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

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

Matt Armstrong-3
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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 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --enable-libsystemd --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/27.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/27.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --build
 x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib
 --infodir=/usr/share/info --mandir=/usr/share/man --enable-libsystemd
 --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/27.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/27.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --with-cairo
 --with-x=yes --with-x-toolkit=gtk3 --with-toolkit-scroll-bars
 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs-6jKC2B/emacs-27.1+1=. -fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

Configured features:
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INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF
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Memory information:
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bug#47552: 27.1; cl-defstruct field names matching read-only variables -> bad code

Lars Ingebrigtsen
Stefan Monnier <[hidden email]> writes:

> I'm pretty sure that's the right solution, *but* I don't think it's
> obvious how to get there: `cl-defstruct` defines the constructor
> using `cl-defsubst` and its `&key` arguments, so the `:gcs-gone` keyword
> argument inevitably maps to a `gcs-done` variable by definition of how
> `&key` is supposed to work.

I'm having a hard time following the code in cl-defstruct -- even where
things are actually defined.

But...  Indeed doing this "doesn't work":

(cl-defsubst foo4 (&key gcs-done)
  gcs-done)

(foo4 :foo 1)
-> Debugger entered--Lisp error: (wrong-type-argument numberp nil)

But:

(foo4 :gcs-done 1)
=> 1

Hm...

--
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no