Inverting a diff or patch || CVS diff

Question

In CVS, my working copy (WC) is on a certain branch (which we'll call "foo"). There have been other changes checked into foo by another dev. I want to do a diff between my WC and the upstream state of foo. Normally, when working in the trunk (HEAD), I just do a cvs diff, and that's fine. But for some reason when doing a plain cvs diff in the branch, the diff is empty. When I try to use "cvs diff -r foo", the diff shows up, but it is inverted -- upstream additions are shown with minuses, and upstream removals are shown with pluses.

How can I either: (1) get CVS to diff "the other way" (plus for upstream additions), or (2) invert a patch (in general)?

Answer 1

You can try export a file from the branch to some temporary file and then make diff between your working copy and this temp file. It seems to be the easiest way.

Answer 2

If the principal purpose of this is to check "what's up" in the central repo, I suggest you get yourselves a functional CVS viewer/browser/web thingy where you can browse and see the latest changes before updating. But assuming all you have is command-line CVS, I will attempt to give you a solution anyway :)

So, what you have here is a branch foo that went from A -> B, where B is the state of the branch (on the server) after the other developer's checkin, and A is the state you last updated your working copy to.

When just doing a plain cvs diff in this situation, you'll see your local changes compared to A since A is what you have checked out. The local CVS state will show that each file comes from the A revision on the foo branch, and when diffing your CVS client will download that revision from the server. In your case I'm guessing you have no local changes since your cvs diff is empty.

Then, when you do a cvs diff -r foo you're diffing your local A (or A+changes) against the server's foo (which currently is at B) - and the changes required to get from the server's B to your A+changes is exactly the opposite of the other developer's check-in, plus your own local changes.

Now, if you really really want to know how B (or tip-of-foo) compares to A (the pristine version of whatever you currently have checked out), what I think you have to do is set a tag on your working copy, then diff that tag against the state of the branch. Something like this:

cvs tag pistos_temp1
cvs diff -r pistos_temp1 -r foo
# And clean up by deleting the tag afterwards:
cvs tag -d pistos_temp1