incomplete: find more labels, that is, check all labels, and list the ones that have more than 0, or list the top 4 or 5, depending on space.
don't list labels which have a count of 0

A few comments:

• In your pad it seems to be issue 26
• Issue 26 mentions thread-index-mode, but you're doing this for inbox-mode. I'd prefer it stay in inbox-mode only as you did here, I don't like when there is too much clutter that doesn't provide meaning
• Speaking of which, starred and unread are enough for me (if I want a count of threads with label X, I can always list labels)

@rakoo thanks for comments. i will improve that. unfortunately enumeration in factor.cc gets broken :/

@eMBee please tell what do you think about @rakoo suggestions.

@rakoo i think you missread the number, 26 is something different entirely.
i'd like the numbers for every list of messages, and the idea of counting other labels is this:
say you have labels sup,family, work,important,urgent
when looking at the work messages, how many work messages are labelled important and how many urgent?
so it is not the total count of labels, but the count messages labeled work and that label.

Oh, I understand, it will be only a count of labels for threads that match your current view. I thought it was for all threads. The code currently checks for all threads, that's why I was thinking the other one.

Yes, it's an interesting feature. I don't know about the order of labels you want to display then, but I guess starred and unread are good as first labels.

the order by count, so list the most used ones first, or by age, list the newest ones first, but that might be tricky