ci: add commitlint workflow for PR commit messages

.commitlint.config.mjs

@@ -0,0 +1,48 @@
+/* [commitlint](https://github.com/conventional-changelog/commitlint) configuration
+ *
+ * Bottlerocket kit repos use a `scope: description` convention where the scope
+ * is typically a package name (e.g. `kernel-6.12: update to 6.12.94`) or an
+ * area (e.g. `changelog: add release notes for v7.1.0`).
+ *
+ * This differs from standard Conventional Commits which require a fixed type
+ * prefix (feat, fix, etc.). We enforce the structural rules (colon separator,
+ * line lengths, casing) while allowing any lowercase scope before the colon.
+ */
+import { RuleConfigSeverity } from "@commitlint/types";
+
+// Custom plugin to validate the "scope: description" format used in kit repos.
+const kitScopePlugin = {
+  rules: {
+    // Validates that the header matches `lowercase-scope: lowercase description`
+    "kit-scope-format": (parsed, _when, _value) => {
+      const header = parsed.header;
+      // Match: one or more lowercase words/numbers/dots/dashes, colon, space, then description
+      const pattern = /^[a-z][a-z0-9._-]*: .+$/;
+      return [
+        pattern.test(header),
+        "header must match the format 'scope: description' (e.g. 'kernel-6.12: update to 6.12.94')",
+      ];
+    },
+  },
+};
+
+export default {
+  plugins: [kitScopePlugin],
+  rules: {
+    // Structural rules
+    "header-max-length": [RuleConfigSeverity.Error, "always", 72],
+    "header-trim": [RuleConfigSeverity.Error, "always"],
+    "body-max-line-length": [RuleConfigSeverity.Error, "always", 72],
+    "body-leading-blank": [RuleConfigSeverity.Error, "always"],
+
+    // Subject rules (applied to text after the colon)
+    "subject-full-stop": [RuleConfigSeverity.Error, "never", "."],
+
+    // Custom kit scope format
+    "kit-scope-format": [RuleConfigSeverity.Error, "always"],
+  },
+  ignores: [
+    (message) => message.includes("Merge pull request #"),
+    (message) => message.startsWith("Revert \""),
+  ],
+};

.github/workflows/commitlint.yml

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+name: Lint Commit Messages
+
+on:
+  pull_request:
+    types:
+      - opened
+      - edited
+      - reopened
+      - synchronize
+
+jobs:
+  commitlint:
+    if: github.repository == 'bottlerocket-os/bottlerocket-kernel-kit'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Setup Node
+        uses: actions/setup-node@v4
+      - name: Install commitlint
+        run: npm install @commitlint/cli @commitlint/types
+      - name: Lint commits in PR
+        env:
+          WORKSPACE: ${{ github.workspace }}
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: |
+          npx commitlint \
+            -g "${WORKSPACE}/.commitlint.config.mjs" \
+            --from "${BASE_SHA}" \
+            --to "${HEAD_SHA}" \
+            --verbose