bug#29220: 26.0.90; eieio-persistent-read fail to restore saved object.

[Eric Abrahamsen]

pierre.techoueyres@free.fr (Pierre Téchoueyres) writes:

> Hello Eric,
> Firs, thank you for you fast answer. You fix resolved my first problem
> with eieio-persistent-read, but I've hit another error when I try to use
> complex objects save/restore.  In fact I try to find why pcache package
> insnt working anymore with emacs 26.

Sorry this is so frustrating! And thanks for the very concise recipe.

> So here is the same sample completed. Sorry.
>
> ;;; -*- lexical-binding: t -*-
> (require 'eieio)
> (require 'eieio-base)
>
> (defclass eieio-fail (eieio-persistent eieio-named)
>   ((version :initarg :version :initform nil)
>    (version-constant :allocation :class)
>    (entries :initarg :entries :initform (make-hash-table))))

This problem isn't related to my changes: it looks like the source of
the issue is the way the hash table is written, and the fact that one of
its entries holds an EIEIO object.

As far as I can tell, when the hash table is written with `prin1', the
EIEIO object inside is also getting written with `prin1' instead of
`object-write'. The `prin1' representation isn't readable, so the
persistent read process chokes on it.

The prin1 process for the hash table would have to detect that there's
an object in there, and write it with `object-write'.

I assume this used to work? There have been several changes to the
printing process in Emacs 26, but I don't have a good grasp of the
details -- hopefully Stefan or someone will chime in.

Eric