From bd28cae1f1c21c0e3743e3427c98bbd848fad237 Mon Sep 17 00:00:00 2001
From: Luuk van Baal <luukvbaal@gmail.com>
Date: Wed, 3 Apr 2024 22:50:40 +0200
Subject: patch 9.1.0260: Problems with "zb" and scrolling to new topline with
 'smoothscroll'

Problem: "zb" does not reveal filler lines at the start of a buffer.
          Scrolled cursor position with 'smoothscroll' is unpredictable,
          and may reset skipcol later if it is not visible (after v9.1.258)
Solution: Replace confusing for loop that reaches final control value too
          early with while loop. Set "w_curswant" accordingly so cursor
          will be placed in visible part of topline.
          (Luuk van Baal)

closes: #14394

Signed-off-by: Luuk van Baal <luukvbaal@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
---
 src/testdir/test_normal.vim     | 15 +++++++++++++++
 src/testdir/test_scroll_opt.vim |  9 ++++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)

(limited to 'src/testdir')

diff --git a/src/testdir/test_normal.vim b/src/testdir/test_normal.vim
index 1acdfcecbb..5b1bb402b6 100644
--- a/src/testdir/test_normal.vim
+++ b/src/testdir/test_normal.vim
@@ -4210,4 +4210,19 @@ func Test_single_line_scroll()
   call prop_type_delete(vt)
 endfunc
 
+" Test for zb in buffer with a single line and filler lines
+func Test_single_line_filler_zb()
+  call setline(1, ['', 'foobar one two three'])
+  diffthis
+  new
+  call setline(1, ['foobar one two three'])
+  diffthis
+
+  " zb scrolls to reveal filler lines at the start of the buffer.
+  exe "normal \<C-E>zb"
+  call assert_equal(1, winsaveview().topfill)
+
+  bw!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab nofoldenable
diff --git a/src/testdir/test_scroll_opt.vim b/src/testdir/test_scroll_opt.vim
index dd2af0125b..294da0d877 100644
--- a/src/testdir/test_scroll_opt.vim
+++ b/src/testdir/test_scroll_opt.vim
@@ -1018,6 +1018,8 @@ func Test_smoothscroll_page()
   call assert_equal(0, winsaveview().skipcol)
 
   " Half-page scrolling does not go beyond end of buffer and moves the cursor.
+  " Even with 'nostartofline', the correct amount of lines is scrolled.
+  setl nostartofline
   exe "norm! 0\<C-D>"
   call assert_equal(200, winsaveview().skipcol)
   call assert_equal(204, col('.'))
@@ -1041,7 +1043,7 @@ func Test_smoothscroll_page()
   call assert_equal(204, col('.'))
   exe "norm! \<C-U>"
   call assert_equal(0, winsaveview().skipcol)
-  call assert_equal(1, col('.'))
+  call assert_equal(40, col('.'))
 
   bwipe!
 endfunc
@@ -1059,6 +1061,11 @@ func Test_smoothscroll_next_topline()
   redraw
   call assert_equal(0, winsaveview().skipcol)
 
+  " Also when scrolling back.
+  exe "norm! G\<C-Y>"
+  redraw
+  call assert_equal(880, winsaveview().skipcol)
+
   " Cursor in correct place when not in the first screenline of a buffer line.
   exe "norm! gg4gj20\<C-D>\<C-D>"
   redraw
-- 
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