vim-patch:8.0.1748: CmdlineEnter command uses backslash instead of slash

Problem:    CmdlineEnter command uses backslash instead of slash.
Solution:   Don't treat the character as a file name. (closes vim/vim#2837)
a4baf5b325

src/nvim/fileio.c

@@ -6903,7 +6903,13 @@ static bool apply_autocmds_group(event_T event, char_u *fname, char_u *fname_io,
   } else {
     sfname = vim_strsave(fname);
     // Don't try expanding the following events.
-    if (event == EVENT_COLORSCHEME
+    if (event == EVENT_CMDLINECHANGED
+        || event == EVENT_CMDLINEENTER
+        || event == EVENT_CMDLINELEAVE
+        || event == EVENT_CMDWINENTER
+        || event == EVENT_CMDWINLEAVE
+        || event == EVENT_CMDUNDEFINED
+        || event == EVENT_COLORSCHEME
         || event == EVENT_COLORSCHEMEPRE
         || event == EVENT_DIRCHANGED
         || event == EVENT_FILETYPE

src/nvim/testdir/test_autocmd.vim

@@ -840,6 +840,8 @@ func Test_Cmdline()
   au! CmdlineEnter
   au! CmdlineLeave
 
+  let save_shellslash = &shellslash
+  set noshellslash
   au! CmdlineEnter / let g:entered = expand('<afile>')
   au! CmdlineLeave / let g:left = expand('<afile>')
   let g:entered = 0
@@ -852,6 +854,7 @@ func Test_Cmdline()
   bwipe!
   au! CmdlineEnter
   au! CmdlineLeave
+  let &shellslash = save_shellslash
 endfunc
 
 " Test for BufWritePre autocommand that deletes or unloads the buffer.