Let the debugger continue to the normal handler.

* src/eval.c (maybe_call_debugger): Declare before new use.
(find_handler_clause): Don't call debugger any more.
Ignore Vstack_trace_on_error.
Use XCAR/XCDR.
(syms_of_eval): Remove Vstack_trace_on_error.
(Fsignal): Only modify handlerlist when we know we need to do it.
Call the debugger when necessary.
* src/globals.h (Vstack_trace_on_error): Remove.

Fixes: debbugs:7825

5 files changed, 66 insertions, 116 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 0a12a122d27..da9f1aa3ac1 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -692,6 +692,11 @@ sc.el, x-menu.el, rnews.el, rnewspost.el
 
 * Lisp changes in Emacs 24.1
 
+** Removed the stack-trace-on-error variable.
+Also the debugger can now "continue" from an error, which means it will jump
+to the error handler as if the debugger had not been invoked instead of
+jumping all the way to the top-level.
+
 ** New function `read-char-choice' reads a restricted set of characters,
 discarding any inputs not inside the set.
 
diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index f89a5b37ff0..d2d99ee64fb 100644
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -166,12 +166,6 @@ Leaving \"Default\" unchecked is equivalent with specifying a default of
              (max-mini-window-height limits
                                      (choice (const :tag "quarter screen" nil)
                                              number) "23.1")
-             (stack-trace-on-error debug
-                                   (choice (const :tag "off")
-                                           (repeat :menu-tag "When"
-                                                   :value (nil)
-                                                   (symbol :format "%v"))
-                                           (const :tag "always" t)))
              (debug-on-error debug
                              (choice (const :tag "off")
                                      (repeat :menu-tag "When"
diff --git a/src/ChangeLog b/src/ChangeLog
index 2041b5bb45c..62782e63eef 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,15 @@
+2011-01-26  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+        Let the debugger continue to the normal handler (bug#7825).
+        * eval.c (maybe_call_debugger): Declare before new use.
+        (find_handler_clause): Don't call debugger any more.
+        Ignore Vstack_trace_on_error.
+        Use XCAR/XCDR.
+        (syms_of_eval): Remove Vstack_trace_on_error.
+        (Fsignal): Only modify handlerlist when we know we need to do it.
+        Call the debugger when necessary.
+        * globals.h (Vstack_trace_on_error): Remove.
+
 2011-01-26  Chong Yidong  <cyd@stupidchicken.com>
 
         * font.c (font_parse_fcname): Rewrite GTK font name parser.
diff --git a/src/eval.c b/src/eval.c
index 709366717da..d0effc755a2 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1557,6 +1557,8 @@ internal_condition_case_n (Lisp_Object (*bfun) (int, Lisp_Object*),
 
 static Lisp_Object find_handler_clause (Lisp_Object, Lisp_Object,
                                         Lisp_Object, Lisp_Object);
+static int maybe_call_debugger (Lisp_Object conditions, Lisp_Object sig,
+                                Lisp_Object data);
 
 DEFUN ("signal", Fsignal, Ssignal, 2, 2, 0,
        doc: /* Signal an error.  Args are ERROR-SYMBOL and associated DATA.
@@ -1577,10 +1579,12 @@ See also the function `condition-case'.  */)
   /* When memory is full, ERROR-SYMBOL is nil,
      and DATA is (REAL-ERROR-SYMBOL . REAL-DATA).
      That is a special case--don't do this in other situations.  */
-  register struct handler *allhandlers = handlerlist;
   Lisp_Object conditions;
   Lisp_Object string;
-  Lisp_Object real_error_symbol;
+  Lisp_Object real_error_symbol
+    = (NILP (error_symbol) ? Fcar (data) : error_symbol);
+  register Lisp_Object clause = Qnil;
+  struct handler *h;
   struct backtrace *bp;
 
   immediate_quit = handling_signal = 0;
@@ -1588,11 +1592,6 @@ See also the function `condition-case'.  */)
   if (gc_in_progress || waiting_for_input)
     abort ();
 
