Make pull request info available as a Pipeline Value
Currently, you can get pull request info from environment variables such as
CIRCLE_PULL_REQUEST , but these variables are only available in the context of a job. It would be useful for this info to be available in a Pipeline Value as well so that it could be used as part of conditional workflows. For example, I want to run some simple checks on every commit, but I only want to run my full test suite on pull requests. If I could determine the presence of a pull request using a pipeline value, I could run my test workflow conditionally without resorting to hacks such as halting a job. The pipeline values list already contains a namespace for Git related values such as
pipeline.git.branch, so there is precedent for a change such as this.