Juri Linkov <juri@linkov.net> writes:

>>> -    (define-key map "z" 'kill-current-buffer)
>>>      (define-key map "\M-g\M-c" 'switch-to-minibuffer)
>>> +    (define-key map "z" #'completion-kill-buffer)
>>> +    (define-key map [remap keyboard-quit] #'completion-quit)
>>> +    (define-key map [remap quit-window] #'switch-to-minibuffer)
>>
>> It seems that remapping quit-window to switch-to-minibuffer creates
>> issues when the completion buffer is not invoked by the minibuffer, but
>> e.g. by complete-symbol.  Binding it to completion-quit (defined above)
>> instead, might actually be more natural, as "q"/quit-window is expected
>> to close a window.
>
> Good point, so `q' should not be rebound from its standard command
> `quit-window'.  Like you noticed, currently `quit-window' fails
> to select the minibuffer window, but this is a bug, so this regression
> was reported in bug#52491.

Ok, great!

> Then "z" could be bound to a variant of `quit-window'
> that calls it with the argument KILL non-nil.

So something like this?