Re: How to define a (derived) minor mode inaccessible to the user

[Marcin Borkowski]

On 2021-01-22, at 16:38, Stefan Monnier <monnier@iro.umontreal.ca> wrote:

>>> The `interactive-form` property is virtually never used.  Instead, the
>>> interactive form is traditionally stored within the function.
>> So how does `execute-extended-command' know what to list, then?
>
> You can use `commandp` to know if it's got an interactive form or not,
> and `interactive-form` (the function) to extract it from a function.
>
>> A cursory look told me that it uses `read-extended-command', which uses
>> `commandp'.  So, how does `commandp' know?  (I'm not well versed in C,
>> but do I guess correctly that it checks the `interactive-form' property,
>> and if nil, it (somehow) looks for `(interactive ...)' in its
>> definition?)
>
> Pretty much, yes (with the extra handling for the cases where the
> function is not a `(lambda ...)` list but a byte-compiled object, or an
> autoloaded function, or a function implemented in C).

OK, thanks.

>>> If you *really* care about hiding the major mode from the user
>>> I suggest you use an "obscure" or "scary" name.
>> Well, the convention is to use two dashes, but how can the end-user (not
>> knowing Elisp and the conventions) know that?
>
> That's indeed the convention for functions.  For commands we don't
> really have a convention for "commands that should be hidden from `M-x".
> We used to prevent completion from revealing obsolete commands.
> It's been reverted recently (to my disappointment), but we could add
> a similar feature for "commands not to be used via M-x" (could be used
> for those commands that only work when bound to a mouse event, for
> example).
>
> Maybe `smex` offers something like that.  When I rewrote
> `execute-extended-command' into Elisp, I hoped that it would encourage
> people to hack on it and add features to it (like this one), but sadly
> it doesn't seem to have had much effect of this kind so far.
>
> We could add some property that holds a predicate function which
> `execute-extended-command' could use to filter out commands which can't
> be used in the current context (e.g. the predicate could check the
> major mode, for those commands which only work in a given major mode).
>
>> So, basically you move the function definition from the function cell to
>> the value cell of `my-mode', right?  Clever!  Is it actually used
>> anywhere in Emacs?
>
> No, and I don't recommend it.
> E.g `C-h m` will then fail to show the proper docstring of the major mode.

I see.  Still interesting.

Thanks,

-- 
Marcin Borkowski
http://mbork.pl