Poll: is ~/.emacs auto-migration worthwhile? Or too dangerous? (was: Re: [PATCH] fix corruption of ~/.emacs when trying to migrate an init file XEmacs can't fully load)

[Stephen J. Turnbull]

SL Baur writes:

 > There are exactly 0 valid usages of it and an apparently infinite number
 > of harmful ones.

Nonsense.  Custom is badly broken in this respect; it simply
overwrites anything it can find, globally.  Most of the time it
doesn't cause any problems, but when there *are* problems the failure
mode is catastrophic.  The point of the automatic migration is to get
people to use a separate ~/.xemacs/custom.el, and apparently it's been
fairly successful.  As a symptom, "Why doesn't my handwritten
(custom-set-something ...)  form DTRT?" used to be a FAQ, now it's
very rare; I've seen it recently, but the time before that was
literally years ago.  Automatic migration was a good idea and still
is.

It is obvious that backing up files that we're going to overwrite is
long overdue ... but Custom still doesn't do that, a tradition of
screwing the user that goes back at least 10 years!  (Which makes an
implementation of auto-migration that depends on `custom-save' to be
safe a criminal act, IMO.  But I've never had time to fix it.)