Subject: 27.1; cl-defstruct field names matching read-only variables -> bad code
From: Matt Armstrong <[email-masked]>
To: [email-masked]
Date: Thu, 01 Apr 2021 11:38:34 -0700
List-Id: <debbugs-submit.debbugs.gnu.org>

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
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