nnmaildir nested Maildirs workaround

[Thomas Schneider]

Hello,

I wanted to use Gnus also for reading mails.  For historical reasons, my
Maildirs are nested (e. g. ~/.maildir/work/INBOX/foo/bar/{cur,new,tmp})
and synced to various IMAP servers.  I still wanted to keep the Maildirs
local, and keep my nested structure, but nnmaildir only supports a flat
hierarchy without leading dots (as mbsync would create them).

Long story short, I now have ~/.nnmaildir with a bunch of symlinks
created by the following script.  It could be better, but for now this
does the trick.

---
#!/usr/bin/env python3

import os
import os.path
import sys

try:
    maildir = os.environ['MAILDIR']
except KeyError:
    if os.path.exists(os.path.expanduser('~/.maildir')):
        maildir = os.path.expanduser('~/.maildir')
    elif os.path.exists(os.path.expanduser('~/Maildir')):
        maildir = os.path.expanduser('~/Maildir')
    else:
        print('no maildir found', file = sys.stderr)
        sys.exit(1)

maildirs = {d for d, dirs, _ in os.walk(maildir)
            if 'cur' in dirs} # cur shall be sufficient to make a dir a maildir

nnm = os.path.expanduser('~/.nnmaildir')
if not os.path.exists(nnm):
    os.mkdir(nnm, mode = 0o700)

for d in maildirs:
    n = d[len(maildir) + 1:].replace('/', '.')
    dst = os.path.join(nnm, n)
    if os.path.exists(dst):
        continue
    src_rel = os.path.relpath(d, os.path.dirname(dst))
    os.symlink(src_rel, dst)
---