I also would love to see this feature. Building on a push is great, but I also want to build on the merge commit that GitHub creates for every pull request (i.e. the head of the pr/<pull_request_id>/merge branch that GitHub creates). I understand it results in more load on CircleCI’s servers, but it seems important to test the actual result of merging a pull request, and not just the commit itself (which might be tens or hundreds of commits behind the target branch). There’s a real risk that even without merge conflicts, the tests may pass for the commit but fail once it is merged.
Additionally, I need this functionality in order to support a downstream build system I’ve pieced together using CircleCI’s experimental build parameters on their API. Without it, the process will only work if another push is made to the PR after it is opened.
It looks like this functionality has also been requested in several other threads:
https://discuss.circleci.com/t/show-test-results-for-prospective-merge-of-a-github-pr/1662
Also related:
https://discuss.circleci.com/t/feature-request-option-to-disable-builds-on-commit-pushes/682