RE: always put Customizations in `custom-file', never in `user-init-file'

["Drew Adams" <drew.adams@oracle.com>]

> Well, it's embarrassing to admit, but we really screwed up.  Keeping a
> backup of the original .emacs should have been enough.

I don't know if it's sufficient, but it's necessary.

> We didn't.
> The thing to be aware of, is that after aborting due to an error,
> there are no customizations known to customize, but users will often
> save a few customizations so that they can get some work done.

I'm not sure I follow completely. Could you run down such a scenario,
including when the error occurred? During which Emacs session: before,
during, or after migration, and when during the session?

> This will then destroy the customization file (at least in our version
> of customize) since a custom-save simply writes out the whole state.
> Custom has some protection against doing this automatically, I think,
> but the migration code wasn't aware of it, and neither were users.
> Ooops!  Tricky, very tricky.
>
> The other thing to note is that this was typically reported by people
> using Emacs and trying XEmacs.  Normally you don't have errors in your
> init file. :-)
>
> I think separate custom-file and automigration are both good ideas.

Let's try to find a safe way to do it, then.

> Just be aware that (at least in our implementation of custom, but I
> think it's probably true of Emacs's, too) there are some ways to go
> badly wrong, and be careful to protect the user's init file and
> existing customizations.
>
>  > Yes, you are of course right.
>
> In hindsight, yes, but we had to learn that from experience.  The
> experience is there, I'd like you to benefit from it.

Thanks for reporting the experience. It sounds to me like the potential
gotchas could be handled OK, but it would be good for someone more expert in
this area to comment. And yes, we should proceed with any such change
carefully.