Got a couple weird ones here (hacking article-display-hook)

[Karl Kleinpaste <karl@justresearch.com>]

Colin Rafferty <craffert@ms.com> writes:
> You could probably do something group-local with `gnus-signature-separator'
> and `gnus-article-hide-signature'.

Indeed, yes, and thanx.  Those clues gave me something to work with,
but unfortunately (or fortunately, as the case may be) they led me to
discovering a couple odd bugs.

First -- not a bug specifically, but something of an operational lack
-- what I need is a means to add something to
gnus-article-display-hook on a per-group basis.  That is, I don't want
signature hiding to be done anywhere but one particular group.  This
doesn't seem to exist in any form; trying to do it via either group
properties with `G p' or by adding (local (var form)) in scorefiles
doesn't give the right result: Both end up with buffer-local versions
of gnus-article-display-hook, which are local to the *Summary* buffer,
and seem to have no effect in the *Article* buffer.  I can't even
usefully set gnus-signature-separator via such mechanisms; edebug'ing
through article-hide-signature shows (correctly, I suppose, but
inconveniently) that the unmodified gnus-signature-separator is what's
active in the *Article* buffer.  But I can at least set
gnus-signature-separator globally in .gnus, since its setting doesn't
really conflict with anything elsewhere, and that's fine, I guess.

So, second, I thought I'd try a different approach: Add or remove
signature hiding to the global gnus-article-display-hook, on a
per-group basis:

(setq gnus-select-group-hook
      (function
       (lambda ()
	 (if (string-match "that.bad.mailing.list" gnus-newsgroup-name)
	     (add-hook 'gnus-article-display-hook 'gnus-article-hide-signature t)
	   (remove-hook 'gnus-article-display-hook 'gnus-article-hide-signature))
	 ))

Wretched to look at, but seemingly workable.  And in fact, at first
glance it appears to do the right thing.

However, with this in place, and thus with gnus-article-display-hook
possibly altering slightly with each group entry, I've lost the
ability to get a totally raw article via `C-u g'.

I don't understand this one at all.  I've just spent about 20 minutes
with edebug'ing through gnus-summary-show-article,
gnus-summary-select-article, and friends, trying to figure out what
value of gnus-article-display-hook is in use at what points, and
frankly I just don't get it.  The best understanding I've gotten is
that, at times, gnus-article-display-hook's value is a buffer-local
value of '(gnus-article-hide-signature) all by itself; it doesn't seem
to matter exactly, whether one has invoked `g' with an argument or
not.  The visual cue that something weird has happened is that, when
using `C-u g', though signature hiding isn't done, nonetheless
quotation coloring still happens, and most headers are still hidden.

This affects all groups, once -hide-signature has been added once:
Thereafter, while signature-hiding happens only in the affected group
and nowhere else, I can't get a truly raw article in any group.

--karl