GNU bug report logs - #69521
29.1; Adding a DECLARE spec equivalent to DECLARE-FUNCTION

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Adam Porter <adam <at> alphapapa.net>
To: bug-gnu-emacs <at> gnu.org
Subject: 29.1; Adding a DECLARE spec equivalent to DECLARE-FUNCTION
Date: Sun, 3 Mar 2024 04:49:02 -0600

Hi,

In light of [this thread], this seems like a good time to propose this
idea: to enhance the `declare' form with a `function' spec equivalent to
the top-level `declare-function' form.  This allows keeping the
declaration inside the function that makes it necessary, which has a few
advantages:

1. It clearly indicates which function makes the declaration necessary
   (i.e. which function contains calls to the function in another
   library).
2. If the function is moved to another file, the declaration moves with
   it.
3. If the function is removed, the declaration is removed with it.
4. It reduces the number of top-level forms.

Also, it seems like a natural fit, i.e. `declare-function' to `(declare
(function ...))'.

As an experiment, I implemented this in [Ement] about 10 months ago, and
I've neither seen nor heard of any problems with it.  Here's the code
that implements it:

┌────
│ (eval-and-compile
│   (defun ement--byte-run--declare-function (_name _args &rest values)
│     "Return a `declare-function' form with VALUES.
│ Allows the use of a form like:
│
│   (declare (function FN FILE ...))
│
│ inside of a function definition, effectively keeping its
│ `declare-function' form inside the function definition, ensuring
│ that stray such forms don't remain if the function is removed."
│     `(declare-function ,@values))
│
│   (cl-pushnew '(function ement--byte-run--declare-function) 
defun-declarations-alist :test #'equal)
│   (cl-pushnew '(function ement--byte-run--declare-function) 
macro-declarations-alist :test #'equal))
└────

In use, it looks like this:

┌────
│ (defun ement-notifications--make (notification)
│   "Return an `ement-notification' struct for NOTIFICATION.
│ NOTIFICATION is an alist representing a notification returned
│ from the \"/notifications\" endpoint.  The notification's event
│ is passed through `ement--make-event'."
│   (declare (function ement--make-event "ement"))
│   (pcase-let (((map room_id _actions _ts event read) notification))
│     (make-ement-notification :room-id room_id :readp read
│                              :event (ement--make-event event))))
└────

Would this be an acceptable addition to Emacs Lisp?  If so, I'd be glad
to prepare a patch.

Thanks, Adam


[this thread]
<https://lists.gnu.org/archive/html/emacs-devel/2024-03/msg00057.html>

[Ement] <https://elpa.gnu.org/packages/ement.html>

Message #8 received at 69521 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Adam Porter <adam <at> alphapapa.net>
Cc: 69521 <at> debbugs.gnu.org
Subject: Re: bug#69521: 29.1;
 Adding a DECLARE spec equivalent to DECLARE-FUNCTION
Date: Sun, 03 Mar 2024 13:18:14 +0200

severity 69521 wishlist
thanks

> Date: Sun, 3 Mar 2024 04:49:02 -0600
> From: Adam Porter <adam <at> alphapapa.net>
> 
> In light of [this thread], this seems like a good time to propose this
> idea: to enhance the `declare' form with a `function' spec equivalent to
> the top-level `declare-function' form.  This allows keeping the
> declaration inside the function that makes it necessary, which has a few
> advantages:

Thanks, but I think this should be discussed on emacs-devel first.
The bug tracker is not a good vessel of discussing ideas; in
particular. quite a few of people who should be part of such a
discussion don't read bug-gnu-emacs regularly, and must be explicitly
CC'ed to take notice.

So I suggest to start the discussion on emacs-devel, and only switch
here if/when the idea and its implementation aspects are clear enough
to post a patch.

Thanks.

Message #13 received at 69521 <at> debbugs.gnu.org (full text, mbox):

From: Adam Porter <adam <at> alphapapa.net>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 69521 <at> debbugs.gnu.org
Subject: Re: bug#69521: 29.1; Adding a DECLARE spec equivalent to
 DECLARE-FUNCTION
Date: Sun, 3 Mar 2024 15:04:05 -0600

On 3/3/24 05:18, Eli Zaretskii wrote:

> Thanks, but I think this should be discussed on emacs-devel first.
> The bug tracker is not a good vessel of discussing ideas; in
> particular. quite a few of people who should be part of such a
> discussion don't read bug-gnu-emacs regularly, and must be explicitly
> CC'ed to take notice.
> 
> So I suggest to start the discussion on emacs-devel, and only switch
> here if/when the idea and its implementation aspects are clear enough
> to post a patch.

Ok, I filed the bug report because I had mentioned it in that thread and 
it seemed to get overlooked.  Now I've posted a new thread.  Please see:

https://lists.gnu.org/archive/html/emacs-devel/2024-03/msg00118.html

Message #18 received at 69521 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Adam Porter <adam <at> alphapapa.net>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 69521 <at> debbugs.gnu.org
Subject: Re: bug#69521: 29.1;
 Adding a DECLARE spec equivalent to DECLARE-FUNCTION
Date: Sat, 1 Mar 2025 19:49:40 -0800

Adam Porter <adam <at> alphapapa.net> writes:

> On 3/3/24 05:18, Eli Zaretskii wrote:
>
>> Thanks, but I think this should be discussed on emacs-devel first.
>> The bug tracker is not a good vessel of discussing ideas; in
>> particular. quite a few of people who should be part of such a
>> discussion don't read bug-gnu-emacs regularly, and must be explicitly
>> CC'ed to take notice.
>> So I suggest to start the discussion on emacs-devel, and only switch
>> here if/when the idea and its implementation aspects are clear enough
>> to post a patch.
>
> Ok, I filed the bug report because I had mentioned it in that thread and it
> seemed to get overlooked.  Now I've posted a new thread.  Please see:
>
> https://lists.gnu.org/archive/html/emacs-devel/2024-03/msg00118.html

In that thread, Basil wrote:

    My vote is for instead teaching the compiler to treat
    declare-function more like it treats defvar, in that the effect of
    declare-function should be made local to the current lexical scope.
    [It is already possible to write this way, and I've been known to,
    but sadly the effect is global.]  This wish has been raised and
    agreed on here (at least in passing) before.

    This would reap all the benefits of points 1-4, as well as an
    additional one: that declare-function is lexically closer to the
    implementation through which the need for the declaration arises.  I
    think a declaration at the top of a function is more likely to be
    forgotten and become stale as the implementation changes.

FWIW, I'd very much welcome such a change.

Adam, are you interested in working on that?

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