patch 9.1.0741: No way to get prompt for input()/confirm()

Problem:  No way to get prompt for input()/confirm()
Solution: add getcmdprompt() function (Shougo Matsushita)
          (Shougo Matsushita)

closes: #15667

Signed-off-by: Shougo Matsushita <Shougo.Matsu@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 3f6918a..17717d2 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -1617,7 +1617,7 @@
 
 set cpo&
 
-func Test_getcmdtype()
+func Test_getcmdtype_getcmdprompt()
   call feedkeys(":MyCmd a\<C-R>=Check_cmdline(':')\<CR>\<Esc>", "xt")
 
   let cmdtype = ''
@@ -1641,6 +1641,20 @@
   cunmap <F6>
 
   call assert_equal('', getcmdline())
+
+  call assert_equal('', getcmdprompt())
+  augroup test_CmdlineEnter
+    autocmd!
+    autocmd CmdlineEnter * let g:cmdprompt=getcmdprompt()
+  augroup END
+  call feedkeys(":call input('Answer?')\<CR>a\<CR>\<ESC>", "xt")
+  call assert_equal('Answer?', g:cmdprompt)
+  call assert_equal('', getcmdprompt())
+
+  augroup test_CmdlineEnter
+    au!
+  augroup END
+  augroup! test_CmdlineEnter
 endfunc
 
 func Test_verbosefile()