(see also [wiki:PatchReviewProcess How To Review Patches])

Please create a new ticket to track the issue unless your patch is a patch for an issue that is already ticketed.

Then run the following darcs commands to generate a darcs patch file named {{{WHAT.txt}}}:

{{{
  darcs record
  darcs send -o WHAT.dpatch
}}}

And attach it to the ticket.

Please use a filename like *.dpatch (instead of *.patch or *.diff) so that Trac will display it 
with syntax highlighting instead of requiring people to download it to see it.

If you don't have darcs just attach a normal old unified diff.