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

From: Lars Ingebrigtsen <[email-masked]>
Date: Sun, 04 Apr 2021 22:17:55 +0200

Matt Armstrong <[email-masked]> writes:

> 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?

Using a gensym seems like an obvious solution to me, but perhaps Stefan
has an opinion here (added to the CCs).

-- 
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   bloggy blog: http://lars.ingebrigtsen.no