bug#31558: 27.0; `custom-file' settings messed up by Emacs 27

[Michael Albinus]

Drew Adams <drew.adams@oracle.com> writes:

> But when you say "which also use packages checking for
> Tramp", what it really comes down to is being able to
> use the same `custom-file' (which has only stuff that is
> inserted automatically by Emacs) with multiple Emacs
> releases (in this case including Emacs 20).

Yes. But again, we're speaking about "multiple Emacs releases" including
releases prior 22. And I don't believe this is used so much these days.
The recent Tramp itself is backward compatible up to Emacs 24 only.

>> If there were such a possibility I would consider it.
>
> Can we perhaps consider this bug report as a request
> for such an enhancement?

Sure. I keep it open, at least as long we're discussing.

>> But it must already exist for Emacsen < 22;
>
> No, I don't think so.  (But I'm not sure what you mean.)

I mean that if we need another mechanism but ":require 'tramp" in the
defcustom, that mechanism must exist also in such old releases.

> Something like this, for example:
>
> (defcustom tramp-verbose 3
>   "..."
>   :group 'tramp
>   :type 'integer
>   :set (lambda (sym val)
>          (when (require 'tramp nil t)
>            (custom-set-default sym val)))
>   :initialize 'custom-initialize-set)

This results in 

--8<---------------cut here---------------start------------->8---
Loading tramp...
Recursive load: "/net/ford/albinus/src/tramp/lisp/tramp.elc", 
"/net/ford/albinus/src/tramp/lisp/tramp.elc", 
"/net/ford/albinus/src/tramp/lisp/tramp.elc", 
"/net/ford/albinus/src/tramp/lisp/tramp.elc", 
"/net/ford/albinus/src/tramp/lisp/tramp.elc"
--8<---------------cut here---------------end--------------->8---

> I think the defcustom above would fit the bill, and it
> would require no time to implement.  It just sets the
> variable normally, but only if Tramp can first be loaded.
>
> It does nothing is Tramp is not available.
> (boundp 'tramp-verbose) returns nil in that case.
>
> (Am I missing something?)

A working setup? :-)

Well, maybe I try something like this next days, as time permits. And
I'm always willing to test your proposals.

Best regards, Michael.