ex_getln: add secret charm

Opt in to this secret world using

    set wildchar=0
    " already the default, but remove if non-zero existing config:
    set wildcharm=0

now you can map 'wildmode' just like any mode:

    cnoremap <tab> <c-z>
    function! Spacey()
      return getcmdline()[-1:] == "/" ? "\<bs>" : ""
    endfunc
    cnoremap <expr> / wildmenumode() ? Spacey()."/<c-z>" : "/"

Possibly asked questions:

What about backwards compatibility?
====

Just do nothing and your existing 'wildchar' and 'wildcharm' will keep working.

Doesn't `<c-z>` mean suspend?
====

Not in cmdline mode. If it would then the recommended wildcharm would not
have been `<c-z>` to start with.

My config relies on `:<c-z>` being a synonym to `:<nop>`!
====
just no.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index 0100be15bc..ed408c28e5 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -1024,7 +1024,7 @@ static int command_line_execute(VimState *state, int key)
   }
 
   // free expanded names when finished walking through matches
-  if (!(s->c == p_wc && KeyTyped) && s->c != p_wcm
+  if (!(s->c == p_wc && KeyTyped) && s->c != p_wcm && s->c != Ctrl_Z
       && s->c != Ctrl_N && s->c != Ctrl_P && s->c != Ctrl_A
       && s->c != Ctrl_L) {
     if (compl_match_array) {
@@ -1328,7 +1328,8 @@ static int command_line_execute(VimState *state, int key)
   // - hitting <ESC> twice means: abandon command line.
   // - wildcard expansion is only done when the 'wildchar' key is really
   //   typed, not when it comes from a macro
-  if ((s->c == p_wc && !s->gotesc && KeyTyped) || s->c == p_wcm) {
+  if ((s->c == p_wc && !s->gotesc && KeyTyped) || s->c == p_wcm
+      || s->c == Ctrl_Z) {
     int options = WILD_NO_BEEP;
     if (wim_flags[s->wim_index] & WIM_BUFLASTUSED) {
       options |= WILD_BUFLASTUSED;