Make cabal check warn if copyright field doesn't have current year

[bos]

(Imported from Trac #790, reported by guest on 2011-01-15)

Quite a few packages being uploaded on Hackage have 2010 as the copyright year, probably because developers forgot to update the year. As an example, see http://hackage.haskell.org/package/turni-2011.1.15 which was uploaded in 2011, but puts the copyright as 2010 (that's just the first I encountered, but there are loads).

I suggest cabal check should warn if copyright doesn't have the current year in the field.

[bos]

(Imported comment by @BenMachine on 2011-01-15)

Copyright fields can in general contain an arbitrary string (or frequently, no string at all) so I imagine it being tricky to parse a year out of it reliably unless we also standardised the format. Think about things like (c) 2006-9 John Smith, 2009-10 Martha Jones.
Plus there are plenty of packages that aren't the original work of the uploader (e.g. forks, maintainerships, cabalizations, etc.), in which case it might be inappropriate to update the copyright field.