bazel-action

Note: This repository is currently in a Work In Progress state. We will publicize information about its proper usage when it is ready.

Provides a GitHub Action for computing, uploading, and testing bazel targets. Functions as an extension to the Trunk Merge GitHub Action. To get beta access to the Merge Graph, contact us on Slack.

Overview

Using impacted targets lets you only test what you need to test, saving CI time and money! Use this action to upload targets to the Trunk MergeGraph or to run tests on impacted targets directly, or both!

Trunk’s MergeGraph keeps your main branch green by ensuring that tests pass prior to merging your main branch. The MergeGraph, unlike traditional MergeQueues, increases throughput by only testing dependent PRs; no more waiting for your backend changes to test before landing your docs!

How the MergeGraph Works

After creating a MergeGraph at app.trunk.io, simply comment /trunk merge on your PRs to submit it to the graph. Once the graph has passed the prerequisites to be admitted into the graph (impacted targets have been uploaded, Github deems the PR mergeable), the Trunk Service will en-graph the PR, constructing a test branch between the PR and all of its ancestors. On successful completion of tests, Trunk merges the PR, keeping your main branch green 😎.

Usage

name: Upload and Test Impacted Targets
on: pull_request

jobs:
  impacted_targets:
    name: Impacted Targets
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v3

      - name: Upload and Test Impacted Targets
        uses: trunk-io/bazel-action@v1
        with:
          ### To upload targets (default false)
          upload-targets: "true"
          ### To run tests (default true)
          test-targets: "true"
          ### Use your repositories API token to authenticate impacted targets uploads.
          trunk-token: ${{ secrets.TRUNK_REPO_API_TOKEN }}

Tests

pnpm install
pnpm test

What is an Impacted Target?

An impacted target is a unit that is affected by a particular PR. For example, a change at src/backend/app will impact the Bazel src/backend package. Any two pull requests that share an impacted target must be tested together; otherwise, they can be tested independently.

The impacted targets for uploading to MergeGraph and for testing may necessarily be different. When running tests on pull requests, the diff must be calculated between the PR branch and the merge-base of HEAD and the target. However, when uploading targets, the target's HEAD must be used in order to keep up to date with what has merged.

We currently support Bazel; other solutions, such as Buck, Nx, etc. are on the way! You may also define your own suite of impacted targets using glob-based targets.

Under the hood: Bazel

We use Tinder's bazel-diff tool to compute the impacted targets of a particular PR. The tool computes a mapping of package --> hash at the source and dest shas, then reports any packages which have a differing hash.