vim-patch:8.2.2684: not enough folding code is tested

Problem:    Not enough folding code is tested.
Solution:   Add more test cases. (Yegappan Lakshmanan, closes vim/vim#8046)

https://github.com/vim/vim/commit/5c504f680e63120fea36becfabb8d939d4449e34

Reorder test_fold.vim to match upstream.
Cherry-pick Test_fold_expr_error() from patch 8.2.0633.
Cherry-pick syntax feature check from patch 8.2.1432.
Cherry-pick a delete() call from patch 8.2.2112.

3 files changed, 135 insertions, 49 deletions

diff --git a/test/functional/legacy/045_folding_spec.lua b/test/functional/legacy/fold_spec.lua
index 7d7856fd37..a1cfa50880 100644
--- a/test/functional/legacy/045_folding_spec.lua
+++ b/test/functional/legacy/fold_spec.lua
@@ -4,6 +4,8 @@ local Screen = require('test.functional.ui.screen')
 local helpers = require('test.functional.helpers')(after_each)
 local feed, insert, feed_command, expect_any =
   helpers.feed, helpers.insert, helpers.feed_command, helpers.expect_any
+local command = helpers.command
+local exec = helpers.exec
 
 describe('folding', function()
   local screen
@@ -11,7 +13,13 @@ describe('folding', function()
   before_each(function()
     helpers.clear()
 
-    screen = Screen.new(20, 8)
+    screen = Screen.new(45, 8)
+    screen:set_default_attr_ids({
+      [1] = {bold = true, foreground = Screen.colors.Blue},  -- NonText
+      [2] = {foreground = Screen.colors.DarkBlue, background = Screen.colors.LightGrey},  -- Folded
+      [3] = {foreground = Screen.colors.DarkBlue, background = Screen.colors.Grey},  -- FoldColumn
+      [4] = {foreground = Screen.colors.Brown},  -- LineNr
+    })
     screen:attach()
   end)
 
@@ -210,5 +218,96 @@ describe('folding', function()
       Test fdm=indent and :move bug END
       line2]])
   end)
-end)
 
+  -- oldtest: Test_folds_with_rnu()
+  it('with relative line numbers', function()
+    command('set fdm=marker rnu foldcolumn=2')
+    command('call setline(1, ["{{{1", "nline 1", "{{{1", "line 2"])')
+
+    screen:expect([[
+      {3:+ }{4:  0 }{2:^+--  2 lines: ·························}|
+      {3:+ }{4:  1 }{2:+--  2 lines: ·························}|
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+                                                   |
+    ]])
+    feed("j")
+    screen:expect([[
+      {3:+ }{4:  1 }{2:+--  2 lines: ·························}|
+      {3:+ }{4:  0 }{2:^+--  2 lines: ·························}|
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+                                                   |
+    ]])
+  end)
+
+  -- oldtest: Test_foldclose_opt()
+  it('foldclose=all', function()
+    exec([[
+      set foldmethod=manual foldclose=all foldopen=all
+      call setline(1, ['one', 'two', 'three', 'four'])
+      2,3fold
+    ]])
+
+    screen:expect([[
+      ^one                                          |
+      {2:+--  2 lines: two····························}|
+      four                                         |
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+                                                   |
+    ]])
+    feed('2G')
+    screen:expect([[
+      one                                          |
+      ^two                                          |
+      three                                        |
+      four                                         |
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+                                                   |
+    ]])
+    feed('4G')
+    screen:expect([[
+      one                                          |
+      {2:+--  2 lines: two····························}|
+      ^four                                         |
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+                                                   |
+    ]])
+    feed('3G')
+    screen:expect([[
+      one                                          |
+      two                                          |
+      ^three                                        |
+      four                                         |
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+                                                   |
+    ]])
+    feed('1G')
+    screen:expect([[
+      ^one                                          |
+      {2:+--  2 lines: two····························}|
+      four                                         |
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+      {1:~                                            }|
+                                                   |
+    ]])
+  end)
+end)
diff --git a/test/functional/legacy/source_spec.lua b/test/functional/legacy/source_spec.lua
new file mode 100644
index 0000000000..02e6385247
--- /dev/null
+++ b/test/functional/legacy/source_spec.lua
@@ -0,0 +1,31 @@
+local helpers = require('test.functional.helpers')(after_each)
+local Screen = require('test.functional.ui.screen')
+local clear = helpers.clear
+local feed = helpers.feed
+local write_file = helpers.write_file
+
+before_each(clear)
+
+describe(':source!', function()
+  it('gives E22 when scripts nested too deep', function()
+    write_file('Xscript.vim', [[
+    :source! Xscript.vim
+    ]])
+    local screen = Screen.new(75, 6)
+    screen:set_default_attr_ids({
+      [0] = {bold = true, foreground = Screen.colors.Blue},  -- NonText
+      [1] = {background = Screen.colors.Red, foreground = Screen.colors.White},  -- ErrorMsg
+    })
+    screen:attach()
+    feed(':source! Xscript.vim\n')
+    screen:expect([[
+      ^                                                                           |
+      {0:~                                                                          }|
+      {0:~                                                                          }|
+      {0:~                                                                          }|
+      {0:~                                                                          }|
+      {1:E22: Scripts nested too deep}                                               |
+    ]])
+    os.remove('Xscript.vim')
+  end)
+end)
diff --git a/test/functional/ui/fold_spec.lua b/test/functional/ui/fold_spec.lua
index 3c143d87ca..bfa7167100 100644
--- a/test/functional/ui/fold_spec.lua
+++ b/test/functional/ui/fold_spec.lua
@@ -7,7 +7,7 @@ local insert = helpers.insert
 local expect = helpers.expect
 local funcs = helpers.funcs
 local meths = helpers.meths
-local source = helpers.source
+local exec = helpers.exec
 local assert_alive = helpers.assert_alive
 
