(display_mode_element): Detect cycles.

2 files changed, 13 insertions, 7 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index de2c7c30f44..d06faa3d711 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,7 @@
+2009-09-11  Andreas Schwab  <schwab@linux-m68k.org>
+
+        * xdisp.c (display_mode_element): Detect cycles.
+
 2009-09-11  Stefan Monnier  <monnier@iro.umontreal.ca>
 
         * keymap.c (where_is_internal): Don't erroneously return nil right after
diff --git a/src/xdisp.c b/src/xdisp.c
index 9108ab6bf72..58a077fe5f5 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -17750,14 +17750,10 @@ display_mode_element (it, depth, field_width, precision, elt, props, risky)
           }
         else if (STRINGP (car) || CONSP (car))
           {
-            register int limit = 5000;
-            /* Limit is to protect against circular lists.
-               The limit used to be 50, but if you use enough minor modes,
-               minor-mode-alist will easily grow past 50.  Circular lists
-               are rather unlikely, so it's better for the limit to be
-               "too large" rather than "too small".  */
+            Lisp_Object halftail = elt;
+            int len = 0;
+
             while (CONSP (elt)
-                   && --limit > 0
                    && (precision <= 0 || n < precision))
               {
                 n += display_mode_element (it, depth,
@@ -17769,6 +17765,12 @@ display_mode_element (it, depth, field_width, precision, elt, props, risky)
                                            precision - n, XCAR (elt),
                                            props, risky);
                 elt = XCDR (elt);
+                len++;
+                if ((len & 1) == 0)
+                  halftail = XCDR (halftail);
+                /* Check for cycle.  */
+                if (EQ (halftail, elt))
+                  break;
               }
           }
       }