vim-patch:8.2.2524: cannot change the characters displayed in the foldcolumn

Problem:    Cannot change the characters displayed in the foldcolumn.
Solution:   Add fields to 'fillchars'. (Yegappan Lakshmanan, Matthieu Coudron,
            closes vim/vim#7860)
3aca5a6fbc

src/nvim/testdir/setup.vim

@@ -5,7 +5,7 @@ if exists('s:did_load')
   set directory&
   set directory^=.
   set display=
-  set fillchars=vert:\|,fold:-
+  set fillchars=vert:\|,foldsep:\|,fold:-
   set formatoptions=tcq
   set fsync
   set laststatus=1

src/nvim/testdir/test_display.vim

@@ -309,6 +309,60 @@ func Test_eob_fillchars()
   close
 endfunc
 
+" Test for 'foldopen', 'foldclose' and 'foldsep' in 'fillchars'
+func Test_fold_fillchars()
+  new
+  set fdc=2 foldenable foldmethod=manual
+  call setline(1, ['one', 'two', 'three', 'four', 'five'])
+  2,4fold
+  " First check for the default setting for a closed fold
+  let lines = ScreenLines([1, 3], 8)
+  let expected = [
+        \ '  one   ',
+        \ '+ +--  3',
+        \ '  five  '
+        \ ]
+  call assert_equal(expected, lines)
+  normal 2Gzo
+  " check the characters for an open fold
+  let lines = ScreenLines([1, 5], 8)
+  let expected = [
+        \ '  one   ',
+        \ '- two   ',
+        \ '| three ',
+        \ '| four  ',
+        \ '  five  '
+        \ ]
+  call assert_equal(expected, lines)
+
+  " change the setting
+  set fillchars=vert:\|,fold:-,eob:~,foldopen:[,foldclose:],foldsep:-
+
+  " check the characters for an open fold
+  let lines = ScreenLines([1, 5], 8)
+  let expected = [
+        \ '  one   ',
+        \ '[ two   ',
+        \ '- three ',
+        \ '- four  ',
+        \ '  five  '
+        \ ]
+  call assert_equal(expected, lines)
+
+  " check the characters for a closed fold
+  normal 2Gzc
+  let lines = ScreenLines([1, 3], 8)
+  let expected = [
+        \ '  one   ',
+        \ '] +--  3',
+        \ '  five  '
+        \ ]
+  call assert_equal(expected, lines)
+
+  %bw!
+  set fillchars& fdc& foldmethod& foldenable&
+endfunc
+
 func Test_display_linebreak_breakat()
   new
   vert resize 25