The filenames generated by the “Create Patch” button are hashes, which are not sortable or particularly useful. I’d suggest something like this: issue-{number}-{sequential patch number}.diff
If it’s not possible to generate sequential patch numbers, then a timestamp could do.
As a consequence of that change, if somebody presses the "create patch" button again and again, it would create a new patch each time. Currently, it finds that it already has a patch for a given revision, and aborts.
Adding the first few chars of the revision to the filename might solve that problem.
Even 3-4 chars should be enough if we want to keep the name short.
I’m okay for issue-{number}-{sequential patch number}-{first 6 chars of changeset id}.diff (the sequential number for human sorting, the 6 hex chars as unique identifier (the number 6 comes from a chat with Mercurial devs)).