bug#63513: [PATCH] Make persist-defvar work with records and hash tables

[Eli Zaretskii <eliz@gnu.org>]

> Cc: Adam Porter <adam@alphapapa.net>
> Date: Sun, 14 May 2023 22:56:20 -0700
> From:  Joseph Turner via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> persist-defvar does not persist records or hash tables correctly.
> 
> Here's a minimal example with a hash table:
> 
> (progn
>   (persist-defvar foo (make-hash-table :test #'equal) "docstring")
>   (puthash 'bar t foo)
>   (persist-save 'foo)
>   (gethash 'bar (persist-default 'foo))) ;; Expected nil, got t
> 
> This patch fixes persisting records by using copy-tree. Currently,
> copy-tree does not work with records (see
> <https://lists.gnu.org/archive/html/bug-gnu-emacs/2023-05/msg00875.html>).
> The following snippet will return the expected value only when both this
> patch and the above-linked patch are applied:
> 
> (progn
>   (cl-defstruct baz a)
>   (persist-defvar quux (make-baz :a nil) "docstring")
>   (setf (baz-a quux) t)
>   (persist-save 'quux)
>   (baz-a (persist-default 'quux))) ;; Expected nil, got t
> 
> Before applying this patch, the updated values in both cases are not
> persisted to disk. With the patch, the updated values are persisted as
> expected.

Philip, any comments?