vim-patch:9.0.1530: cursor moves to wrong line when 'foldmethod' is "diff"

Problem:    Cursor moves to wrong line when 'foldmethod' is "diff". (Rick
            Howe)
Solution:   Adjust logic for scrolling. (Luuk van Baal, closes vim/vim#12364,
            closes vim/vim#12218)

https://github.com/vim/vim/commit/aa6ba308a1498dc8da04d1d30ec0470018bf782a

3 files changed, 69 insertions, 37 deletions

diff --git a/src/nvim/move.c b/src/nvim/move.c
index cff3e264f8..9e053b2db5 100644
--- a/src/nvim/move.c
+++ b/src/nvim/move.c
@@ -1318,14 +1318,6 @@ bool scrolldown(long line_count, int byfold)
   return moved;
 }
 
-/// Return TRUE if scrollup() will scroll by screen line rather than text line.
-static int scrolling_screenlines(bool byfold)
-{
-  return (curwin->w_p_wrap && curwin->w_p_sms)
-         || (byfold && hasAnyFolding(curwin))
-         || (curwin->w_p_diff && !curwin->w_p_wrap);
-}
-
 /// Scroll the current window up by "line_count" logical lines.  "CTRL-E"
 ///
 /// @param line_count number of lines to scroll
@@ -1336,7 +1328,7 @@ bool scrollup(long line_count, int byfold)
   linenr_T botline = curwin->w_botline;
   int do_sms = curwin->w_p_wrap && curwin->w_p_sms;
 
-  if (scrolling_screenlines(byfold) || win_may_fill(curwin)) {
+  if (do_sms || (byfold && hasAnyFolding(curwin)) || win_may_fill(curwin)) {
     int width1 = curwin->w_width_inner - curwin_col_off();
     int width2 = width1 + curwin_col_off2();
     unsigned size = 0;
@@ -1873,6 +1865,7 @@ void scroll_cursor_bot(int min_scroll, int set_topbot)
   int old_valid = curwin->w_valid;
   int old_empty_rows = curwin->w_empty_rows;
   linenr_T cln = curwin->w_cursor.lnum;  // Cursor Line Number
+  int do_sms = curwin->w_p_wrap && curwin->w_p_sms;
 
   if (set_topbot) {
     bool set_skipcol = false;
@@ -1889,7 +1882,7 @@ void scroll_cursor_bot(int min_scroll, int set_topbot)
         break;
       }
       if (used + loff.height > curwin->w_height_inner) {
-        if (curwin->w_p_sms && curwin->w_p_wrap) {
+        if (do_sms) {
           // 'smoothscroll' and 'wrap' are set.  The above line is
           // too long to show in its entirety, so we show just a part
           // of it.
@@ -1928,7 +1921,6 @@ void scroll_cursor_bot(int min_scroll, int set_topbot)
   used = plines_win_nofill(curwin, cln, true);
 
   int scrolled = 0;
-  int min_scrolled = 1;
   // If the cursor is on or below botline, we will at least scroll by the
   // height of the cursor line, which is "used".  Correct for empty lines,
   // which are really part of botline.
@@ -1937,16 +1929,8 @@ void scroll_cursor_bot(int min_scroll, int set_topbot)
     if (cln == curwin->w_botline) {
       scrolled -= curwin->w_empty_rows;
     }
-    min_scrolled = scrolled;
-    if (curwin->w_p_sms && curwin->w_p_wrap) {
-      // 'smoothscroll' and 'wrap' are set
-      if (cln > curwin->w_botline) {
-        // add screen lines below w_botline
-        for (linenr_T lnum = curwin->w_botline + 1; lnum <= cln; lnum++) {
-          min_scrolled += plines_win_nofill(curwin, lnum, true);
-        }
-      }
-
+    if (do_sms) {
+      // 'smoothscroll' and 'wrap' are set.
       // Calculate how many screen lines the current top line of window
       // occupies. If it is occupying more than the entire window, we
       // need to scroll the additional clipped lines to scroll past the
@@ -1965,7 +1949,6 @@ void scroll_cursor_bot(int min_scroll, int set_topbot)
       top_plines -= skip_lines;
       if (top_plines > curwin->w_height_inner) {
         scrolled += (top_plines - curwin->w_height_inner);
-        min_scrolled += (top_plines - curwin->w_height_inner);
       }
     }
   }
@@ -2070,21 +2053,11 @@ void scroll_cursor_bot(int min_scroll, int set_topbot)
   // Otherwise put it at 1/2 of the screen.
   if (line_count >= curwin->w_height_inner && line_count > min_scroll) {
     scroll_cursor_halfway(false, true);
-  } else {
-    // With 'smoothscroll' scroll at least the height of the cursor line,
-    // unless it would move the cursor.
-    if (curwin->w_p_wrap && curwin->w_p_sms && line_count < min_scrolled
-        && (curwin->w_cursor.lnum < curwin->w_topline
-            || (curwin->w_virtcol - curwin->w_skipcol >=
-                curwin->w_width_inner - curwin_col_off()))) {
-      line_count = min_scrolled;
-    }
-    if (line_count > 0) {
-      if (scrolling_screenlines(true)) {
-        scrollup(scrolled, true);  // TODO(vim):
-      } else {
-        scrollup(line_count, true);
-      }
+  } else if (line_count > 0) {
+    if (do_sms) {
+      scrollup(scrolled, true);  // TODO(vim):
+    } else {
+      scrollup(line_count, true);
     }
   }
 
