A better fix for bug#21739

* src/buffer.c (set_update_modelines_for_buf): New function.
(Fkill_buffer): Use it to set the global variable
update_mode_lines if the killed buffer was displayed in some
window.  Don't set windows_or_buffers_changed.  This is a better
fix for bug#21739 than the previous fix, since it will cause only
redisplay of mode lines, not of entire windows, but will still
catch attention of x_consider_frame_title in xdisp.c, which
redraws the frame title.

1 files changed, 41 insertions, 11 deletions

diff --git a/src/buffer.c b/src/buffer.c
index aff80bce4c9..84768767c6b 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1611,6 +1611,19 @@ compact_buffer (struct buffer *buffer)
     }
 }
 
+/* Set the global update_mode_lines variable non-zero if the buffer
+   was displayed in some window.  This is needed to catch the
+   attention of redisplay to changes that might require redisplay of
+   the frame title (which uses the same variables as mode lines) when
+   the buffer object cannot be used for recording that fact, e.g. if
+   the buffer is killed.  */
+static void
+set_update_modelines_for_buf (bool disp)
+{
+  if (disp)
+    update_mode_lines = 42;
+}
+
 DEFUN ("kill-buffer", Fkill_buffer, Skill_buffer, 0, 1, "bKill buffer: ",
        doc: /* Kill the buffer specified by BUFFER-OR-NAME.
 The argument may be a buffer or the name of an existing buffer.
@@ -1633,6 +1646,7 @@ cleaning up all windows currently displaying the buffer to be killed. */)
   struct buffer *b;
   Lisp_Object tem;
   struct Lisp_Marker *m;
+  bool buffer_was_displayed = false;
 
   if (NILP (buffer_or_name))
     buffer = Fcurrent_buffer ();
@@ -1647,6 +1661,8 @@ cleaning up all windows currently displaying the buffer to be killed. */)
   if (!BUFFER_LIVE_P (b))
     return Qnil;
 
+  buffer_was_displayed = buffer_window_count (b);
+
   /* Run hooks with the buffer to be killed the current buffer.  */
   {
     ptrdiff_t count = SPECPDL_INDEX ();
@@ -1673,7 +1689,10 @@ cleaning up all windows currently displaying the buffer to be killed. */)
 
     /* If the hooks have killed the buffer, exit now.  */
     if (!BUFFER_LIVE_P (b))
-      return unbind_to (count, Qt);
+      {
+        set_update_modelines_for_buf (buffer_was_displayed);
+        return unbind_to (count, Qt);
+      }
 
     /* Then run the hooks.  */
     run_hook (Qkill_buffer_hook);
@@ -1682,7 +1701,10 @@ cleaning up all windows currently displaying the buffer to be killed. */)
 
   /* If the hooks have killed the buffer, exit now.  */
   if (!BUFFER_LIVE_P (b))
-    return Qt;
+    {
+      set_update_modelines_for_buf (buffer_was_displayed);
+      return Qt;
+    }
 
   /* We have no more questions to ask.  Verify that it is valid
      to kill the buffer.  This must be done after the questions
@@ -1710,7 +1732,10 @@ cleaning up all windows currently displaying the buffer to be killed. */)
 
       /* Exit if we now have killed the base buffer (Bug#11665).  */
       if (!BUFFER_LIVE_P (b))
-        return Qt;
+        {
+          set_update_modelines_for_buf (buffer_was_displayed);
+          return Qt;
+        }
     }
 
   /* Run replace_buffer_in_windows before making another buffer current
@@ -1721,7 +1746,10 @@ cleaning up all windows currently displaying the buffer to be killed. */)
 
   /* Exit if replacing the buffer in windows has killed our buffer.  */
   if (!BUFFER_LIVE_P (b))
-    return Qt;
+    {
+      set_update_modelines_for_buf (buffer_was_displayed);
+      return Qt;
+    }
 
   /* Make this buffer not be current.  Exit if it is the sole visible
      buffer.  */
@@ -1747,15 +1775,13 @@ cleaning up all windows currently displaying the buffer to be killed. */)
 
   kill_buffer_processes (buffer);
 
-  /* Killing a buffer might have global effects which require
-     redisplaying frames.  For example, if the buffer's name appears
-     in the frame title.  */
-  windows_or_buffers_changed = 11;
-
   /* Killing buffer processes may run sentinels which may have killed
      our buffer.  */
   if (!BUFFER_LIVE_P (b))
-    return Qt;
+    {
+      set_update_modelines_for_buf (buffer_was_displayed);
+      return Qt;
+    }
 
   /* These may run Lisp code and into infinite loops (if someone
      insisted on circular lists) so allow quitting here.  */
@@ -1787,7 +1813,10 @@ cleaning up all windows currently displaying the buffer to be killed. */)
 
   /* Deleting an auto-save file could have killed our buffer.  */
   if (!BUFFER_LIVE_P (b))
-    return Qt;
+    {
+      set_update_modelines_for_buf (buffer_was_displayed);
+      return Qt;
+    }
 
   if (b->base_buffer)
     {
@@ -1886,6 +1915,7 @@ cleaning up all windows currently displaying the buffer to be killed. */)
   if (!NILP (Vrun_hooks))
     call1 (Vrun_hooks, Qbuffer_list_update_hook);
 
+  set_update_modelines_for_buf (buffer_was_displayed);
   return Qt;
 }