Implement `debug-on-message'.

This allows tracking down what piece of code is outputting stuff in
the echo area.

* eval.c (call_debugger): Make the function non-static so that we
can call it from set_message.

* xdisp.c (set_message): Implement the new variable `debug-on-message'.
(syms_of_xdisp): Defvar it and `inhibit-debug-on-message'.

2 files changed, 9 insertions, 0 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index b0156e5ac7e..50f9853b7eb 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,7 @@
+2012-09-04  Lars Ingebrigtsen  <larsi@gnus.org>
+
+        * debugging.texi (Explicit Debug): Document `debug-on-message'.
+
 2012-09-02  Chong Yidong  <cyd@gnu.org>
 
         * windows.texi (Window Configurations): Recommend against using
diff --git a/doc/lispref/debugging.texi b/doc/lispref/debugging.texi
index 00e8d84e9b3..5aeff576d09 100644
--- a/doc/lispref/debugging.texi
+++ b/doc/lispref/debugging.texi
@@ -298,6 +298,11 @@ of @code{(debug)} isn't ignored, it will alter the execution of the
 program!)  The most common suitable places are inside a @code{progn} or
 an implicit @code{progn} (@pxref{Sequencing}).
 
+  If you don't know exactly where in the source code you want to put
+the debug statement, but you want to display a backtrace when a
+certain message is displayed, you can set @code{debug-on-message} to a
+regular expression matching the desired message.
+
 @node Using Debugger
 @subsection Using the Debugger