Avoid infloop when scrolling under scroll-preserve-screen-position

* src/window.c (window_scroll_pixel_based): If screen position is
to be preserved, make sure its recorded Y coordinate is outside
the scroll margin.  (Bug#28342)

1 files changed, 5 insertions, 0 deletions

diff --git a/src/window.c b/src/window.c
index 857870591f3..18adb62538b 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5335,6 +5335,11 @@ window_scroll_pixel_based (Lisp_Object window, int n, bool whole, bool noerror)
                 break;
             }
           SET_PT_BOTH (IT_CHARPOS (it), IT_BYTEPOS (it));
+          /* Fix up the Y position to preserve, if it is inside the
+             scroll margin at the window top.  */
+          if (window_scroll_pixel_based_preserve_y >= 0
+              && window_scroll_pixel_based_preserve_y < this_scroll_margin)
+            window_scroll_pixel_based_preserve_y = this_scroll_margin;
         }
     }
   else if (n < 0)