bug#33140: 27.0.50; `gnus-posting-styles' sees nil ‘message-reply-headers’ variable

[N. Jackson]

I'm trying to set up a Gnus posting style that makes use of the
‘message-reply-headers’ variable, but the behaviour I see indicates that
this variable is always nil (in the context where the posting styles are
evaluated).

It seems (this is a wild guess) that the function
`gnus-configure-posting-styles' that applies the posting styles that
match, and which is called from `message-mode-hook' (I believe), is
called before `message-reply-headers' is set.

Either that, or `gnus-configure-posting-styles' is evaluated in the
context of the wrong buffer (`message-reply-headers' is buffer local to
the *unsent reply...* buffer).

In (info "(gnus)Posting Styles") it says:

   The attribute value can be a string, a function with zero arguments
  (the return value will be used), a variable (its value will be used)
  or a list (it will be ‘eval’ed and the return value will be used). The
  functions and sexps are called/‘eval’ed in the message buffer that is
  being set up. The headers of the current article are available through
  the ‘message-reply-headers’ variable, which is a vector of the
  following headers: number subject from date id references chars lines
  xref extra.

If I am understanding this documentation correctly,
`message-reply-headers' should be available when posting styles are
evaluated.

===

For example, with the following test setting for `gnus-posting-styles',

  (setq gnus-posting-styles
    '((""               ; Catch all posting style.
       (eval (if message-reply-headers
                (message "`message-reply-headers' is set.")
                (message "`message-reply-headers' is not set."))
       )
      )
     )
  )

If I reply to a message in the Gnus summary buffer

  R             ; `gnus-summary-reply-with-original'.

the following message is printed in the echo area:

  `message-reply-headers' is not set.

. But if I then do

  C-h v message-reply-headers RET

(in the new *unsent reply...* buffer), I'm told

  message-reply-headers is a variable defined in `message.el'.
  Its value is
  [0 "Re: Packing of union fields and bool_bf" "Eli Zaretskii <eliz@gnu.org>" 
"Sat, 13 Oct 2018 18:15:25 +0300" "<838t31vpwy.fsf@gnu.org>" nil 0 0 ""]
  Local in buffer *unsent reply to Eli Zaretskii*; global value is nil

  Documentation:
  The headers of the current replied article.
  It is a vector of the following headers:
  [number subject from date id references chars lines xref extra].

  [back]

Am I missing something here, or is the Gnus posting styles functionality broken?

Note: To be fair, the paragraph quoted above from the Gnus manual only
says that `message-reply-headers' can be used for the attribute value;
it doesn't say that it can be used when the "attribute" is `eval'.
However, the following does not work either (no "Cc" header is inserted
in the new message):

  (setq gnus-posting-styles
    '((""               ; Catch all posting style.
       ;; Set the "Cc" header of the new message to the "From"
       ;; address of the replied-to message.
       (Cc (elt message-reply-headers 2))
       )
      )
     )
  )

but evaluating `(elt message-reply-headers 2)' in the new *unsent
reply...* buffer gives a good value, and furthermore (just to narrow
down where the problem is), the following works fine (the "Cc" header is
inserted):

  (setq gnus-posting-styles
    '((""               ; Catch all posting style.
       ;; Set the "Cc" header of the new message to the "From"
       ;; address of the replied-to message.
       (Cc "john.doe@example.com")
       )
      )
     )
  )

.


In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.26)
 of 2018-10-24 built on moondust.localdomain
Repository revision: 00027ff9d0f646662458bdb47cc7e2214f439698
Windowing system distributor 'Fedora Project', version 11.0.11906000
System Description: Fedora 27 (Workstation Edition)

Configured using:
 'configure 'CFLAGS=-O3 -g3 -gdwarf-4''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS GLIB NOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE LIBOTF XFT ZLIB
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Important settings:
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Major mode: Summary

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Memory information:
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