ci: Extract the pre-commit step in a dedicated workflow that would comment on the PR what the user should do next

Ideally, we could automatically push changes to the PR branch, but this would require elevated permissions (like running in a pull_request_target trigger), which come with certain restrictions (like the fact that the PR checks will not be re-triggered on a push by the GH Actions bot)

Signed-off-by: Armel Soro <[email protected]>

Author: rm3l

.github/workflows/pre-commit.yaml

@@ -0,0 +1,75 @@
+name: Pre-commit
+
+on:
+  pull_request:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.number }}
+  cancel-in-progress: true
+
+jobs:
+  pre-commit:
+    name: Pre-commit
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write  # Required to post comments
+    env:
+      GO111MODULE: on
+    steps:
+      - name: Checkout
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # pin@v3
+        with:
+          fetch-depth: 0
+
+      - uses: actions/setup-python@e797f83bcb11b83ae66e0230d6156d7c80228e7c # pin@v4
+        with:
+          python-version: 3.12
+
+      - uses: actions/setup-go@44694675825211faa026b3c33043df3e48a5fa00 # pin@v3
+        with:
+          go-version: ^1
+
+      - name: Setup helm-docs
+        run: go install github.com/norwoodj/helm-docs/cmd/helm-docs@latest
+
+      - name: Run pre-commit
+        uses: pre-commit/action@2c7b3805fd2a0fd8c1884dcaebf91fc102a13ecd # [email protected]
+        continue-on-error: true  # Don't fail immediately; we'll handle it below
+        with:
+          extra_args: --verbose --all-files --show-diff-on-failure
+
+      - name: Check for changes after pre-commit
+        id: diff-checker
+        run: |
+          echo "CHANGED=$(if git diff --quiet; then echo "false"; else echo "true"; fi)" >> $GITHUB_OUTPUT
+
+      - name: Comment PR with diff
+        if: ${{ steps.diff-checker.outputs.CHANGED == 'true' }}
+        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8
+        with:
+          script: |
+            const {
+              exitCode,
+              stdout,
+              stderr
+            } = await exec.getExecOutput('git', ['diff']);
+            console.log(exitCode, stderr);
+
+            const body = `
+              ## Pre-commit Hook Failures
+              <details>
+              <summary>View diff</summary>
+
+              \`\`\`diff
+              ${stdout}
+              \`\`\`
+
+              </details>
+              Please apply the above diff in your PR branch (or run `pre-commit run --all-files` locally) and push the changes.
+            `;
+            github.rest.issues.createComment({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: body
+            });