Run Only Tasks Affected by a PR
As your workspace grows, re-testing, re-building an re-linting all projects becomes too slow. To address this Nx implements code change analysis to determine the minimum set of projects that were affected by the change. How does this work?
nx affected -t <task>
When you run
nx affected -t test, Nx uses Git to determine the files you changed in your PR, it will look at the nature of change (what exactly did you update in those files), and it uses this to determine the list of projects in the workspace that can be affected by this change. It then runs the
run-many command with that list.
For instance, if my PR changes
lib10, and we then run
nx affected -t test, Nx leverages the project graph to determine all the projects that depend on
lib10, marks them as "affected" and runs
test on just that subset of projects.
Visualize Affected Projects
You can also visualize the affected projects using the Nx graph. Simply run:
Specify Which SHAs to Use to Calculate Affected Code
To understand which projects are affected, Nx uses the Git history and the project graph. Git knows which files changed, and the Nx project graph knows which projects those files belong to.
The affected command takes a
head commit. The default
base is your
main branch and the default
head is your current file system. This is generally what you want when developing locally, but in CI, you need to customize these values.
nx affected:build --base=origin/main --head=$PR_BRANCH_NAME # where PR_BRANCH_NAME is defined by your CI system
nx affected:build --base=origin/main~1 --head=origin/main # rerun what is affected by the last commit in main
You can also set the base and head SHAs as env variables:
Typically, you want to set the base SHA not the most recent commit on the
main branch, but rather that latest commit that successfully passed in CI. In other words, in order to be certain that the repo is in a good state, we need to check all the changes that have happened since the last time the repo was in a good state. Depending on your CI provider this might differ:
- Get last successful commit for Azure Pipelines
- Get last successful commit for GitHub Actions
- Get last successful commit for CircleCI
- Get last successful commit for GitLab
- Get last successful commit for Jenkins
Ignoring Files from Affected Commands
Nx provides two methods to exclude glob patterns (files and folders) from
- Glob patterns defined in your
.gitignorefile are ignored.
- Glob patterns defined in an optional
.nxignorefile are ignored.
Not Using Git
If you aren't using Git, you can pass
--files to any affected command to indicate what files have been changed.