web UI doesn't allow comparison between versions of a PR branch

[aspiers]

When you want to amend a pull request, you have a choice of two ways to do it:

1. Push new commits on top of the head of the existing PR branch
2. Force-push (git push -f) a new head to the PR branch, thereby rewriting history.

Unfortunately currently both have significant problems, as explained in this issue's siblings #997.

This issue is for tracking just one of the problems with the second (force-push) approach: if you amend PR branches via force-push, there is no way in the web UI to see the difference between the versions of the PR. (#997 and #998 document other, separate problems with this approach.)

This is in stark contrast to Gerrit which preserves every version of a patch set for every review.

There is a workaround but it is even less convenient than the workaround for #998, since you first have to use that workaround, and then use a standard approach for comparing two branches, either on the CLI or in your git-enabled IDE, or via GitHub's comparison feature.

[jd]

This is a major frustration for us coming from Gerrit. We have some reviewers complaining about that unfortunately.

One of my idea currently to workaround that limitation is to add a feature in https://github.com/jd/git-pull-request that would send a diff as a comment when the branch is push -f. It'd really be a poor solution, but might be better than nothing. :(

[aspiers]

That's a nice idea! We could also build a tool (or better, extend an existing one such as your git-pull-request, or hub or git-spindle or git-repo) to automate extracting the heads of previous versions of the PR from the API. They could be stored in git refs using a very similar naming scheme to what git review -d uses. Then comparison would be reduced to a simple git diff or similar.

[aspiers]

I just discovered that GitLab has had this since 2016.

[aspiers]

Thanks to @KaelWD for noting that force pushes are now shown in the PR history:

This was also announced in GitHub's Changelog, albeit with very few details given.

When clicking on the "force-pushed" hyperlink, it takes you to a diff between the "before" and "after". So this is a great step in the right direction! However, comparing non-adjacent versions of the PR still requires manually altering the .../compare/BEFORE..AFTER URL. So GitHub still has some work to do before it reaches parity with Gerrit.

[flin-8]

Microsoft TFS does this quite well, you can see the combined changes or individual updates (whether force pushed or not)

https://docs.microsoft.com/en-us/azure/devops/repos/git/pull-requests?view=azure-devops

[cirosantilli]

The SO question: https://stackoverflow.com/questions/39684749/compare-old-and-new-versions-of-force-pushed-github-pull-request