test(statuscolumn): add virt_lines test for filler lines

Ref: neovim#21766.

src/nvim/drawline.c

@@ -2820,7 +2820,7 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool nochange,
  need_showbreak = true;
  }
  if (statuscol.draw) {
- if (row == startrow + 1 || row == startrow + filler_lines) {
+ if (row == startrow + filler_lines + 1 || row == startrow + filler_lines) {
  // Re-evaluate 'statuscolumn' for the first wrapped row and non filler line
  statuscol.textp = NULL;
  } else { // Otherwise just reset the text/hlrec pointers

test/functional/ui/statuscolumn_spec.lua

@@ -2,6 +2,7 @@ local helpers = require('test.functional.helpers')(after_each)
 local Screen = require('test.functional.ui.screen')
 local clear = helpers.clear
 local command = helpers.command
+local exec = helpers.exec_lua
 local eq = helpers.eq
 local eval = helpers.eval
 local meths = helpers.meths
@@ -337,6 +338,29 @@ describe('statuscolumn', function()
  {2: }{1: │}{2: }{1: }aaaaaaaaaaaaaaaaaaaa |
  |
  ]])
+ -- Status column in filler lines is drawn correctly
+ exec([[
+ local ns = vim.api.nvim_create_namespace("ns")
+ vim.api.nvim_buf_set_extmark(0, ns, 4, 0, {
+ virt_lines = {{{"", ""}}, {{"", ""}}, {{"", ""}}}
+ })
+ ]])
+ screen:expect([[
+ {2: }{1: 4│>>}{2: }{1: }aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+ {2: }{1: │}{2: }{1: }aaaaaaaaaaaaaaaaaaaa |
+ {2: }{1: 3│}{0:>!}{2: }{1: }aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+ {2: }{1: │}{2: }{1: }aaaaaaaaaaaaaaaaaaaa |
+ {2: }{1: │}{2: }{1: } |
+ {2: }{1: │}{2: }{1: } |
+ {2: }{1: │}{2: }{1: } |
+ {2: }{1: 2│>>}{0:>!}{1:>>}{0:>!}{1:>>}{0:>!}{1:>>}{0:>!}{1:>> }aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+ {2: }{1: │}{2: }{1: }^aaaaaaaaaaaaaaaaaaaa |
+ {2: }{1: 1│}{2: }{1: }aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+ {2: }{1: │}{2: }{1: }aaaaaaaaaaaaaaaaaaaa |
+ {2:+}{4: 0│}{2: }{4: }{5:+-- 1 line: aaaaaaaaaaaaaaaaa}|
+ {2: }{1: 1│}{2: }{1: }aaaaaaaaaaaaaaaaaaaaaaaaaaa{0:@@@}|
+ |
+ ]])
  end)
 
  it('works with \'statuscolumn\' clicks', function()