This is mostly copied from a thread in the Community Forum here - https://discuss.circleci.com/t/allow-branch-whitelist-to-override-only-build-pull-requests/6392
The goal is to be able to have Circle automatically build all commits to the default branch *as well as* other specially named branches without having to build non-PR branches. This is very useful for those of us who have expensive steps in our build process (like tests that run on external servers, or those using the mac OS builds who want to save minutes).
Minimum viable here would be to allow a list of branch names. Better would be to allow a list of branch names and/or regexes to specify branches.
We have a work-around that we developed locally by opening up fake PRs from our release branches into master as part of our process. But it's manual, error prone, and inelegant. Supporting a whitelist would be much nicer.