Building Pull Requests
Pull requests are an essential feature of Travis CI. For a project that has testing via Travis CI enabled, whenever a pull request is opened for the project, Travis CI will build it and update a status on the pull request.
How Pull Requests are Tested
When a pull request is opened, Travis CI receives a pull request notification from GitHub. We turn this notification into a build and run it.
During the build, we update the status of the commits to one of:
- a warning that the build is still running.
- that the pull request should be merged with caution because the build failed.
- that the pull request can be merged safely because the build was successful.
Travis CI builds a pull request when it is first opened, and when commits are added to the pull request .
Rather than test the commits that have been pushed to the branch the pull request is from, we test the merge between the origin and the upstream branch. To only build on push events, you can disable Build on Pull Requests from your repository settings.
Pull Requests and Security Restrictions
The most important restriction for pull requests is about secure environment variables and encrypted data.
A pull request sent from a fork of the upstream repository could be manipulated to expose any environment variables. The upstream repository’s maintainer would have no protection against this attack, as pull requests can be sent by anyone with a fork.
Travis CI makes encrypted variables and data available only to pull requests coming from the same repository. These are considered trustworthy, as only members with write access to the repository can send them.
Pull requests sent from forked repositories do not have access to encrypted variables or data.
If your build relies on these to run, for instance to run Selenium tests with BrowserStack or Sauce Labs, your build needs to take this into account. You won’t be able to run these tests for pull requests from external contributors.
To work around this, restrict these tests only to situations where the environment variables are available, or disable them for pull requests entirely.
Here’s an example of how to structure a build command for this purpose:
script: - 'if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then bash ./travis/run_on_pull_requests; fi' - 'if [ "$TRAVIS_PULL_REQUEST" = "false" ]; then bash ./travis/run_on_non_pull_requests; fi'
My Pull Request isn’t being built
If a pull request isn’t built or doesn’t show up in Travis CI’s user interface, that usually means that it can’t be merged. We rely on the merge commit that GitHub transparently creates between the changes in the source branch and the upstream branch the pull request is sent against.
So when you create or update a pull request, and Travis CI doesn’t create a build for it, make sure the pull request is mergeable. If it isn’t, rebase it against the upstream branch and resolve any merge conflicts. When you push the fixes up to GitHub and to the pull request, Travis CI will happily test them.
Travis CI also currently doesn’t build pull requests when the upstream branch is updated. When this happens, GitHub will update the merge commit between the downstream and upstream branch, and send out a notifications. But Travis CI currently ignores this update, as it could lead to a large number of new builds on repositories with lots of pull requests and lots of updates on the upstream branches.