GNU bug report logs - #47552
27.1; cl-defstruct field names matching read-only variables -> bad code

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#47552: closed (27.1; cl-defstruct field names matching
 read-only variables -> bad code)
Date: Fri, 23 Jun 2023 15:39:01 +0000

[Message part 1 (text/plain, inline)]

Your message dated Fri, 23 Jun 2023 11:37:53 -0400
with message-id <jwva5wqz175.fsf-monnier+emacs <at> gnu.org>
and subject line Re: bug#47552: 27.1; cl-defstruct field names matching read-only variables -> bad code
has caused the debbugs.gnu.org bug report #47552,
regarding 27.1; cl-defstruct field names matching read-only variables -> bad code
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


-- 
47552: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=47552
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

[Message part 2 (message/rfc822, inline)]

From: Matt Armstrong <matt <at> rfc20.org>
To: bug-gnu-emacs <at> gnu.org
Subject: 27.1; cl-defstruct field names matching read-only variables -> bad
 code
Date: Thu, 01 Apr 2021 11:38:34 -0700

I confirmed this in 27 and 28.

Evaluate these forms in *scratch* or M-x ielm:

    (require 'cl-macs)
    (cl-defstruct a gcs-done)
    (make-a)
    *** Eval error ***  Wrong type argument: numberp, nil

Success is expected, as occurs for structs that don't happen to have
"gcs-done" fields.

The issue is related to the generated code for `make-a', which boils
down to let binding gcs-done to nil:

    (let ((gcs-done)))

Eval the above to get the same error.

Perhaps the code generated for the make- functions should use
make-symbol or gensym instead?  Or a fixed series of field0...fieldN
symbols?  Why risk potentially binding dynamic vars?

For reference, here is how `make-a' is generated.

(defun make-a (&rest --cl-rest--)
    (let* ((gcs-done
	    (car (cdr (plist-member --cl-rest-- ':gcs-done)))))
      (progn
	(let ((--cl-keys-- --cl-rest--))
	  (while --cl-keys--
	    (cond
	     ((memq
	       (car --cl-keys--) '(:gcs-done :allow-other-keys))
	      (setq --cl-keys-- (cdr (cdr --cl-keys--))))
	     ((car (cdr (memq ':allow-other-keys --cl-rest--)))
	      (setq --cl-keys-- nil))
	     (t (error "Keyword argument %s not one of (:gcs-done)"
		       (car --cl-keys--))))))
	(record 'a gcs-done))))


In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.23, cairo version 1.16.0)
 of 2020-11-07, modified by Debian built on x86-ubc-01
Windowing system distributor 'The X.Org Foundation', version 11.0.12010000
System Description: Debian GNU/Linux bullseye/sid

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For information about GNU Emacs and the GNU system, type C-h C-a.

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[Message part 3 (message/rfc822, inline)]

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: Matt Armstrong <matt <at> rfc20.org>, 47552-done <at> debbugs.gnu.org
Subject: Re: bug#47552: 27.1; cl-defstruct field names matching read-only
 variables -> bad code
Date: Fri, 23 Jun 2023 11:37:53 -0400

>     (defmacro slet* (bindings &rest body)
>       (named-let expand ((bindings bindings))
>         (pcase-exhaustive bindings
>           ('() (macroexp-progn body))
>           (`((,var ,exp) . ,bindings)
>            (let ((rest (expand bindings)))
>      	     (if (macroexp--dynamic-variable-p var)
>      	         `(funcall (identity (lambda (,var) ,rest)) ,exp)
>      	       (macroexp-let* `((,var ,exp)) rest)))))))

Not sure we want to expose that to the language, so I turned it into
a function in `cl-macs.el` for use by `cl-defun/defmacro/defsubst/...`
and pushed it to `master`.

I believe this fixes the bug.


        Stefan

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