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

[Eric Abrahamsen]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> My feeling is that we could just remove the addition of the quote
>> character in `eieio-list-prin1'.
>
> Maybe it's needed to distinguish the printed value of "a list that
> starts with the symbol `my-class`" from "an object of class` my-class`"?

Yup.

Clearly this has the potential to turn into a bigger mess. I just pushed
a branch to the repo called "fix/eieio-persistent", based off emacs-26.
I modified Pierre's patch to add more (failing) tests, and then added
another commit which fixes the easy error in handling the return value
of `eieio-persistent-slot-type-is-class-p'.

My feeling is that the process *ought* to be able to handle all the
failing test cases. But even if the issue of quoting is fixed, not all
the tests will pass, as the write/restore process doesn't descend into
lists.

As for the quoting thing, my current idea is to not add quotes to lists
when writing, then strip quotes on restore, if the car of the list is a
valid class symbol then try to restore an object, but wrap in
`condition-case' and return the plain list if an error is raised.

Seems pretty unlikely that someone would write a list that accidentally
happens to restore to a valid object.

Eric