[Infrastructure] GitHub Training

Ryan Sleevi sleevi at google.com
Thu Aug 6 15:22:27 MST 2020


On Thu, Aug 6, 2020 at 3:18 PM Ben Wilson <bwilson at mozilla.com> wrote:

> I definitely think Github training would help.  Thanks, Jos.
> For example, I know how to do a "compare" between the main branch and a
> proposed ballot when there aren't that many differences between the two.
> But I ran into trouble today when I tried to do another comparison.  See,
> as example of what an ordinary user like me might encounter:
> https://github.com/cabforum/documents/compare/5f804ccd4a202036a9868d1c43849e43e4c4853d..db4c4af7c01ea815a21bc314fab6cdc4eec7e9f0
>

In the meantime, prior to any training, you should be able to find the
answer at https://wiki.cabforum.org/github_redline_guide . I believe the
cause of your error is addressed at the "2) Your repo is not in sync, and
you can automatically merge" section.

Indeed, with an extra '.' involved, the differences become a little
easier to see: That is, from
https://github.com/cabforum/documents/compare/5f804ccd4a202036a9868d1c43849e43e4c4853d..db4c4af7c01ea815a21bc314fab6cdc4eec7e9f0
 to
https://github.com/cabforum/documents/compare/5f804ccd4a202036a9868d1c43849e43e4c4853d...db4c4af7c01ea815a21bc314fab6cdc4eec7e9f0

The reason for the difference in displays has to do with the common
merge-base: the cabforum/main has added additional changes since you
originally created your branch, and so when you do the "two-dot" compare
using the cabforum/main repository, it's comparing (everything in
cabforum/main since your last branch point) + (everything your branch since
your branch point). The "three-dot" compare instead does (everything in
your branch since your branch point) - that is, it works to find the
"common ancestor" of the commit you specified on the left hand side (the
current cabforum/main) and the commit on the right hand side (your branch),
and then shows what's different in your branch *from that common ancestor*.
This is covered a bit at
https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/about-comparing-branches-in-pull-requests#three-dot-and-two-dot-git-diff-comparisons

Normally, if your branch is in sync with cabforum/main, the two-dot compare
and the three-dot compare are identical, and that's why our wiki says "use
the two-dot compare". That they're different is because of your branch
being a few commits "behind" main. If you follow the steps on the wiki, you
should get back in sync.
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