(call_debugger): Take full care of extending stack limits

to make space for the debugger, and restore the change afterward.
Bind debug-on-error to nil.
(restore_stack_limits): New subroutine.
(Fsignal): Extend specpdl bound along with eval depth bound,
for calling edebug.  Don't do either one, for calling debugger.
(find_handler_clause): Don't bind debug-on-error here.
Don't unbind anything either.
Temporarily advance max_specpdl_size for calling
internal_with_output_to_temp_buffer.
(grow_specpdl): Don't alter max_specpdl_size before signaling an error.
(syms_of_eval) <max-specpdl-size>: Doc fix.

1 files changed, 48 insertions, 23 deletions

diff --git a/src/eval.c b/src/eval.c
index 8ad289fd51f..c33021da7b7 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -227,6 +227,18 @@ init_eval ()
   when_entered_debugger = -1;
 }
 
+/* unwind-protect function used by call_debugger.  */
+
+static Lisp_Object
+restore_stack_limits (data)
+     Lisp_Object data;
+{
+  max_specpdl_size = XINT (XCAR (data));
+  max_lisp_eval_depth = XINT (XCDR (data));
+}
+
+/* Call the Lisp debugger, giving it argument ARG.  */
+
 Lisp_Object
 call_debugger (arg)
      Lisp_Object arg;
@@ -234,12 +246,22 @@ call_debugger (arg)
   int debug_while_redisplaying;
   int count = SPECPDL_INDEX ();
   Lisp_Object val;
+  int old_max = max_specpdl_size;
 
-  if (lisp_eval_depth + 20 > max_lisp_eval_depth)
-    max_lisp_eval_depth = lisp_eval_depth + 20;
+  /* Temporarily bump up the stack limits,
+     so the debugger won't run out of stack.  */
 
-  if (specpdl_size + 40 > max_specpdl_size)
-    max_specpdl_size = specpdl_size + 40;
+  max_specpdl_size += 1;
+  record_unwind_protect (restore_stack_limits,
+                         Fcons (make_number (old_max),
+                                make_number (max_lisp_eval_depth)));
+  max_specpdl_size = old_max;
+
+  if (lisp_eval_depth + 40 > max_lisp_eval_depth)
+    max_lisp_eval_depth = lisp_eval_depth + 40;
+
+  if (SPECPDL_INDEX () + 100 > max_specpdl_size)
+    max_specpdl_size = SPECPDL_INDEX () + 100;
 
 #ifdef HAVE_X_WINDOWS
   if (display_hourglass_p)
@@ -256,6 +278,7 @@ call_debugger (arg)
   specbind (intern ("debugger-may-continue"),
             debug_while_redisplaying ? Qnil : Qt);
   specbind (Qinhibit_redisplay, Qnil);
+  specbind (Qdebug_on_error, Qnil);
 
 #if 0 /* Binding this prevents execution of Lisp code during
          redisplay, which necessarily leads to display problems.  */
@@ -1533,7 +1556,16 @@ See also the function `condition-case'.  */)
   /* This hook is used by edebug.  */
   if (! NILP (Vsignal_hook_function)
       && ! NILP (error_symbol))
-    call2 (Vsignal_hook_function, error_symbol, data);
+    {
+      /* Edebug takes care of restoring these variables when it exits.  */
+      if (lisp_eval_depth + 20 > max_lisp_eval_depth)
+        max_lisp_eval_depth = lisp_eval_depth + 20;
+
+      if (SPECPDL_INDEX () + 40 > max_specpdl_size)
+        max_specpdl_size = SPECPDL_INDEX () + 40;
+
+      call2 (Vsignal_hook_function, error_symbol, data);
+    }
 
   conditions = Fget (real_error_symbol, Qerror_conditions);
 
@@ -1555,12 +1587,6 @@ See also the function `condition-case'.  */)
     {
       register Lisp_Object clause;
 
-      if (lisp_eval_depth + 20 > max_lisp_eval_depth)
-        max_lisp_eval_depth = lisp_eval_depth + 20;
-
-      if (specpdl_size + 40 > max_specpdl_size)
-        max_specpdl_size = specpdl_size + 40;
-
       clause = find_handler_clause (handlerlist->handler, conditions,
                                     error_symbol, data, &debugger_value);
 
@@ -1673,7 +1699,11 @@ skip_debugger (conditions, data)
     = SIG is nil, and DATA is (SYMBOL . REST-OF-DATA).
        This is for memory-full errors only.
 
