bug#41842: 28.0.50; gnus-new-mail-mark is applied to too many groups

[Basil L. Contovounesios]

Severity: minor

I use mbsync to synchronise three remote IMAP inboxes with three local
Maildirs.  I use Dovecot to serve these Maildirs locally over IMAP, each
over a separate connection.  For each local IMAP instance, I add to
gnus-secondary-select-methods a new nnimap entry with a name based on
the corresponding Maildir's basename:

  $ tree -L 1 ~/Mail
  /home/blc/Mail
  ├── outlook
  ├── personal
  └── tcd

gnus-secondary-select-methods:

  ((nnimap "tcd"      ...)
   (nnimap "personal" ...)
   (nnimap "outlook"  ...)
   ...)

I use gnus-topic-mode to organise the subscribed groups of each nnimap
into different topics.  So when mbsync has fetched new mail, and I
either start Gnus, or type g (gnus-group-get-new-news) in an existing
*Group* buffer, I see something like this:

  [ Gnus -- 25888 ]
    [ tcd -- 22671 ]
     %      13?   0! : tcd:INBOX                 13:34
    [ personal -- 79 ]
     %      14?   0! : personal:INBOX            23:27
    [ outlook -- 3 ]
     %       3?   0! : outlook:INBOX            Thu 11

Notice that gnus-new-mail-mark (the % in the fourth column) is on all
three INBOX groups, even though only personal:INBOX contains new mail.

This happens because of the way gnus-group-new-mail in gnus-group.el
checks whether a given group, such as "nnimap+tcd:INBOX", contains new
mail.  It first passes the group name to gnus-group-real-name, which
returns "INBOX", and then passes this result to nnmail-new-mail-p, which
checks for its presence in nnmail-split-history, whose value is
something like:

  ((("INBOX" . 0))
   (("[Gmail].Sent Mail" . 0))
   ...)

Would it be possible for the variable nnmail-split-history, or the
function gnus-group-new-mail, or both, to be changed so they
store/manipulate only the full group name "nnimap+tcd:INBOX"?

Thanks,

-- 
Basil

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version 
1.16.0, Xaw3d scroll bars)
 of 2020-06-13 built on thunk
Repository revision: 4823fa1077e4330bd2574eb54731bb32e6370034
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Debian GNU/Linux bullseye/sid