursor-callback)
+						   (wheel-event cursor-callback)
+						   (keyboard-keypress-event keyboard-callback))
+			     (init-view-callbacks view-callbacks)
 
-    (setf (mahogany-state-server *compositor-state*) server)
-    (log-string :debug "Initialized mahogany state")
-    (hrt-server-init server output-callbacks seat-callbacks view-callbacks 3)
-    (log-string :debug "Initialized heart state")
-    (unwind-protect
-	 (hrt-server-start server)
-      (log-string :debug "Cleaning up...")
-      (server-stop *compositor-state*)
-      (hrt-server-finish server)
-      (server-state-reset *compositor-state*)
-      (log-string :debug "Shutdown reached."))))
+			     (setf (mahogany-state-server *compositor-state*) server)
+			     (log-string :debug "Initialized mahogany state")
+			     (hrt-server-init server output-callbacks seat-callbacks view-callbacks 3)
+			     (log-string :debug "Initialized heart state")
+			     (unwind-protect
+				 (hrt-server-start server)
+			       (log-string :debug "Cleaning up...")
+			       (server-stop *compositor-state*)
+			       (hrt-server-finish server)
+			       (server-state-reset *compositor-state*)
+			       (log-string :debug "Shutdown reached."))))