Re: [External] : Re: master 927b885 1/3: Disable filtering of commands in M-x completion

[Juri Linkov <juri@linkov.net>]

>> > (defun foo (&optional beg end)
>> >   (interactive "r")
>> >   (message "FOO"))
>>
>> Yes, I'm sure.  'M-x foo RET' without an active region
>> raises an error:
>>   command-execute: The mark is not active now
>
> I don't see that in Emacs 27.1 or prior (with
> `emacs -Q').  Is this perhaps new for 28?
> If so, why would we do that?

It raises an error because the value of
mark-even-if-inactive was changed to nil,
so the region exists only when explicitly activated.

>> This means that more complex interactive specs
>> need manual tagging using a new tag:
>>   (declare (predicate (use-region-p)))
>
> But even that won't handle arbitrary `interactive'
> sexps, right?

`declare' could use the same logic used in `interactive'
that detects region boundaries.

>> Same tag:
>>   (declare (predicate (not buffer-read-only)))
>
> And what about commands that might be usable
> interactively, but whose `interactive' spec
> doesn't encapsulate all that's involved?  In that
> case, manual addition of a declaration will need
> to look into the logic of the command body as
> well.  (Admittedly, such commands are uncommon.)

Yes, here it should share the same logic as well.

>> Using a prefix arg for 'C-h f' and 'C-h v' to limit the list
>> of completions would be nice.
>>
>> But I guess M-x can't use a prefix arg to limit completions?
>
> Why do you think so?  `C-u M-x describe-function TAB'
> (with my definition from `help-fns+.el') shows only
> commands as candidates.

The docstring of `execute-extended-command' says:

  To pass a prefix argument to the command you are invoking,
  give a prefix argument to ‘execute-extended-command’.

And indeed `C-u M-x forward-char RET' moves 4 chars forwards.
So you can't use `C-u M-x TAB' to limit the number of completions.
Maybe then use another prefix like `C-x', i.e. `C-x M-x'?
This is similar to how `C-x M-:' combines the prefix `C-x'
to run `repeat-complex-command'.