Last portion of fix for bug #16051 with redisplay loops.

 src/xdisp.c (redisplay_tool_bar): Modify the tool-bar-lines frame parameter
 only when the new size is different from the old one, and the new
 size can be achieved given the frame height.

2 files changed, 30 insertions, 10 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index e1df65bbfe8..818ff2784be 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -5,6 +5,9 @@
         redisplay_tool_bar does.  Improve and fix commentary.
         (hscroll_window_tree): Don't assume w->cursor.vpos is within the
         limits of the glyph matrices.  (Bug#16051)
+        (redisplay_tool_bar): Modify the tool-bar-lines frame parameter
+        only when the new size is different from the old one, and the new
+        size can be achieved given the frame height.
 
 2013-12-23  Jan Djärv  <jan.h.d@swipnet.se>
 
diff --git a/src/xdisp.c b/src/xdisp.c
index 9a3c27fc6ae..1c157c7be0a 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -12289,18 +12289,35 @@ redisplay_tool_bar (struct frame *f)
 
           if (change_height_p)
             {
+              /* Current size of the tool-bar window in canonical line
+                 units.  */
+              int old_lines = WINDOW_TOTAL_LINES (w);
+              /* Required size of the tool-bar window in canonical
+                 line units. */
               int new_lines = ((new_height + FRAME_LINE_HEIGHT (f) - 1)
                                / FRAME_LINE_HEIGHT (f));
-
-              XSETFRAME (frame, f);
-              Fmodify_frame_parameters (frame,
-                                        list1 (Fcons (Qtool_bar_lines,
-                                                      make_number (new_lines))));
-              /* Always do that now.  */
-              clear_glyph_matrix (w->desired_matrix);
-              f->n_tool_bar_rows = nrows;
-              f->fonts_changed = 1;
-              return 1;
+              /* Maximum size of the tool-bar window in canonical line
+                 units that this frame can allow. */
+              int max_lines =
+                WINDOW_TOTAL_LINES (XWINDOW (FRAME_ROOT_WINDOW (f))) - 1;
+
+              /* Don't try to change the tool-bar window size and set
+                 the fonts_changed flag unless really necessary.  That
+                 flag causes redisplay to give up and retry
+                 redisplaying the frame from scratch, so setting it
+                 unnecessarily can lead to nasty redisplay loops.  */
+              if (new_lines <= max_lines
+                  && eabs (new_lines - old_lines) >= 1)
+                {
+                  XSETFRAME (frame, f);
+                  Fmodify_frame_parameters (frame,
+                                            list1 (Fcons (Qtool_bar_lines,
+                                                          make_number (new_lines))));
+                  clear_glyph_matrix (w->desired_matrix);
+                  f->n_tool_bar_rows = nrows;
+                  f->fonts_changed = 1;
+                  return 1;
+                }
             }
         }
     }