lighthouse-score-merge-impact

Get pull request merge impact on lighthouse score

Table of contents

• Presentation
• How it works
• Usage in github workflow
• Usage outside github workflow
• Lighthouse report viewer

Presentation

@jsenv/lighthouse-score-merge-impact analyses a pull request impact on lighthouse score. This analysis is posted in a comment of the pull request.

The screenshot below shows that comment posted in a pull request.

The comment can be expanded to get more details.

How it works

In order to analyse the impact of a pull request on lighthouse score this project does the following:

1. Checkout pull request base branch
2. Generates a lighthouse report
3. Merge pull request into its base
4. Generates a second lighthouse report.
5. Analyse differences between the two lighthouse reports
6. Post or update comment in the pull request

Usage in github workflow

You need:

• @jsenv/lighthouse-score-merge-impact in devDependencies
• A file generating a lighthouse report
• The file runned against a pull request
• A workflow.yml

Installation with npm

npm install --save-dev @jsenv/lighthouse-score-merge-impact

lighthouse/generate-lighthouse-report.js

import { createServer } from "http"
import { generateLighthouseReport } from "@jsenv/lighthouse-score-merge-impact"

const server = createServer((request, response) => {
  response.writeHead(200)
  response.end("Hello, World!")
})
server.listen(8080)

generateLighthouseReport("http://127.0.0.1:8080", {
  projectDirectoryUrl: new URL("../", import.meta.url),
  jsonFileRelativeUrl: "./lighthouse/report.json",
})

lighthouse/report-lighthouse-impact.js

import {
  reportLighthouseScoreMergeImpact,
  readGithubWorkflowEnv,
} from "@jsenv/lighthouse-score-merge-impact"

reportLighthouseScoreMergeImpact({
  ...readGithubWorkflowEnv(),
  jsonFileGenerateCommand: "node ./lighthouse/generate-lighthouse-report.js",
  jsonFileRelativeUrl: "./lighthouse/report.json",
})

.github/workflows/lighthouse-impact.yml

name: lighthouse-impact

on: pull_request

jobs:
  lighthouse-impact:
    # Skip workflow for forks because secrets.GITHUB_TOKEN not allowed to post comments
    if: github.event.pull_request.base.repo.full_name == github.event.pull_request.head.repo.full_name
    strategy:
      matrix:
        os: [ubuntu-latest]
        node: [13.12.0]
    runs-on: ${{ matrix.os }}
    name: lighthouse impact
    steps:
        uses: actions/checkout@v2
        uses: actions/setup-node@v1
        with:
          node-version: ${{ matrix.node }}
        run: npm install
      - name: Report lighthouse impact
        run: node ./.github/workflows/lighthouse-impact/report-lighthouse-impact.js
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

Usage outside github workflow

When outside a github workflow you must provide { projectDirectoryUrl, githubToken, repositoryOwner, repositoryName, pullRequestNumber } "manually" to reportLighthouseScoreMergeImpact.

For Travis it would be something as below.

import { reportLighthouseScoreMergeImpact } from "@jsenv/lighthouse-score-merge-impact"

reportLighthouseScoreMergeImpact({
  projectDirectoryUrl: process.env.TRAVIS_BUILD_DIR,
  githubToken: process.env.GITHUB_TOKEN, // make it available somehow
  repositoryOwner: process.env.TRAVIS_REPO_SLUG.split("/")[0],
  repositoryName: process.env.TRAVIS_REPO_SLUG.split("/")[1],
  pullRequestNumber: process.env.TRAVIS_PULL_REQUEST,

  jsonFileGenerateCommand: "node ./lighthouse/generate-lighthouse-report.js",
  jsonFileRelativeUrl: "./lighthouse/report.json",
})

Please note reportLighthouseScoreMergeImpact must be called in a state where your git repository has been cloned and you are currently on the pull request branch. Inside github workflow this is done by the following lines in lighthouse-impact.yml.

uses: actions/checkout@v2
uses: actions/setup-node@v1
with:
  node-version: ${{ matrix.node }}
run: npm install

In your CI you must replicate this, the corresponding commands looks as below:

git init
git remote add origin $GITHUB_REPOSITORY_URL
git fetch --no-tags --prune --depth=1 origin $PULL_REQUEST_HEAD_REF
git checkout origin/$PULL_REQUEST_HEAD_REF
npm install

Lighthouse report viewer

The pull request comment can contain links to see lighthouse reports in Lighthouse Report Viewer.

Every github workflow has access to a magic token secrets.GITHUB_TOKEN. But this token is not allowed to create gists. We need to update ./.github/workflows/lighthouse-impact.yml to use an other token that will have the rights to create gists.

- GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+ GITHUB_TOKEN: ${{ secrets.LIGHTHOUSE_GITHUB_TOKEN }}

You can generate a new token at https://github.com/settings/tokens/new. That token needs repo and gists scope. Copy this token and add it to your repository secrets at https://github.com/REPOSITORY_OWNER/REPOSITORY_NAME/settings/secrets/new. For this example the secret is named LIGHTHOUSE_GITHUB_TOKEN.