vim-patch:9.0.0734: cursor position invalid when scrolling with 'smoothscroll'

Problem:    Cursor position invalid when scrolling with 'smoothscroll' set.
            (Ernie Rael)
Solution:   Add w_valid_skipcol and clear flags when it changes.  Adjust
            w_skipcol after moving the cursor.

https://github.com/vim/vim/commit/2fbabd238a94022c99506e920186a5b6cdf15426

Co-authored-by: Bram Moolenaar <Bram@vim.org>

6 files changed, 130 insertions, 10 deletions

diff --git a/src/nvim/buffer_defs.h b/src/nvim/buffer_defs.h
index 456acfd798..0f832d3659 100644
--- a/src/nvim/buffer_defs.h
+++ b/src/nvim/buffer_defs.h
@@ -1223,6 +1223,7 @@ struct window_S {
   int w_valid;
   pos_T w_valid_cursor;             // last known position of w_cursor, used to adjust w_valid
   colnr_T w_valid_leftcol;          // last known w_leftcol
+  colnr_T w_valid_skipcol;          // last known w_skipcol
 
   bool w_viewport_invalid;
   linenr_T w_viewport_last_topline;  // topline when the viewport was last updated
diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 0fb1102f4f..18434ad69f 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -2449,6 +2449,7 @@ void beginline(int flags)
     }
     curwin->w_set_curswant = true;
   }
+  adjust_skipcol();
 }
 
 // oneright oneleft cursor_down cursor_up
@@ -2490,6 +2491,7 @@ int oneright(void)
   curwin->w_cursor.col += l;
 
   curwin->w_set_curswant = true;
+  adjust_skipcol();
   return OK;
 }
 
@@ -2538,6 +2540,7 @@ int oneleft(void)
   // if the character on the left of the current cursor is a multi-byte
   // character, move to its first byte
   mb_adjust_cursor();
+  adjust_skipcol();
   return OK;
 }
 
diff --git a/src/nvim/move.c b/src/nvim/move.c
index e7f5959dbb..b2cf1ebc03 100644
--- a/src/nvim/move.c
+++ b/src/nvim/move.c
@@ -426,7 +426,15 @@ void check_cursor_moved(win_T *wp)
                      |VALID_CHEIGHT|VALID_CROW|VALID_TOPLINE);
     wp->w_valid_cursor = wp->w_cursor;
     wp->w_valid_leftcol = wp->w_leftcol;
+    wp->w_valid_skipcol = wp->w_skipcol;
     wp->w_viewport_invalid = true;
+  } else if (wp->w_skipcol != wp->w_valid_skipcol) {
+    wp->w_valid &= ~(VALID_WROW|VALID_WCOL|VALID_VIRTCOL
+                     |VALID_CHEIGHT|VALID_CROW
+                     |VALID_BOTLINE|VALID_BOTLINE_AP);
+    wp->w_valid_cursor = wp->w_cursor;
+    wp->w_valid_leftcol = wp->w_leftcol;
+    wp->w_valid_skipcol = wp->w_skipcol;
   } else if (wp->w_cursor.col != wp->w_valid_cursor.col
              || wp->w_leftcol != wp->w_valid_leftcol
              || wp->w_cursor.coladd !=
@@ -786,6 +794,12 @@ void curs_columns(win_T *wp, int may_scroll)
   } else if (wp->w_p_wrap && wp->w_width_inner != 0) {
     width = textwidth + win_col_off2(wp);
 
+    // skip columns that are not visible
+    if (wp->w_cursor.lnum == wp->w_topline
+        && wp->w_wcol >= wp->w_skipcol) {
+      wp->w_wcol -= wp->w_skipcol;
+    }
+
     // long line wrapping, adjust wp->w_wrow
     if (wp->w_wcol >= wp->w_width_inner) {
       // this same formula is used in validate_cursor_col()
@@ -929,11 +943,11 @@ void curs_columns(win_T *wp, int may_scroll)
         endcol -= width;
       }
       if (endcol > wp->w_skipcol) {
+        wp->w_wrow -= (endcol - wp->w_skipcol) / width;
         wp->w_skipcol = endcol;
       }
     }
 
-    wp->w_wrow -= wp->w_skipcol / width;
     if (wp->w_wrow >= wp->w_height_inner) {
       // small window, make sure cursor is in it
       extra = wp->w_wrow - wp->w_height_inner + 1;
@@ -953,8 +967,10 @@ void curs_columns(win_T *wp, int may_scroll)
 
   redraw_for_cursorcolumn(curwin);
 
-  // now w_leftcol is valid, avoid check_cursor_moved() thinking otherwise
+  // now w_leftcol and w_skipcol are valid, avoid check_cursor_moved()
+  // thinking otherwise
   wp->w_valid_leftcol = wp->w_leftcol;
+  wp->w_valid_skipcol = wp->w_skipcol;
 
   wp->w_valid |= VALID_WCOL|VALID_WROW|VALID_VIRTCOL;
 }
@@ -1352,15 +1368,70 @@ bool scrollup(long line_count, int byfold)
       }
       curwin->w_curswant = col;
       coladvance(curwin->w_curswant);
+
+      // validate_virtcol() marked various things as valid, but after
+      // moving the cursor they need to be recomputed
+      curwin->w_valid &= ~(VALID_WROW|VALID_WCOL|VALID_CHEIGHT|VALID_CROW|VALID_VIRTCOL);
     }
   }
 
