From 04d8c47ded95adc93d1bc2082c9f8a39a9d4bb86 Mon Sep 17 00:00:00 2001
From: "Richard M. Stallman" <rms@gnu.org>
Date: Mon, 17 Jul 2006 21:00:58 +0000
Subject: [PATCH] (Vcommand_error_function): New variable. (syms_of_keyboard):
 Defvar it. (cmd_error_internal): Simplify, and handle
 Vcommand_error_function.

---
 src/keyboard.c | 69 +++++++++++++++++++++++++++-----------------------
 1 file changed, 38 insertions(+), 31 deletions(-)

diff --git a/src/keyboard.c b/src/keyboard.c
index 6bd9d754c60..4cbccb0b1a2 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -242,6 +242,9 @@ static int inhibit_local_menu_bar_menus;
 /* Nonzero means C-g should cause immediate error-signal.  */
 int immediate_quit;
 
+/* The user's hook function for outputting an error message.  */
+Lisp_Object Vcommand_error_function;
+
 /* The user's ERASE setting.  */
 Lisp_Object Vtty_erase_char;
 
@@ -1230,52 +1233,47 @@ cmd_error_internal (data, context)
      Lisp_Object data;
      char *context;
 {
-  Lisp_Object stream;
-  int kill_emacs_p = 0;
   struct frame *sf = SELECTED_FRAME ();
 
+  /* The immediate context is not interesting for Quits,
+     since they are asyncronous.  */
+  if (EQ (XCAR (data), Qquit))
+    Vsignaling_function = Qnil;
+
   Vquit_flag = Qnil;
   Vinhibit_quit = Qt;
-  clear_message (1, 0);
 
+  /* Use user's specified output function if any.  */
+  if (!NILP (Vcommand_error_function))
+    call3 (Vcommand_error_function, data,
+	   build_string (context ? context : ""),
+	   Vsignaling_function);
   /* If the window system or terminal frame hasn't been initialized
-     yet, or we're not interactive, it's best to dump this message out
-     to stderr and exit.  */
-  if (!sf->glyphs_initialized_p
-      /* This is the case of the frame dumped with Emacs, when we're
-	 running under a window system.  */
-      || (!NILP (Vwindow_system)
-	  && !inhibit_window_system
-	  && FRAME_TERMCAP_P (sf))
-      || noninteractive)
-    {
-      stream = Qexternal_debugging_output;
-      kill_emacs_p = 1;
+     yet, or we're not interactive, write the message to stderr and exit.  */
+  else if (!sf->glyphs_initialized_p
+	   /* This is the case of the frame dumped with Emacs, when we're
+	      running under a window system.  */
+	   || (!NILP (Vwindow_system)
+	       && !inhibit_window_system
+	       && FRAME_TERMCAP_P (sf))
+	   || noninteractive)
+    {
+      print_error_message (data, Qexternal_debugging_output,
+			   context, Vsignaling_function);
+      Fterpri (Qexternal_debugging_output);
+      Fkill_emacs (make_number (-1));
     }
   else
     {
+      clear_message (1, 0);
       Fdiscard_input ();
       message_log_maybe_newline ();
       bitch_at_user ();
-      stream = Qt;
-    }
-
-  /* The immediate context is not interesting for Quits,
-     since they are asyncronous.  */
-  if (EQ (XCAR (data), Qquit))
-    Vsignaling_function = Qnil;
 
-  print_error_message (data, stream, context, Vsignaling_function);
+      print_error_message (data, Qt, context, Vsignaling_function);
+    }
 
   Vsignaling_function = Qnil;
-
-  /* If the window system or terminal frame hasn't been initialized
-     yet, or we're in -batch mode, this error should cause Emacs to exit.  */
-  if (kill_emacs_p)
-    {
-      Fterpri (stream);
-      Fkill_emacs (make_number (-1));
-    }
 }
 
 Lisp_Object command_loop_1 ();
@@ -11484,6 +11482,15 @@ The value of that variable is passed to `quit-flag' and later causes a
 peculiar kind of quitting.  */);
   Vthrow_on_input = Qnil;
 
+  DEFVAR_LISP ("command-error-function", &Vcommand_error_function,
+	       doc: /* If non-nil, function to output error messages.
+The arguments are the error data, a list of the form
+ (SIGNALED-CONDITIONS . SIGNAL-DATA)
+such as just as `condition-case' would bind its variable to,
+the context (a string which normally goes at the start of the message),
+and the Lisp function within which the error was signaled.  */);
+  Vcommand_error_function = Qnil;
+
   DEFVAR_LISP ("enable-disabled-menus-and-buttons",
 	       &Venable_disabled_menus_and_buttons,
 	       doc: /* If non-nil, don't ignore events produced by disabled menu items and tool-bar.
-- 
2.39.2