bug#56683: 29.0.50; long lines fix doesn't work correctly when lines are truncated

[Gerd Möllmann]

Eli Zaretskii <eliz@gnu.org> writes:

> I think we should take look at this fragment from hscroll_window_tree:
>
>             /* Move iterator to pt starting at cursor_row->start in
>                a line with infinite width.  */
>             init_to_row_start (&it, w, cursor_row);
>             if (hscl)
>               it.first_visible_x = window_hscroll_limited (w, it.f)
>                                    * FRAME_COLUMN_WIDTH (it.f);
>             it.last_visible_x = DISP_INFINITY;
>             move_it_in_display_line_to (&it, pt, -1, MOVE_TO_POS);
>             /* If the line ends in an overlay string with a newline,
>                we might infloop, because displaying the window will
>                want to put the cursor after the overlay, i.e. at X
>                coordinate of zero on the next screen line.  So we
>                use the buffer position prior to the overlay string
>                instead.  */
>             if (it.method == GET_FROM_STRING && pt > 1)
>               {
>                 init_to_row_start (&it, w, cursor_row);
>                 if (hscl)
>                   it.first_visible_x = (window_hscroll_limited (w, it.f)
>                                         * FRAME_COLUMN_WIDTH (it.f));
>                 move_it_in_display_line_to (&it, pt - 1, -1, MOVE_TO_POS);
>               }
>
> Specifically, init_to_row_start can potentially start from a very far
> away buffer position, especially in buffers with a single long line,

I'm not sure. Cursor_row comes from here:

          if (w->cursor.vpos < bottom_row - w->desired_matrix->rows)
            cursor_row = MATRIX_ROW (w->desired_matrix, w->cursor.vpos);
          else
            cursor_row = bottom_row - 1;

          if (!cursor_row->enabled_p)
            {
              bottom_row = MATRIX_BOTTOM_TEXT_ROW (w->current_matrix, w);
              if (w->cursor.vpos < bottom_row - w->current_matrix->rows)
                cursor_row = MATRIX_ROW (w->current_matrix, w->cursor.vpos);
              else
                cursor_row = bottom_row - 1;
            }

In my own words, either cursor_row has just been produced in the
desired_matrix, or it has been produced previously, and is now part of
the current matrix.

Doesn't that mean it was already subject to the iterator narrowing?