diff --git a/test/functional/legacy/normal_spec.lua b/test/functional/legacy/normal_spec.lua
new file mode 100644
index 0000000000..ba875460f5
--- /dev/null
+++ b/test/functional/legacy/normal_spec.lua
@@ -0,0 +1,41 @@
+local helpers = require('test.functional.helpers')(after_each)
+local Screen = require('test.functional.ui.screen')
+local clear = helpers.clear
+local exec = helpers.exec
+
+before_each(clear)
+
+describe('normal', function()
+  -- oldtest: Test_normal_j_below_botline()
+  it([["j" does not skip lines when scrolling below botline and 'foldmethod' is not "manual"]], function()
+    local screen = Screen.new(40, 19)
+    screen:attach()
+    screen:set_default_attr_ids({{foreground = Screen.colors.Brown}})
+    exec([[
+      set number foldmethod=diff scrolloff=0
+      call setline(1, map(range(1, 9), 'repeat(v:val, 200)'))
+      norm Lj
+    ]])
+    screen:expect([[
+      {1:  2 }222222222222222222222222222222222222|
+      {1:    }222222222222222222222222222222222222|
+      {1:    }222222222222222222222222222222222222|
+      {1:    }222222222222222222222222222222222222|
+      {1:    }222222222222222222222222222222222222|
+      {1:    }22222222222222222222                |
+      {1:  3 }333333333333333333333333333333333333|
+      {1:    }333333333333333333333333333333333333|
+      {1:    }333333333333333333333333333333333333|
+      {1:    }333333333333333333333333333333333333|
+      {1:    }333333333333333333333333333333333333|
+      {1:    }33333333333333333333                |
+      {1:  4 }^444444444444444444444444444444444444|
+      {1:    }444444444444444444444444444444444444|
+      {1:    }444444444444444444444444444444444444|
+      {1:    }444444444444444444444444444444444444|
+      {1:    }444444444444444444444444444444444444|
+      {1:    }44444444444444444444                |
+                                              |
+    ]])
+  end)
+end)
diff --git a/test/old/testdir/test_normal.vim b/test/old/testdir/test_normal.vim
index a854c9538f..23baebb78c 100644
--- a/test/old/testdir/test_normal.vim
+++ b/test/old/testdir/test_normal.vim
@@ -3993,4 +3993,22 @@ func Test_mouse_shape_after_cancelling_gr()
   call delete('Xmouseshapes')
 endfunc
 
+" Test that "j" does not skip lines when scrolling below botline and
+" 'foldmethod' is not "manual".
+func Test_normal_j_below_botline()
+  CheckScreendump
+
+  let lines =<< trim END
+    set number foldmethod=diff scrolloff=0
+    call setline(1, map(range(1, 9), 'repeat(v:val, 200)'))
+    norm Lj
+  END
+  call writefile(lines, 'XNormalJBelowBotline', 'D')
+  let buf = RunVimInTerminal('-S XNormalJBelowBotline', #{rows: 19, cols: 40})
+
+  call VerifyScreenDump(buf, 'Test_normal_j_below_botline', {})
+
+  call StopVimInTerminal(buf)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab