Comment 1 for bug 65265

This is a common requirement for Launchpad development. The question I often want to answer is, what changes will I be responsible for merging... what code do I need to get reviewed.

Generally, I'll start off working on some code by branching mainline, doing some work, and then sending the diff between mainline and my work off to a reviewer to approve it.

The tricky thing is that while I've been working, other people have been landing changes on mainline, so mainline is a moving target. So, to get an accurate idea of what changes I'm proposing to merge, I need to merge mainline into my branch, resolve any conflicts, and then get a diff between my new mainline, and the mainline I just merged into my branch, and send that off to a reviewer.

Also, I want to see this diff myself, as I want to be very aware of what work I'm contributing to the mainline. This is moving my sense of responsibility and ownership away from "I have written this code" in the direction of "I want to improve this common endeavour". The empasis is not on the work I have done, but on the changes I propose to make to the common property.

When I ask for the diff, I don't want a diff against the current mainline, because that may have changed since I merged from it. I want to diff against the mainline I merged from.