Fix copying properties in 'format' when it produces padding

* src/textprop.c (extend_property_ranges): Correct range extension
when the new end is beyond the old end.  (Bug#23859)

1 files changed, 8 insertions, 3 deletions

diff --git a/src/textprop.c b/src/textprop.c
index c4e49d98ebc..aabd5671e76 100644
--- a/src/textprop.c
+++ b/src/textprop.c
@@ -2065,9 +2065,14 @@ extend_property_ranges (Lisp_Object list, Lisp_Object new_end)
           else
             XSETCDR (prev, XCDR (list));
         }
-      else if (XINT (end) > max)
-        /* The end-point is past the end of the new string.  */
-        XSETCAR (XCDR (item), new_end);
+      else if (XINT (end) != max)
+        {
+          /* Either the end-point is past the end of the new string,
+             and we need to discard the properties past the new end,
+             or the caller is extending the property range, and we
+             should update the end-point to reflect that.  */
+          XSETCAR (XCDR (item), new_end);
+        }
     }
 
   return head;