Fix cursor position under scroll-conservatively and overlay strings

* src/xdisp.c (try_scrolling): Handle the case where the last
visible screen line of a window displays a before- or after-string
that takes up the whole screen line, and therefore there's no
place to display the cursor, even though the window does seem to
include the position of point.  (Bug#24179)

1 files changed, 34 insertions, 0 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index efd5f54fa39..21fc01f1e69 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -15313,6 +15313,40 @@ try_scrolling (Lisp_Object window, bool just_this_one_p,
           if (dy > 0)
             scroll_down_p = true;
         }
+      else if (PT == IT_CHARPOS (it)
+               && IT_CHARPOS (it) < ZV
+               && it.method == GET_FROM_STRING
+               && arg_scroll_conservatively > scroll_limit
+               && it.current_x == 0)
+        {
+          enum move_it_result skip;
+          int y1 = it.current_y;
+          int vpos;
+
+          /* A before-string that includes newlines and is displayed
+             on the last visible screen line could fail us under
+             scroll-conservatively > 100, because we will be unable to
+             position the cursor on that last visible line.  Try to
+             recover by finding the first screen line that has some
+             glyphs coming from the buffer text.  */
+          do {
+            skip = move_it_in_display_line_to (&it, ZV, -1, MOVE_TO_POS);
+            if (skip != MOVE_NEWLINE_OR_CR
+                || IT_CHARPOS (it) != PT
+                || it.method == GET_FROM_BUFFER)
+              break;
+            vpos = it.vpos;
+            move_it_to (&it, -1, -1, -1, vpos + 1, MOVE_TO_VPOS);
+          } while (it.vpos > vpos);
+
+          dy = it.current_y - y1;
+
+          if (dy > scroll_max)
+            return SCROLLING_FAILED;
+
+          if (dy > 0)
+            scroll_down_p = true;
+        }
     }
 
   if (scroll_down_p)