 
@@ -199,50 +199,6 @@ describe("folded lines", function()
       end
     end)
 
-    it("highlighting with relative line numbers", function()
-      command("set relativenumber cursorline cursorlineopt=number foldmethod=marker")
-      feed_command("set foldcolumn=2")
-      funcs.setline(1, '{{{1')
-      funcs.setline(2, 'line 1')
-      funcs.setline(3, '{{{1')
-      funcs.setline(4, 'line 2')
-      feed("j")
-      if multigrid then
-        screen:expect([[
-        ## grid 1
-          [2:---------------------------------------------]|
-          [2:---------------------------------------------]|
-          [2:---------------------------------------------]|
-          [2:---------------------------------------------]|
-          [2:---------------------------------------------]|
-          [2:---------------------------------------------]|
-          [2:---------------------------------------------]|
-          [3:---------------------------------------------]|
-        ## grid 2
-          {7:+ }{8:  1 }{5:+--  2 lines: ·························}|
-          {7:+ }{9:  0 }{5:^+--  2 lines: ·························}|
-          {1:~                                            }|
-          {1:~                                            }|
-          {1:~                                            }|
-          {1:~                                            }|
-          {1:~                                            }|
-        ## grid 3
-          :set foldcolumn=2                            |
-        ]])
-      else
-        screen:expect([[
-          {7:+ }{8:  1 }{5:+--  2 lines: ·························}|
-          {7:+ }{9:  0 }{5:^+--  2 lines: ·························}|
-          {1:~                                            }|
-          {1:~                                            }|
-          {1:~                                            }|
-          {1:~                                            }|
-          {1:~                                            }|
-          :set foldcolumn=2                            |
-        ]])
-      end
-    end)
-
     it("work with spell", function()
       command("set spell")
       insert(content1)
@@ -1714,7 +1670,7 @@ describe("folded lines", function()
     end)
 
     it('does not crash when foldtext is longer than columns #12988', function()
-      source([[
+      exec([[
         function! MyFoldText() abort
           return repeat('-', &columns + 100)
         endfunction
@@ -1761,7 +1717,7 @@ describe("folded lines", function()
 
     it('work correctly with :move #18668', function()
       screen:try_resize(45, 12)
-      source([[
+      exec([[
         set foldmethod=expr foldexpr=indent(v:lnum)
         let content = ['', '', 'Line1', '  Line2', '  Line3',
               \ 'Line4', '  Line5', '  Line6',