-  if (NILP (error_symbol))
-    real_error_symbol = Fcar (data);
-  else
-    real_error_symbol = error_symbol;
-
 #if 0 /* rms: I don't know why this was here,
          but it is surely wrong for an error that is handled.  */
 #ifdef HAVE_WINDOW_SYSTEM
@@ -1631,49 +1630,49 @@ See also the function `condition-case'.  */)
         Vsignaling_function = *bp->function;
     }
 
-  for (; handlerlist; handlerlist = handlerlist->next)
+  for (h = handlerlist; h; h = h->next)
     {
-      register Lisp_Object clause;
-
-      clause = find_handler_clause (handlerlist->handler, conditions,
+      clause = find_handler_clause (h->handler, conditions,
                                     error_symbol, data);
-
-      if (EQ (clause, Qlambda))
-        {
-          /* We can't return values to code which signaled an error, but we
-             can continue code which has signaled a quit.  */
-          if (EQ (real_error_symbol, Qquit))
-            return Qnil;
-          else
-            error ("Cannot return from the debugger in an error");
-        }
-
       if (!NILP (clause))
-        {
-          Lisp_Object unwind_data;
-          struct handler *h = handlerlist;
-
-          handlerlist = allhandlers;
-
-          if (NILP (error_symbol))
-            unwind_data = data;
-          else
-            unwind_data = Fcons (error_symbol, data);
-          h->chosen_clause = clause;
-          unwind_to_catch (h->tag, unwind_data);
-        }
+        break;
     }
+          
+  if (/* Don't run the debugger for a memory-full error.
+         (There is no room in memory to do that!) */
+      !NILP (error_symbol)
+      && (!NILP (Vdebug_on_signal)
+          /* If no handler is present now, try to run the debugger.  */
+          || NILP (clause)
+          /* Special handler that means "print a message and run debugger
+             if requested".  */
+          || EQ (h->handler, Qerror)))
+    {
+      int debugger_called
+        = maybe_call_debugger (conditions, error_symbol, data);
+      /* We can't return values to code which signaled an error, but we
+         can continue code which has signaled a quit.  */
+      if (debugger_called && EQ (real_error_symbol, Qquit))
+        return Qnil;
+    }      
 
-  handlerlist = allhandlers;
-  /* If no handler is present now, try to run the debugger,
-     and if that fails, throw to top level.  */
-  find_handler_clause (Qerror, conditions, error_symbol, data);
-  if (catchlist != 0)
-    Fthrow (Qtop_level, Qt);
+  if (!NILP (clause))
+    {
+      Lisp_Object unwind_data
+        = (NILP (error_symbol) ? data : Fcons (error_symbol, data));
+      
+      h->chosen_clause = clause;
+      unwind_to_catch (h->tag, unwind_data);
+    }
+  else
+    {
+      if (catchlist != 0)
+        Fthrow (Qtop_level, Qt);
+    }
 
   if (! NILP (error_symbol))
     data = Fcons (error_symbol, data);
-
+      
   string = Ferror_message_string (data);
   fatal ("%s", SDATA (string), 0);
 }
@@ -1848,63 +1847,24 @@ find_handler_clause (Lisp_Object handlers, Lisp_Object conditions,
                      Lisp_Object sig, Lisp_Object data)
 {
   register Lisp_Object h;
-  register Lisp_Object tem;
-  int debugger_called = 0;
-  int debugger_considered = 0;
 
   /* t is used by handlers for all conditions, set up by C code.  */
   if (EQ (handlers, Qt))
     return Qt;
 
