patch 9.0.0370: cleaning up afterwards can make a function messy

Problem:    Cleaning up afterwards can make a function messy.
Solution:   Add the :defer command.
diff --git a/src/testdir/test_user_func.vim b/src/testdir/test_user_func.vim
index f6e25e3..af05812 100644
--- a/src/testdir/test_user_func.vim
+++ b/src/testdir/test_user_func.vim
@@ -529,4 +529,36 @@
   bw!
 endfunc
 
+func AddDefer(arg)
+  call extend(g:deferred, [a:arg])
+endfunc
+
+func WithDeferTwo()
+  call extend(g:deferred, ['in Two'])
+  for nr in range(3)
+    defer AddDefer('Two' .. nr)
+  endfor
+  call extend(g:deferred, ['end Two'])
+endfunc
+
+func WithDeferOne()
+  call extend(g:deferred, ['in One'])
+  call writefile(['text'], 'Xfuncdefer')
+  defer delete('Xfuncdefer')
+  defer AddDefer('One')
+  call WithDeferTwo()
+  call extend(g:deferred, ['end One'])
+endfunc
+
+func Test_defer()
+  let g:deferred = []
+  call WithDeferOne()
+
+  call assert_equal(['in One', 'in Two', 'end Two', 'Two2', 'Two1', 'Two0', 'end One', 'One'], g:deferred)
+  unlet g:deferred
+
+  call assert_equal('', glob('Xfuncdefer'))
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index 12be156..57b385b 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -2900,4 +2900,19 @@
                '10 RETURN void', instr)
 enddef
 
+def s:OneDefer()
+  defer delete("file")
+enddef
+
+def Test_disassemble_defer()
+  var instr = execute('disassemble s:OneDefer')
+  assert_match('OneDefer\_s*' ..
+        'defer delete("file")\_s*' ..
+        '\d PUSHFUNC "delete"\_s*' ..
+        '\d PUSHS "file"\_s*' ..
+        '\d DEFER 1 args\_s*' ..
+        '\d RETURN\_s*',
+        instr)
+enddef
+
 " vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 0fa74df..c616e18 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -4272,6 +4272,36 @@
   v9.CheckScriptFailure(lines, 'E777', 2)
 enddef
 
+def AddDefer(s: string)
+  g:deferred->extend([s])
+enddef
+
+def DeferTwo()
+  g:deferred->extend(['in Two'])
+  for n in range(3)
+    defer g:AddDefer('two' .. n)
+  endfor
+  g:deferred->extend(['end Two'])
+enddef
+
+def DeferOne()
+  g:deferred->extend(['in One'])
+  defer g:AddDefer('one')
+  g:DeferTwo()
+  g:deferred->extend(['end One'])
+
+  writefile(['text'], 'XdeferFile')
+  defer delete('XdeferFile')
+enddef
+
+def Test_defer()
+  g:deferred = []
+  g:DeferOne()
+  assert_equal(['in One', 'in Two', 'end Two', 'two2', 'two1', 'two0', 'end One', 'one'], g:deferred)
+  unlet g:deferred
+  assert_equal('', glob('XdeferFile'))
+enddef
+
 " The following messes up syntax highlight, keep near the end.
 if has('python3')
   def Test_python3_command()