Upstream branch tracking for git repos was added in https://secure.phabricator.com/D10058. Thus, if I push my local branch (git push --set-upstream origin mybranch) and then try to arc land, it will try to land onto origin/mybranch.
At my organization, we always want to land to master. Eg, arc land --onto master would always be the correct command to run for our use case.
Because developers often keep branches local without pushing them, many aren't in the habit of using --onto master because that is the default behavior. As a result, it is unintuitive for them that something doesn't work when they try to arc land after having pushed their feature branch.
It would be great if there were a way to add some configuration setting to the repo's .arcconfig file that specifies "no, we don't want to land onto the upstream branch -- we always want to land to master" so that developers don't need to remember to always pass the --onto master flag when they push. This would work similar to arc.land.onto.default except it would take precedence over the tracked upstream branch.