vim-patch:9.1.0753: Wrong display when typing in diff mode with 'smoothscroll' (#30614)

Problem:  Wrong display when typing in diff mode with 'smoothscroll'.
Solution: Use adjust_plines_for_skipcol() (zeertzjq).

closes: vim/vim#15776

https://github.com/vim/vim/commit/47f8584a80006cd25e7dc6fa7fb1bfe2e768403c

1 files changed, 30 insertions, 0 deletions

diff --git a/test/old/testdir/test_scroll_opt.vim b/test/old/testdir/test_scroll_opt.vim
index 5bf071903b..55f9a32718 100644
--- a/test/old/testdir/test_scroll_opt.vim
+++ b/test/old/testdir/test_scroll_opt.vim
@@ -302,6 +302,36 @@ func Test_smoothscroll_diff_mode()
   call StopVimInTerminal(buf)
 endfunc
 
+func Test_smoothscroll_diff_change_line()
+  CheckScreendump
+
+  let lines =<< trim END
+    set diffopt+=followwrap smoothscroll
+    call setline(1, repeat(' abc', &columns))
+    call setline(2, 'bar')
+    call setline(3, repeat(' abc', &columns))
+    vnew
+    call setline(1, repeat(' abc', &columns))
+    call setline(2, 'foo')
+    call setline(3, 'bar')
+    call setline(4, repeat(' abc', &columns))
+    windo exe "normal! 2gg5\<C-E>"
+    windo diffthis
+  END
+  call writefile(lines, 'XSmoothDiffChangeLine', 'D')
+  let buf = RunVimInTerminal('-S XSmoothDiffChangeLine', #{rows: 20, columns: 55})
+
+  call VerifyScreenDump(buf, 'Test_smooth_diff_change_line_1', {})
+  call term_sendkeys(buf, "Abar")
+  call VerifyScreenDump(buf, 'Test_smooth_diff_change_line_2', {})
+  call term_sendkeys(buf, "\<Esc>")
+  call VerifyScreenDump(buf, 'Test_smooth_diff_change_line_3', {})
+  call term_sendkeys(buf, "yyp")
+  call VerifyScreenDump(buf, 'Test_smooth_diff_change_line_4', {})
+
+  call StopVimInTerminal(buf)
+endfunc
+
 func Test_smoothscroll_wrap_scrolloff_zero()
   CheckScreendump