bug#37655: 27.0.50; reversing `gnus-thread-sort-by-most-recent-date' does not work properly

[Eric Abrahamsen]

Hong Xu <hong@topbug.net> writes:

> Reversing `gnus-thread-sort-by-most-recent-date' does not seem to work 
> properly.
>
> To reproduce:
>
> Download the test mbox file from here: 
> https://lists.gnu.org/archive/mbox/bug-gnu-emacs/2000-10 and save it as 
> 2000-10.mbox.
>
> Start Emacs with "-Q", and evaluate the following:
>
>       ;; Latest at bottom
>       (setq gnus-thread-sort-functions
>             '((not gnus-thread-sort-by-most-recent-date)))
>
>       (setq gnus-summary-line-format "%U%R%z %(%&user-date;  %-15,15f  %B 
> %s%)\n")
>
> `M-x gnus', followed by `G f /path/to/2000-10.mbox'. There is only one topic. 
> Type `C-u Enter'.
>
> The summary buffer is supposed to sort the messages in reversed most recent 
> date order in each thread, but a lot of non-compliance can be observed. For 
> instance:
>
>     Oct 02 2000  wm08894@educ.cc  >  (no subject)
>     Oct 12 2000  fujyama yuu        \->
>     Oct 05 2000  bigsuma@home.co   Repost PLEASE HELP or reply!!! please  :)
>     Oct 05 2000  Stefan Reichör    Docstring for kill-line not complete
>
>
> The ``(no subject)'' thread's latest mail is on Oct 12, but ``Docstring for 
> kill-line not complete'' on Oct 05 is positioned after that.

I can reproduce this, but oddly it only seems to have gone wrong for
that one thread -- all the other threads in the mailbox seem to be
sorted correctly. I also note that the Summary buffer displays the date
of both messages in the thread as one day earlier than the Date header
in the message itself. So I wonder if there's just something weird about
one or both of the messages that's causing Gnus to handle the date
incorrectly.

When I have a bit more time I'll try to figure out what date Gnus is
trying to use for that thread.

Eric