[Dovecot] LIST command ignores "hidden=yes" for default namespace

[Bill Boebel]

I'm not sure if this is a bug or just an undesirable feature, but when I
have our namespace configured to match Courier's "INBOX." functionality,
Dovecot forces me to also define a default namespace (with no prefix). 
Without the default namespace defined I get "NO Unknown namespace." errors
when trying to subscribe or unsubscribe folders.

So I have configured my namespaces like this:

namespace private {
  separator = .
  prefix = INBOX.
  inbox = no
}
namespace private {
  separator = .
  prefix =
  inbox = yes
  hidden = yes
}

However with this configuration, LIST commands ignore the "hidden = yes"
setting on the default namespace and IMAP clients end up displaying an
identical folder listing twice...

2 list "" "*"
* LIST (\HasChildren) "." "INBOX"
* LIST (\HasNoChildren) "." "INBOX.spam"
* LIST (\HasNoChildren) "." "INBOX.Trash"
* LIST (\HasNoChildren) "." "INBOX.Sent"
* LIST (\HasNoChildren) "." "INBOX.Drafts"
* LIST (\HasNoChildren) "." "INBOX.RSS"
* LIST (\HasNoChildren) "." "INBOX.test"
* LIST (\HasNoChildren) "." "INBOX.test2"
* LIST (\HasNoChildren) "." "spam"
* LIST (\HasNoChildren) "." "Trash"
* LIST (\HasNoChildren) "." "Sent"
* LIST (\HasNoChildren) "." "Drafts"
* LIST (\HasNoChildren) "." "RSS"
* LIST (\HasNoChildren) "." "test"
* LIST (\HasNoChildren) "." "test2"
2 OK List completed.

Again, I am not sure if this was intended, but either way it is
undesirable for us.  I even had a couple customers delete one of their
duplicate folders thinking that was safe, but it deleted both folders - of
course.

To force Dovecot to hide mailboxes in the default namespace I made the
following change:

src/imap/cmd-list.c:
@247
+	if (ns->hidden) {
+		return;
+	}