fix(drawline): check filler_todo in place of removed draw_state (#27889)

The only place it matters is the conceal wcol check, but it can avoid
unnecessary computations at other places.

src/nvim/drawline.c

@@ -1596,7 +1596,8 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
       }
     }
 
-    if (cul_screenline && wlv.vcol >= left_curline_col && wlv.vcol < right_curline_col) {
+    if (cul_screenline && wlv.filler_todo <= 0
+        && wlv.vcol >= left_curline_col && wlv.vcol < right_curline_col) {
       apply_cursorline_highlight(wp, &wlv);
     }
 
@@ -1623,7 +1624,8 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
     }
 
     int extmark_attr = 0;
-    if (area_highlighting || spv->spv_has_spell || extra_check) {
+    if (wlv.filler_todo <= 0
+        && (area_highlighting || spv->spv_has_spell || extra_check)) {
       if (wlv.n_extra == 0 || !wlv.extra_for_extmark) {
         wlv.reset_extra_attr = false;
       }
@@ -1654,11 +1656,9 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
           }
           decor_need_recheck = false;
         }
-        if (wlv.filler_todo <= 0) {
         extmark_attr = decor_redraw_col(wp, (colnr_T)(ptr - line),
                                         may_have_inline_virt ? -3 : wlv.off,
                                         selected, &decor_state);
-        }
         if (may_have_inline_virt) {
           handle_inline_virtual_text(wp, &wlv, ptr - line, selected);
           if (wlv.n_extra > 0 && wlv.virt_inline_hl_mode <= kHlModeReplace) {
@@ -2443,7 +2443,7 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
     // the cursor column when we reach its position.
     // With 'virtualedit' we may never reach cursor position, but we still
     // need to correct the cursor column, so do that at end of line.
-    if (!did_wcol
+    if (!did_wcol && wlv.filler_todo <= 0
         && wp == curwin && lnum == wp->w_cursor.lnum
         && conceal_cursor_line(wp)
         && (wlv.vcol + wlv.skip_cells >= wp->w_virtcol || mb_schar == NUL)) {
@@ -2705,10 +2705,14 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
       }
     }
 
+    if (wlv.filler_todo <= 0) {
       // Apply lowest-priority line attr now, so everything can override it.
       wlv.char_attr = hl_combine_attr(wlv.line_attr_lowprio, wlv.char_attr);
+    }
 
+    if (wlv.filler_todo <= 0) {
       vcol_prev = wlv.vcol;
+    }
 
     // Store character to be displayed.
     // Skip characters that are left of the screen for 'nowrap'.

test/functional/ui/decorations_spec.lua

@@ -4065,6 +4065,8 @@ describe('decorations: virtual lines', function()
       [7] = {foreground = Screen.colors.SlateBlue};
       [8] = {background = Screen.colors.WebGray, foreground = Screen.colors.DarkBlue};
       [9] = {foreground = Screen.colors.Brown};
+      [10] = {bold = true, reverse = true};
+      [11] = {reverse = true};
     }
 
     ns = api.nvim_create_namespace 'test'
@@ -4860,6 +4862,22 @@ if (h->n_buckets < new_n_buckets) { // expand
     ]])
   end)
 
+  it('does not break cursor position with concealcursor #27887', function()
+    command('vsplit')
+    insert('\n')
+    api.nvim_set_option_value('conceallevel', 2, {})
+    api.nvim_set_option_value('concealcursor', 'niv', {})
+    api.nvim_buf_set_extmark(0, ns, 0, 0, { virt_lines = {{{'VIRT1'}}, {{'VIRT2'}}} })
+    screen:expect([[
+                               │                        |
+      VIRT1                    │VIRT1                   |
+      VIRT2                    │VIRT2                   |
+      ^                         │                        |
+      {1:~                        }│{1:~                       }|*6
+      {10:[No Name] [+]             }{11:[No Name] [+]           }|
+                                                        |
+    ]])
+  end)
 end)
 
 describe('decorations: signs', function()