Do not create empty overlays with the evaporate property (Bug#9642).

* buffer.c (Fmove_overlay): Delete an evaporating overlay
if it becomes empty after its bounds are adjusted to fit within
its buffer.  Without this fix, in a nonempty buffer (let ((o
(make-overlay 1 2))) (overlay-put o 'evaporate t) (move-overlay o 0 1))
yields an empty overlay that has the evaporate property, which is
not supposed to happen.

1 files changed, 19 insertions, 18 deletions

diff --git a/src/buffer.c b/src/buffer.c
index 9bac3ec742b..6c2e21c8125 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -3682,6 +3682,7 @@ buffer.  */)
   struct buffer *b, *ob;
   Lisp_Object obuffer;
   int count = SPECPDL_INDEX ();
+  ptrdiff_t n_beg, n_end;
 
   CHECK_OVERLAY (overlay);
   if (NILP (buffer))
@@ -3700,15 +3701,23 @@ buffer.  */)
   CHECK_NUMBER_COERCE_MARKER (beg);
   CHECK_NUMBER_COERCE_MARKER (end);
 
-  if (XINT (beg) == XINT (end) && ! NILP (Foverlay_get (overlay, Qevaporate)))
-    return Fdelete_overlay (overlay);
-
   if (XINT (beg) > XINT (end))
     {
       Lisp_Object temp;
       temp = beg; beg = end; end = temp;
     }
 
+  /* First set the overlay boundaries, which may clip them.  */
+  Fset_marker (OVERLAY_START (overlay), beg, buffer);
+  Fset_marker (OVERLAY_END (overlay), end, buffer);
+  n_beg = marker_position (OVERLAY_START (overlay));
+  n_end = marker_position (OVERLAY_END (overlay));
+
+  /* Now, delete the overlay if it is empty after clipping and has the
+     evaporate property.  */
+  if (n_beg == n_end && ! NILP (Foverlay_get (overlay, Qevaporate)))
+    return Fdelete_overlay (overlay);
+
   specbind (Qinhibit_quit, Qt);
 
   obuffer = Fmarker_buffer (OVERLAY_START (overlay));
@@ -3731,7 +3740,7 @@ buffer.  */)
         }
 
       /* Redisplay where the overlay is going to be.  */
-      modify_overlay (b, XINT (beg), XINT (end));
+      modify_overlay (b, n_beg, n_end);
     }
   else
     /* Redisplay the area the overlay has just left, or just enclosed.  */
@@ -3741,16 +3750,12 @@ buffer.  */)
       o_beg = OVERLAY_POSITION (OVERLAY_START (overlay));
       o_end = OVERLAY_POSITION (OVERLAY_END (overlay));
 
-      if (o_beg == XINT (beg))
-        modify_overlay (b, o_end, XINT (end));
-      else if (o_end == XINT (end))
-        modify_overlay (b, o_beg, XINT (beg));
+      if (o_beg == n_beg)
+        modify_overlay (b, o_end, n_end);
+      else if (o_end == n_end)
+        modify_overlay (b, o_beg, n_beg);
       else
-        {
-          if (XINT (beg) < o_beg) o_beg = XINT (beg);
-          if (XINT (end) > o_end) o_end = XINT (end);
-          modify_overlay (b, o_beg, o_end);
-        }
+        modify_overlay (b, min (o_beg, n_beg), max (o_end, n_end));
     }
 
   if (!NILP (obuffer))
@@ -3762,12 +3767,8 @@ buffer.  */)
       eassert (XOVERLAY (overlay)->next == NULL);
     }
 
-  Fset_marker (OVERLAY_START (overlay), beg, buffer);
-  Fset_marker (OVERLAY_END   (overlay), end, buffer);
-
   /* Put the overlay on the wrong list.  */
-  end = OVERLAY_END (overlay);
-  if (OVERLAY_POSITION (end) < b->overlay_center)
+  if (n_end < b->overlay_center)
     {
       XOVERLAY (overlay)->next = b->overlays_after;
       b->overlays_after = XOVERLAY (overlay);