Re: Advicing the `interactive' form of a command

Roland Winkler [2026-05-04 10:04:27] wrote:
> On Sun, May 03 2026, Stefan Monnier via Users list for the GNU Emacs text editor wrote:
>> So if you want to apply the let binding to the interactive spec, you
>> can do:
>>
>>     (advice-add 'switch-to-buffer :before
>>       (lambda (&rest _)
>>         (interactive
>>           (lambda (ispec)
>>             (let ((confirm-nonexistent-file-or-buffer t))
>>               (advice-eval-interactive-spec ispec))))
>>         nil))
>
> Thank you, this answers my questions!  Reading the brief discussion of
> advice-eval-interactive-spec (that I had missed previously), I would
> not have guessed that the above two nested lambdas can modify the interactive
> spec of a command.  Maybe one such example can be added to the elisp manual.

Actually, there is already such an example in the manual, where
`advice-eval-interactive-spec` is documented:

    (defun my-compose-mail-advice (orig &rest args)
      "Read From: address interactively."
      (interactive
       (lambda (spec)
         (let* ((user-mail-address
                 (completing-read "From: "
                                  '("one.address@@example.net"
                                    "alternative.address@@example.net")))
                (from (message-make-from user-full-name
                                         user-mail-address))
                (spec (advice-eval-interactive-spec spec)))
           ;; Put the From header into the OTHER-HEADERS argument.
           (push (cons 'From from) (nth 2 spec))
           spec)))
      (apply orig args))
    
    (advice-add 'compose-mail :around #'my-compose-mail-advice)

Eli, what do you think about a patch like the one below?
[ Clearly "See @code{advice-eval-interactive-spec} for an example"
  needs some real xref, but my Texinfo-fu is weak.  ]


=== Stefan


diff --git a/doc/lispref/functions.texi b/doc/lispref/functions.texi
index 5444cea7fa9..c6cedd9346b 100644
--- a/doc/lispref/functions.texi
+++ b/doc/lispref/functions.texi
@@ -2112,7 +2112,7 @@ Core Advising Primitives
 could say something like this:
 
 @example
-(defun my-compose-mail-advice (orig &rest args)
+(defun my-compose-mail-advice (&rest _)
   "Read From: address interactively."
   (interactive
    (lambda (spec)
@@ -2126,9 +2126,10 @@ Core Advising Primitives
        ;; Put the From header into the OTHER-HEADERS argument.
        (push (cons 'From from) (nth 2 spec))
        spec)))
-  (apply orig args))
+  ;; This body is not used.
+  nil)
 
-(advice-add 'compose-mail :around #'my-compose-mail-advice)
+(advice-add 'compose-mail :interactive-only #'my-compose-mail-advice)
 @end example
 @end defun
 
@@ -2148,8 +2149,8 @@ Advising Named Functions
 to named functions, offers the following extra features compared to
 @code{add-function}: they know how to deal with macros and autoloaded
 functions, they let @code{describe-function} preserve the original docstring as
-well as document the added advice, and they let you add and remove advice
-before a function is even defined.
+well as document the added advice, and they let you add and remove
+pieces of advice before a function is even defined.
 
   @code{advice-add} can be useful for altering the behavior of existing calls
 to an existing function without having to redefine the whole function.
@@ -2338,8 +2339,18 @@ Advice Combinators
 @example
 (lambda (&rest r) (funcall @var{function} (apply @var{oldfun} r)))
 @end example
-@end table
 
+@item :interactive-only
+While the @var{where} option controls how the body of the two functions
+are composed, it does not actually affect the way interactive forms are
+composed.  So, in a sense, this does the opposite of @code{:override}:
+call only the old function as if no advice was applied.  But it still
+affects the interactive form like any other @var{where} value would: The
+interactive form of @var{function}, if any, overrides that of
+@var{oldfun} and if it is a lambda expression, it receives
+@var{function}'s interactive form as argument.
+See @code{advice-eval-interactive-spec} for an example.
+@end table
 
 @node Porting Old Advice
 @subsection Adapting code using the old defadvice
diff --git a/lisp/emacs-lisp/nadvice.el b/lisp/emacs-lisp/nadvice.el
index 7421ce079ab..80467caeb40 100644
--- a/lisp/emacs-lisp/nadvice.el
+++ b/lisp/emacs-lisp/nadvice.el
@@ -74,7 +74,8 @@ advice--how-alist
    (:before-until (or (apply car r) (apply cdr r)))
    (:before-while (and (apply car r) (apply cdr r)))
    (:filter-args (apply cdr (funcall car r)))
-   (:filter-return (funcall car (apply cdr r))))
+   (:filter-return (funcall car (apply cdr r)))
+   (:interactive-only (apply cdr r)))
   "List of descriptions of how to add a function.
 Each element has the form (HOW OCL DOC) where HOW is a keyword,
 OCL is a \"prototype\" function of type `advice', and