patch 9.1.1166: command-line auto-completion hard with wildmenu

Problem:  command-line auto-completion hard with wildmenu
Solution: implement "noselect" wildoption value (Girish Palya)

When `noselect` is present in `wildmode` and 'wildmenu' is enabled, the
completion menu appears without pre-selecting the first item.

This change makes it easier to implement command-line auto-completion,
where the menu dynamically appears as characters are typed, and `<Tab>`
can be used to manually select an item. This can be achieved by
leveraging the `CmdlineChanged` event to insert `wildchar(m)`,
triggering completion menu.

Without this change, auto-completion using the 'wildmenu' mechanism is
not feasible, as it automatically inserts the first match, preventing
dynamic selection.

The following Vimscript snippet demonstrates how to configure
auto-completion using `noselect`:

```vim
vim9script
set wim=noselect:lastused,full wop=pum wcm=<C-@> wmnu
autocmd CmdlineChanged : timer_start(0, function(CmdComplete, [getcmdline()]))

def CmdComplete(cur_cmdline: string, timer: number)
  var [cmdline, curpos] = [getcmdline(), getcmdpos()]
  if cur_cmdline ==# cmdline  # Avoid completing each character in keymaps and pasted text
    && !pumvisible() && curpos == cmdline->len() + 1

    if cmdline[curpos - 2] =~ '[\w*/:]'  # Reduce noise by completing only selected characters
      feedkeys("\<C-@>", "ti")
      set eventignore+=CmdlineChanged  # Suppress redundant completion attempts
      timer_start(0, (_) => {
        getcmdline()->substitute('\%x00$', '', '')->setcmdline()  # Remove <C-@> if no completion items exist
        set eventignore-=CmdlineChanged
      })
    endif
  endif
enddef
```

fixes: #16551
closes: #16759

Signed-off-by: Girish Palya <girishji@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 93d612a..ff1b3eb 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -913,6 +913,8 @@
 
     if (wim_flags[wim_index] & WIM_BUFLASTUSED)
 	options |= WILD_BUFLASTUSED;
+    if (wim_flags[0] & WIM_NOSELECT)
+	options |= WILD_KEEP_SOLE_ITEM;
     if (xp->xp_numfiles > 0)   // typed p_wc at least twice
     {
 	// if 'wildmode' contains "list" may still need to list
@@ -958,14 +960,15 @@
 	// when more than one match, and 'wildmode' first contains
 	// "list", or no change and 'wildmode' contains "longest,list",
 	// list all matches
-	if (res == OK && xp->xp_numfiles > 1)
+	if (res == OK
+		&& xp->xp_numfiles > ((wim_flags[wim_index] & WIM_NOSELECT) ? 0 : 1))
 	{
 	    // a "longest" that didn't do anything is skipped (but not
 	    // "list:longest")
 	    if (wim_flags[0] == WIM_LONGEST && ccline.cmdpos == j)
 		wim_index = 1;
 	    if ((wim_flags[wim_index] & WIM_LIST)
-		    || (p_wmnu && (wim_flags[wim_index] & WIM_FULL) != 0))
+		    || (p_wmnu && (wim_flags[wim_index] & (WIM_FULL | WIM_NOSELECT))))
 	    {
 		if (!(wim_flags[0] & WIM_LONGEST))
 		{
@@ -974,7 +977,7 @@
 		    p_wmnu = 0;
 
 		    // remove match
-		    nextwild(xp, WILD_PREV, 0, escape);
+		    nextwild(xp, WILD_PREV, 0 | (options & ~WIM_NOSELECT), escape);
 		    p_wmnu = p_wmnu_save;
 		}
 		(void)showmatches(xp, p_wmnu
@@ -983,7 +986,8 @@
 		*did_wild_list = TRUE;
 		if (wim_flags[wim_index] & WIM_LONGEST)
 		    nextwild(xp, WILD_LONGEST, options, escape);
-		else if (wim_flags[wim_index] & WIM_FULL)
+		else if ((wim_flags[wim_index] & WIM_FULL)
+			&& !(wim_flags[wim_index] & WIM_NOSELECT))
 		    nextwild(xp, WILD_NEXT, options, escape);
 	    }
 	    else
@@ -2716,6 +2720,8 @@
 	    new_wim_flags[idx] |= WIM_LIST;
 	else if (i == 8 && STRNCMP(p, "lastused", 8) == 0)
 	    new_wim_flags[idx] |= WIM_BUFLASTUSED;
+	else if (i == 8 && STRNCMP(p, "noselect", 8) == 0)
+	    new_wim_flags[idx] |= WIM_NOSELECT;
 	else
 	    return FAIL;
 	p += i;