Re: Advicing the `interactive' form of a command

On Sun, May 3, 2026 at 12:03 AM Roland Winkler <[email protected]> wrote:

> The following message is a courtesy copy of an article
> that has been posted to gmane.emacs.help as well.
>
> How can one advice the `interactive' form of a command with advice-add?
> The elisp manual describes the different values for the WHERE argument
> of `add-function' and `advice-add' and how they are equivalent to
> lambda forms.  For example, :around advice is equivalent to
>
>   (lambda (&rest r) (apply FUNCTION OLDFUN r))
>
> This is clear for non-interactive functions.  But what happens
> if I want to modify the interactive form of OLDFUN?
>
> My slightly nontrivial example is `switch-to-buffer' where the
> interactive form depends on `confirm-nonexistent-file-or-buffer'.
> Indeed, the same var affects `switch-to-buffer' and `find-file'.
> So I thought I could fine-tune things with something like
>
>   (setq confirm-nonexistent-file-or-buffer nil) ; for `find-file'
>   (advice-add
>    'switch-to-buffer :around
>    (lambda (fun &rest args)
>      (let ((confirm-nonexistent-file-or-buffer t))
>        (apply fun args))))
>
> But this does not work.  It seems that the `interactive' form of the
> advice'd command `switch-to-buffer' is run outside the let binding.
> Actually, how does the lambda form in the above example work for a command
> if the lambda form does not have an `interactive' form?  I looked into
> nadvice.el, but something like `advice-eval-interactive-spec' is beyond
> my understanding of things.
>

Advising functions, interactive or not, works under lexical scope.  Be sure
you're running your tests in a buffer with lexical binding.  Run the
command elisp-enable-lexical-binding in your test buffer if you're not sure.

The example you gave definitely works for my use cases.  The
"interactivity" of a function is tested by the command loop for the
presence of the 'interactive-form property on the function symbol.  You can
see that property by invoking (interactive-form 'switch-to-buffer).  It
does not impact the advice chain that I've seen.

Separately, as a matter of hygiene, I advise using named functions in hooks
and advice.  You can easily remove them and experiment without trouble.