ci: enable commitlint for PRs

.commitlint.config.mjs

@@ -0,0 +1,42 @@
+/* [commitlint](https://github.com/conventional-changelog/commitlint) configuration */
+import {
+    RuleConfigSeverity,
+} from '@commitlint/types';
+
+export default {
+    parserPreset: 'conventional-changelog-conventionalcommits',
+    rules: {
+        'header-max-length': [RuleConfigSeverity.Error, 'always', 72], // Header should be 72 characters or shorter
+        'header-trim': [RuleConfigSeverity.Error, 'always'], // No leading/trailing whitespace in header
+        'subject-empty': [RuleConfigSeverity.Error, 'never'], // No empty subject
+        'subject-case': [ // Subject line should be lowercase
+            RuleConfigSeverity.Error,
+            'never',
+            ['sentence-case', 'start-case', 'pascal-case', 'upper-case']],
+        'subject-full-stop': [RuleConfigSeverity.Error, 'never'], // No full-stop at end of subject
+        'body-max-line-length': [RuleConfigSeverity.Error, 'always', 72], // Body lines should be 72 characteres or shorter
+        'body-leading-blank': [RuleConfigSeverity.Error, 'always'], // Empty line before body
+        'type-empty': [RuleConfigSeverity.Error, 'never'], // Commit type must be present
+        'type-case': [RuleConfigSeverity.Error, 'always', 'lower-case'], // Commit type should be lowercase
+        'type-enum': [ // Commit type allowlist
+            RuleConfigSeverity.Error,
+            'always',
+            [
+                'build',
+                'chore',
+                'ci',
+                'docs',
+                'feat',
+                'fix',
+                'perf',
+                'refactor',
+                'revert',
+                'style',
+                'test',
+            ],
+        ],
+    },
+    ignores: [
+        (message) => message.includes("Merge pull request #"), // PR merges are allowed
+    ],
+};

.github/workflows/commitlint.yml

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+name: Lint Commit Messages
+on:
+  pull_request:
+    types:
+      - opened
+      - edited
+      - reopened
+      - synchronize
+
+jobs:
+  commitlint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Setup Node
+        uses: actions/setup-node@v4
+      - name: Install dependencies
+        run: npm install commitlint @commitlint/config-conventional
+      - name: Run commitlint against commits in PR
+        run: |
+          npx commitlint \
+            -g ${{ github.workspace }}/.commitlint.config.mjs \
+            --from ${{ github.event.pull_request.base.sha }} \
+            --to ${{ github.event.pull_request.head.sha }} \
+            --help-url="https://github.com/${GITHUB_REPOSITORY}/blob/${GITHUB_BASE_REF}/CONTRIBUTING.md" \
+            --verbose