Suppose you open a file for branch to another place (without submitting), and then reopen it for add and make some edits. I would like to diff this edited version against its branch source in a script.
p4 diff2 is no good because one of the versions is in the client.
p4 diff is no good because it can only diff against the “corresponding” version of the file in the depot, which a branched unsubmitted file doesn’t have yet.
Is there a way, or is the only option to just grab the two files and diff them using a third-party tool?
Sadly, you’re on the money here, you’d need to use a third party diff tool to do this because, as you rightly pointed out, until you’ve submitted the initial integration to the depot, it doesn’t have a copy against which to diff. If you go down this route you’d obviously not be able to access files directly in the depot though, you’d need to have both files on the client PC and specify their paths explicity.