-   Store value returned from debugger into *DEBUGGER_VALUE_PTR.  */
+   Store value returned from debugger into *DEBUGGER_VALUE_PTR.
+
+   We need to increase max_specpdl_size temporarily around
+   anything we do that can push on the specpdl, so as not to get
+   a second error here in case we're handling specpdl overflow.  */
 
 static Lisp_Object
 find_handler_clause (handlers, conditions, sig, data, debugger_value_ptr)
@@ -1691,7 +1721,6 @@ find_handler_clause (handlers, conditions, sig, data, debugger_value_ptr)
       || !NILP (Vdebug_on_signal)) /* This says call debugger even if
                                       there is a handler.  */
     {
-      int count = SPECPDL_INDEX ();
       int debugger_called = 0;
       Lisp_Object sig_symbol, combined_data;
       /* This is set to 1 if we are handling a memory-full error,
@@ -1713,6 +1742,7 @@ find_handler_clause (handlers, conditions, sig, data, debugger_value_ptr)
 
       if (wants_debugger (Vstack_trace_on_error, conditions))
         {
+          max_specpdl_size++;
 #ifdef PROTOTYPES
           internal_with_output_to_temp_buffer ("*Backtrace*",
                                                (Lisp_Object (*) (Lisp_Object)) Fbacktrace,
@@ -1721,6 +1751,7 @@ find_handler_clause (handlers, conditions, sig, data, debugger_value_ptr)
           internal_with_output_to_temp_buffer ("*Backtrace*",
                                                Fbacktrace, Qnil);
 #endif
+          max_specpdl_size--;
         }
       if (! no_debugger
           && (EQ (sig_symbol, Qquit)
@@ -1729,7 +1760,6 @@ find_handler_clause (handlers, conditions, sig, data, debugger_value_ptr)
           && ! skip_debugger (conditions, combined_data)
           && when_entered_debugger < num_nonmacro_input_events)
         {
-          specbind (Qdebug_on_error, Qnil);
           *debugger_value_ptr
             = call_debugger (Fcons (Qerror,
                                     Fcons (combined_data, Qnil)));
@@ -1739,7 +1769,7 @@ find_handler_clause (handlers, conditions, sig, data, debugger_value_ptr)
       if (EQ (handlers, Qerror))
         {
           if (debugger_called)
-            return unbind_to (count, Qlambda);
+            return Qlambda;
           return Qt;
         }
     }
@@ -3019,13 +3049,8 @@ grow_specpdl ()
       if (max_specpdl_size < 400)
         max_specpdl_size = 400;
       if (specpdl_size >= max_specpdl_size)
-        {
-          if (!NILP (Vdebug_on_error))
-            /* Leave room for some specpdl in the debugger.  */
-            max_specpdl_size = specpdl_size + 100;
-          Fsignal (Qerror,
-                   Fcons (build_string ("Variable binding depth exceeds max-specpdl-size"), Qnil));
-        }
+        Fsignal (Qerror,
+                 Fcons (build_string ("Variable binding depth exceeds max-specpdl-size"), Qnil));
     }
   specpdl_size *= 2;
   if (specpdl_size > max_specpdl_size)
@@ -3333,7 +3358,7 @@ syms_of_eval ()
 {
   DEFVAR_INT ("max-specpdl-size", &max_specpdl_size,
               doc: /* *Limit on number of Lisp variable bindings & unwind-protects.
-If Lisp code tries to make more than this many at once,
+If Lisp code tries to increase the total number past this amount,
 an error is signaled.
 You can safely use a value considerably larger than the default value,
 if that proves inconveniently small.  However, if you increase it too far,