Homebrew claims it's outdated, except when I try to update

Question

When I run brew doctor I'm told that my brew installation is outdated. Specifically:

~$ brew doctor
Error: Your Homebrew is outdated
You haven't updated for at least 24 hours, this is a long time in brewland!

But when I run update, apparently, all is fine:

~$: brew update
Already up-to-date.

So, I guess all is good? Not so much. brew doctor still tells me my Homebrew is outdated. What gives?

Answer 1

All is good. It's just a bad way of communicating it.

The Homebrew doctor source clearly only checks for the timestamp of your Homebrew repository clone:

if Time.now.to_i - timestamp > 60 * 60 * 24 then <<-EOS.undent
  Your Homebrew is outdated
  You haven't updated for at least 24 hours, this is a long time in brewland!
  EOS
end

It doesn't have any clue about when you really updated or whether there's even a new version available.