-  /* Don't run the debugger for a memory-full error.
-     (There is no room in memory to do that!)  */
-  if (NILP (sig))
-    debugger_considered = 1;
-
   /* error is used similarly, but means print an error message
      and run the debugger if that is enabled.  */
-  if (EQ (handlers, Qerror)
-      || !NILP (Vdebug_on_signal)) /* This says call debugger even if
-                                      there is a handler.  */
-    {
-      if (!NILP (sig) && wants_debugger (Vstack_trace_on_error, conditions))
-        {
-          max_lisp_eval_depth += 15;
-          max_specpdl_size++;
-          if (noninteractive)
-            Fbacktrace ();
-          else
-            internal_with_output_to_temp_buffer
-              ("*Backtrace*",
-               (Lisp_Object (*) (Lisp_Object)) Fbacktrace,
-               Qnil);
-          max_specpdl_size--;
-          max_lisp_eval_depth -= 15;
-        }
-
-      if (!debugger_considered)
-        {
-          debugger_considered = 1;
-          debugger_called = maybe_call_debugger (conditions, sig, data);
-        }
-
-      /* If there is no handler, return saying whether we ran the debugger.  */
-      if (EQ (handlers, Qerror))
-        {
-          if (debugger_called)
-            return Qlambda;
-          return Qt;
-        }
-    }
+  if (EQ (handlers, Qerror))
+    return Qt;
 
-  for (h = handlers; CONSP (h); h = Fcdr (h))
+  for (h = handlers; CONSP (h); h = XCDR (h))
     {
-      Lisp_Object handler, condit;
+      Lisp_Object handler = XCAR (h);
+      Lisp_Object condit, tem;
 
-      handler = Fcar (h);
       if (!CONSP (handler))
         continue;
-      condit = Fcar (handler);
+      condit = XCAR (handler);
       /* Handle a single condition name in handler HANDLER.  */
       if (SYMBOLP (condit))
         {
@@ -1918,15 +1878,9 @@ find_handler_clause (Lisp_Object handlers, Lisp_Object conditions,
           Lisp_Object tail;
           for (tail = condit; CONSP (tail); tail = XCDR (tail))
             {
-              tem = Fmemq (Fcar (tail), conditions);
+              tem = Fmemq (XCAR (tail), conditions);
               if (!NILP (tem))
-                {
-                  /* This handler is going to apply.
-                     Does it allow the debugger to run first?  */
-                  if (! debugger_considered && !NILP (Fmemq (Qdebug, condit)))
-                    maybe_call_debugger (conditions, sig, data);
-                  return handler;
-                }
+                return handler;
             }
         }
     }
@@ -1943,7 +1897,6 @@ verror (const char *m, va_list ap)
   EMACS_INT size = 200;
   int mlen;
   char *buffer = buf;
-  char *args[3];
   int allocated = 0;
   Lisp_Object string;
 
@@ -3523,14 +3476,6 @@ before making `inhibit-quit' nil.  */);
   Qdebug = intern_c_string ("debug");
   staticpro (&Qdebug);
 
-  DEFVAR_LISP ("stack-trace-on-error", Vstack_trace_on_error,
-               doc: /* *Non-nil means errors display a backtrace buffer.
-More precisely, this happens for any error that is handled
-by the editor command loop.
-If the value is a list, an error only means to display a backtrace
-if one of its condition symbols appears in the list.  */);
-  Vstack_trace_on_error = Qnil;
-
   DEFVAR_LISP ("debug-on-error", Vdebug_on_error,
                doc: /* *Non-nil means enter debugger if an error is signaled.
 Does not apply to errors handled by `condition-case' or those
diff --git a/src/globals.h b/src/globals.h
index 3d7203b875a..5dc2d540409 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -434,10 +434,6 @@ struct emacs_globals
      continue the interrupted redisplay. */
   int f_debugger_may_continue;
 
-  /* List of conditions (non-nil atom means all) which cause a backtrace
-     if an error is handled by the command loop's error handler.  */
-  Lisp_Object f_Vstack_trace_on_error;
-
   /* List of conditions (non-nil atom means all) which enter the debugger
      if an error is handled by the command loop's error handler.  */
   Lisp_Object f_Vdebug_on_error;
@@ -2326,8 +2322,6 @@ extern struct emacs_globals globals;
     globals.f_Vsource_directory
 #define Vspecial_event_map \
     globals.f_Vspecial_event_map
-#define Vstack_trace_on_error \
-    globals.f_Vstack_trace_on_error
 #define Vstandard_display_table \
     globals.f_Vstandard_display_table
 #define Vstandard_input \