Fix problems with line-number updates in Follow mode

* src/xdisp.c (redisplay_window): If forced window-start requires
to move a window's point, and the window is under relative
line-number display, force another round of redisplay to update
the relative line numbers.  This fixes follow-mode "redisplay" of
its window group.

* lisp/frame.el: Add display-line-numbers to the list of variables
that should trigger redisplay of the current buffer.

2 files changed, 9 insertions, 4 deletions

diff --git a/lisp/frame.el b/lisp/frame.el
index b7a55169281..8f51afa2a9a 100644
--- a/lisp/frame.el
+++ b/lisp/frame.el
@@ -2434,6 +2434,7 @@ See also `toggle-frame-maximized'."
         line-prefix
         wrap-prefix
         truncate-lines
+        display-line-numbers
         bidi-paragraph-direction
         bidi-display-reordering))
 
diff --git a/src/xdisp.c b/src/xdisp.c
index 39176e0e675..9b5762550d7 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -16800,10 +16800,14 @@ redisplay_window (Lisp_Object window, bool just_this_one_p)
           XBUFFER (w->contents)->text->redisplay = false;
           safe__call1 (true, Vpre_redisplay_function, Fcons (window, Qnil));
 
-          if (w->redisplay || XBUFFER (w->contents)->text->redisplay)
-            {
-              /* pre-redisplay-function made changes (e.g. move the region)
-                 that require another round of redisplay.  */
+          if (w->redisplay || XBUFFER (w->contents)->text->redisplay
+              || (EQ (Vdisplay_line_numbers, Qrelative)
+                  && row != MATRIX_FIRST_TEXT_ROW (w->desired_matrix)))
+            {
+              /* Either pre-redisplay-function made changes (e.g. move
+                 the region), or we moved point in a window that is
+                 under display-line-numbers = relative mode.  We need
+                 another round of redisplay.  */
               clear_glyph_matrix (w->desired_matrix);
               if (!try_window (window, startp, 0))
                 goto need_larger_matrices;