RFC: solutions for the custom / gnus-xmas-redefine problem

[Didier Verna <didier@lrde.epita.fr>]

        This is something I have raised a very long time ago. Let me just
remind everybody of the problem: when XEmacs is used, the function
`gnus-xmas-redefine' is called, which performs several operations like calling
`add-hook' on many variables.

        The problem is that this function might be called before some gnus
libs are loaded, hence some of these variables are not defcustom'ed. In that
case, the user customizations for such variables are lost. Gnus must hence
ensure that all variables affected by `gnus-xmas-redefine' are properly
defcustomed beforehand.

        What we can do about that is:

1/ Brute force: doing a 'require in `gnus-xmas-redefine' for all libs
defcustom'ing affected variables. This is the simplest solution, but you might
end up with loaded libraries that you're not going to use anyway.

2/ Brute Cleverness: for each concerned gnus lib, create a file
`<lib>-xmas.el' containing the required variables definitions (removed from
the lib itself). Then, both the gnus <lib> and the function
`gnus-xmas-redefine' should do:

| (unless (featurep '<lib>-xmas)
|   (require '<lib>-xmas))

        This is a cleaner solution, but it might not be worth it. Before I
commit anything, I'd like to know if someone has a strong opinion on this.

-- 
    /     /   _   _       Didier Verna        http://www.inf.enst.fr/~verna/
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