[Dovecot] maildir rename_subfolders() and listescape interaction

[pod]

I'd like to flag a problem we are observing that looks like it is caused
by the listescape-plugin.c.  I realize that this plugin is not part of the
standard Dovecot 1.0 distribution but I would appreciate any insights or
suggestions for fixes that anyone is kind enough to offer.

The problem concerns subfolder renames when used in conjunction with
Maildir folders (I've not tested this against any other folder type).

Without listescape plugin:

    mail_location: maildir:%h/Maildir:INDEX=%h/index:CONTROL=%h/control
    mail_plugins(default): quota imap_quota
    mail_plugins(imap): quota imap_quota
    namespace:
      type: private
      separator: /
      inbox: yes

01 LIST "" *
* LIST (\HasNoChildren) "/" "INBOX"
01 OK List completed.
02 CREATE a
02 OK Create completed.
03 CREATE a/b
03 OK Create completed.
04 LIST "" *
* LIST (\HasChildren) "/" "a"
* LIST (\HasNoChildren) "/" "INBOX"
* LIST (\HasNoChildren) "/" "a/b"
04 OK List completed.
05 RENAME a c
05 OK Rename completed.
06 LIST "" *
* LIST (\HasChildren) "/" "c"
* LIST (\HasNoChildren) "/" "INBOX"
* LIST (\HasNoChildren) "/" "c/b"
06 OK List completed.
07 LOGOUT
* BYE Logging out
07 OK Logout completed.

With listescape plugin:

    mail_location: maildir:%h/Maildir:INDEX=%h/index:CONTROL=%h/control
    mail_plugins(default): quota imap_quota listescape
    mail_plugins(imap): quota imap_quota listescape
    namespace:
      type: private
      separator: /
      inbox: yes

01 LIST "" *
* LIST (\HasNoChildren) "/" "INBOX"
01 OK List completed.
02 CREATE a
02 OK Create completed.
03 CREATE a/b
03 OK Create completed.
04 LIST "" *
* LIST (\HasChildren) "/" "a"
* LIST (\HasNoChildren) "/" "INBOX"
* LIST (\HasNoChildren) "/" "a/b"
04 OK List completed.
05 RENAME a c
05 NO Internal error occurred. Refer to server log for more information. [2007-08-30 19:33:41]
06 LIST "" *
* LIST (\HasNoChildren) "/" "a/b"
* LIST (\HasNoChildren) "/" "c"
* LIST (\HasNoChildren) "/" "INBOX"
06 OK List completed.
07 LOGOUT
* BYE Logging out
07 OK Logout completed.

Seemingly the only relevant log entry is

@4000000046d70d8f1f72b66c dovecot: Error: IMAP(pod): rename(/srv/mail/home/test0/pod/Maildir/.a/b, /srv/mail/home/test0/pod/Maildir/.c/b) failed: No such file or directory

Note the response to tag 05 in each case.  The 06 list response in the
listescape case is not unexpected given the nature of the failure.

My initial reading of rename_subfolders() from maildir-storage.c suggests
that the calls through maildir_mailbox_list_init() and
maildir_mailbox_list_next() are returning "external" style names
(i.e. ones that present "/" as the hierarchy separator) to
rename_subfolders(), which is an "internal" helper function.  This is
supported by the logged error message.

I am afraid I am yet to get my head around the actual code path and the
escaping and unescaping that is going on so am not able to suggest a fix
as yet.