How to set up branches with different pull/push upstreams

Question

I have a local git repo with two remotes: upstream, the original main repo, and origin, my GitHub fork of it.

I want to create new branches based off of upstream/master, push them to origin for PRs, and periodically pull in new changes from upstream/master.

Is there a way to set up my branches so that this happens by default? I.e.:

$ git checkout -b my-new-branch --some-other-flags
$ git maybe some other command
# branch 'my-new-branch' points to 'upstream/master' and is checked out
# make changes, git commit
$ git push  # pushes to origin/my-new-branch
$ git pull  # pulls from upstream/master

Answer 1

The following seems to work:

git config push.default current && git config remote.pushdefault origin

Then, create branches with git checkout -b new-branch upstream/master.

git push pushes to origin/my-branch, git pull pulls from upstream/master.

---

For branches based on other local branches instead of upstream/master, things seem a bit trickier. I could git config branch.autoSetupMerge always, but then branches would pull from the local branch they started from, not upstream/master. Or I could set the upstream to upstream/master explicitly with -u when creating the branch. I'm not sure which would be more appropriate though.

Another annoyance is that when I checkout a branch with changes, git sometimes tells me:

Your branch is ahead of 'upstream/master' by 7 commits. (use "git push" to publish your local commits)

But A) it's fine that I'm ahead of my upstream, I'm waiting to merge these changes in a PR, and B) more importantly, git push will push to new-branch at origin, not master at upstream.

This doesn't always happen though, so I think there's some other variable I'm missing here.