alt Hacker News> Seems like this is meant to address supporting many different version control systems with a single format.
I'm sorry, this is simply wrong at so many levels. You're lauding this as a solution in search for a problem. As OP pointed out, this is already a solved problem as proven by Git. Git is not using a proprietary format. The problem of "integrate with many other version control systems" depends on whether those version control systems want to work on adding support for this feature. I guarantee you there isn't a single SVN or Mercurial maintainer complaining that they would love to share patches with Git but they are blocked because they cannot implement, let alone design, a format to exchange patches. That is not the hard part. That doesn't even register as a concern.
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>I guarantee you there isn't a single SVN or Mercurial maintainer complaining that they would love to share patches with Git
I was one of those maintainers. So you're already wrong there. As I described in my parent comment, I've worked somewhere this was an actual problem I encountered. I was responsible for both maintaining our SVN repository, and our Review Board instance, so I have had to actually deal with this.
Git is using a proprietary variant on top of Unified Diffs. Unified Diffs themselves convey very little information about the file being modified, focusing solely on the line-based contents of text files and allowing vendors to provide their own "garbage" lines containing anything else. Every SCM that tracks information beyond line changes in a diff fills out the garbage data differently.
The intent here isn't to let you copy changes from one type of repository to another, but to have a format that can be generated from many SCMs that a tool could parse in a consistent way.
Right now, tools working with diffs from multiple types of SCMs need at least one diff parser per SCM (some provide multiple formats, or have significantly changed compatibility between releases.
For SCMs that lack a diff format (there are several) or lack one that contains enough information to identify a file or its changes (there are several), tools also need to choose a method to represent that information. That often means yet another custom diff format that is specific to the tool consuming the diff.
We've spent over 20 years dealing with the headaches and pain points here, giving it a lot of thought. DiffX (which is now a few years old itself) has worked out very well as a solution for us. This wasn't done in a vacuum, but rather has gone through many rounds of discussion with developers at a few different SCM vendors who have given thought to these issues and supplied much valuable feedback and improvements for the spec.