-  bool moved = topline != curwin->w_topline
-               || botline != curwin->w_botline;
+  bool moved = topline != curwin->w_topline || botline != curwin->w_botline;
 
   return moved;
 }
 
+/// Called after changing the cursor column: make sure that curwin->w_skipcol is
+/// valid for 'smoothscroll'.
+void adjust_skipcol(void)
+{
+  if (!curwin->w_p_wrap || !curwin->w_p_sms || curwin->w_cursor.lnum != curwin->w_topline) {
+    return;
+  }
+
+  int width1 = curwin->w_width - curwin_col_off();
+  int width2 = width1 + curwin_col_off2();
+  long so = curwin->w_p_so >= 0 ? curwin->w_p_so : p_so;
+  long scrolloff_cols = so == 0 ? 0 : width1 + (so - 1) * width2;
+  bool scrolled = false;
+
+  validate_virtcol();
+  while (curwin->w_skipcol > 0
+         && curwin->w_virtcol < curwin->w_skipcol + 3 + scrolloff_cols) {
+    // scroll a screen line down
+    if (curwin->w_skipcol >= width1 + width2) {
+      curwin->w_skipcol -= width2;
+    } else {
+      curwin->w_skipcol -= width1;
+    }
+    redraw_later(curwin, UPD_NOT_VALID);
+    scrolled = true;
+    validate_virtcol();
+  }
+  if (scrolled) {
+    return;  // don't scroll in the other direction now
+  }
+  long col = curwin->w_virtcol - curwin->w_skipcol + scrolloff_cols;
+  int row = 0;
+  if (col >= width1) {
+    col -= width1;
+    row++;
+  }
+  if (col > width2) {
+    row += (int)col / width2;
+    col = col % width2;
+  }
+  if (row >= curwin->w_height) {
+    if (curwin->w_skipcol == 0) {
+      curwin->w_skipcol += width1;
+      row--;
+    }
+    if (row >= curwin->w_height) {
+      curwin->w_skipcol += (row - curwin->w_height) * width2;
+    }
+    redraw_later(curwin, UPD_NOT_VALID);
+  }
+}
+
 /// Don't end up with too many filler lines in the window.
 ///
 /// @param down  when true scroll down when not enough space
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index a51bde967e..d4759aeaba 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -2566,6 +2566,8 @@ static bool nv_screengo(oparg_T *oap, int dir, long dist)
   if (atend) {
     curwin->w_curswant = MAXCOL;            // stick in the last column
   }
+  adjust_skipcol();
+
   return retval;
 }
 
diff --git a/test/functional/legacy/scroll_opt_spec.lua b/test/functional/legacy/scroll_opt_spec.lua
index be7d324908..a5660ae4d2 100644
--- a/test/functional/legacy/scroll_opt_spec.lua
+++ b/test/functional/legacy/scroll_opt_spec.lua
@@ -428,14 +428,36 @@ describe('smoothscroll', function()
                                               |
     ]])
     -- 'scrolloff' set to 2, scrolling down, cursor moves screen line up
-    feed('<C-E>gjgj<C-Y>')
+    feed('<C-E>gj<C-Y>')
+    screen:expect_unchanged()
+  end)
+
+  -- oldtest: Test_smoothscroll_one_long_line()
+  it("scrolls correctly when moving the cursor", function()
+    screen:try_resize(40, 6)
+    exec([[
+      call setline(1, 'with lots of text '->repeat(7))
+      set smoothscroll scrolloff=0
+    ]])
+    local s1 = [[
+      ^with lots of text with lots of text with|
+       lots of text with lots of text with lot|
+      s of text with lots of text with lots of|
+       text                                   |
+      ~                                       |
+                                              |
+    ]]
+    screen:expect(s1)
+    feed('<C-E>')
     screen:expect([[
-      <<<of text with lots of text with lots o|
-      f text with lots of text with lots of te|
-      xt with l^ots of text with lots of text w|
-      ith lots of text with lots of text with |
-      lots of text with lots of text with lots|
+      <<<ts of text with lots of text with lot|
+      ^s of text with lots of text with lots of|
+       text                                   |
+      ~                                       |
+      ~                                       |
                                               |
     ]])
+    feed('0')
+    screen:expect(s1)
   end)
 end)
diff --git a/test/old/testdir/test_scroll_opt.vim b/test/old/testdir/test_scroll_opt.vim
index 3317ec9209..a8e0a1109a 100644
--- a/test/old/testdir/test_scroll_opt.vim
+++ b/test/old/testdir/test_scroll_opt.vim
@@ -265,5 +265,26 @@ func Test_smoothscroll_wrap_long_line()
   call StopVimInTerminal(buf)
 endfunc
 
+func Test_smoothscroll_one_long_line()
+  CheckScreendump
+
+  let lines =<< trim END
+      vim9script
+      setline(1, 'with lots of text '->repeat(7))
+      set smoothscroll scrolloff=0
+  END
+  call writefile(lines, 'XSmoothOneLong', 'D')
+  let buf = RunVimInTerminal('-S XSmoothOneLong', #{rows: 6, cols: 40})
+  call VerifyScreenDump(buf, 'Test_smooth_one_long_1', {})
+  
+  call term_sendkeys(buf, "\<C-E>")
+  call VerifyScreenDump(buf, 'Test_smooth_one_long_2', {})
+
+  call term_sendkeys(buf, "0")
+  call VerifyScreenDump(buf, 'Test_smooth_one_long_1', {})
+
+  call StopVimInTerminal(buf)
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab