auto-format-apply.yml

name: Auto Format — Apply

# Stage 2 of 2. Runs after "Auto Format" completes on a PR. This job has
# elevated permissions to push the formatted patch back to the PR branch,
# but it never executes code from the PR — it only downloads the inert
# patch artifact, checks out the measured head SHA, and applies the diff.
on:
  workflow_run:
    workflows: ["Auto Format"]
    types: [completed]

permissions:
  # actions:read is needed for listWorkflowRunArtifacts / downloadArtifact.
  # pull-requests:read is needed for pulls.get in the Resolve PR step.
  # contents:read is a safety default; the push-back steps use the app token.
  actions: read
  contents: read
  pull-requests: read

jobs:
  apply:
    name: Apply
    if: github.event.workflow_run.conclusion == 'success'
    runs-on: ubuntu-latest
    timeout-minutes: 10
    steps:
      - name: Download patch artifact
        id: download
        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
        with:
          script: |
            const fs = require('node:fs');
            const path = require('node:path');
            const { data } = await github.rest.actions.listWorkflowRunArtifacts({
              owner: context.repo.owner,
              repo: context.repo.repo,
              run_id: context.payload.workflow_run.id,
            });
            const artifact = data.artifacts.find((a) => a.name === 'auto-format-patch');
            if (!artifact) {
              core.setOutput('found', 'false');
              core.info('No patch artifact — nothing to apply.');
              return;
            }
            const download = await github.rest.actions.downloadArtifact({
              owner: context.repo.owner,
              repo: context.repo.repo,
              artifact_id: artifact.id,
              archive_format: 'zip',
            });
            // Stage the artifact under RUNNER_TEMP, not GITHUB_WORKSPACE.
            // GITHUB_WORKSPACE is wiped by the later actions/checkout step
            // (clean: true is the default), which would delete the payload
            // before the Apply step can reach it. RUNNER_TEMP sits outside
            // the workspace and survives checkout.
            const outDir = path.join(process.env.RUNNER_TEMP, 'af-artifact');
            fs.mkdirSync(outDir, { recursive: true });
            fs.writeFileSync(path.join(outDir, 'artifact.zip'), Buffer.from(download.data));
            core.setOutput('found', 'true');

      - name: Unpack artifact
        if: steps.download.outputs.found == 'true'
        run: |
          cd "$RUNNER_TEMP/af-artifact"
          unzip -o artifact.zip
          ls -la

      - name: Resolve PR
        if: steps.download.outputs.found == 'true'
        id: pr
        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
        with:
          script: |
            const fs = require('node:fs');
            const path = require('node:path');
            const prNumber = Number(
              fs.readFileSync(
                path.join(process.env.RUNNER_TEMP, 'af-artifact', 'pr-number'),
                'utf8',
              ).trim(),
            );
            if (!Number.isInteger(prNumber) || prNumber <= 0) {
              core.setFailed(`Invalid PR number in artifact: ${prNumber}`);
              return;
            }
            // Cross-check: fetch the PR and verify its head SHA matches the
            // workflow_run's head SHA, so a forged artifact can't redirect
            // the push at an unrelated branch.
            const headSha = context.payload.workflow_run.head_sha;
            let pr;
            try {
              const { data } = await github.rest.pulls.get({
                owner: context.repo.owner,
                repo: context.repo.repo,
                pull_number: prNumber,
              });
              pr = data;
            } catch (err) {
              core.setFailed(`Failed to fetch PR #${prNumber}: ${err.message}`);
              return;
            }
            if (pr.head.sha !== headSha) {
              core.setFailed(
                `PR #${prNumber} head SHA (${pr.head.sha}) does not match workflow_run head SHA (${headSha}). The branch has moved on; the next PR event will re-run format+apply.`,
              );
              return;
            }
            core.setOutput('number', String(pr.number));
            core.setOutput('ref', pr.head.ref);
            // Push onto the exact commit that was formatted. If the branch
            // has advanced since, the push fails non-fast-forward rather than
            // applying a stale patch to a newer tree.
            core.setOutput('sha', headSha);
            core.setOutput('full_name', pr.head.repo.full_name);
            const isFork = pr.head.repo.fork
              || pr.head.repo.full_name !== `${context.repo.owner}/${context.repo.repo}`;
            core.setOutput('is_fork', isFork.toString());

      - name: Generate app token
        if: steps.download.outputs.found == 'true'
        id: app-token
        uses: actions/create-github-app-token@bcd2ba49218906704ab6c1aa796996da409d3eb1 # v3.2.0
        with:
          client-id: ${{ secrets.APP_ID }}
          private-key: ${{ secrets.APP_PRIVATE_KEY }}
          # Push the formatted commit (contents) and comment on push failure
          # (pull-requests). Nothing else.
          permission-contents: write
          permission-pull-requests: write

      # --- Same-repo PRs: checkout the measured SHA and push directly ---

      - name: Checkout (same-repo)
        if: steps.download.outputs.found == 'true' && steps.pr.outputs.is_fork == 'false'
        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          ref: ${{ steps.pr.outputs.sha }}
          token: ${{ steps.app-token.outputs.token }}
          # The same-repo push step below pushes the formatted commit back to
          # the PR branch using this credential.
          persist-credentials: true

      # --- Fork PRs: checkout the fork at the measured SHA so we can push back ---

      - name: Checkout (fork)
        if: steps.download.outputs.found == 'true' && steps.pr.outputs.is_fork == 'true'
        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          repository: ${{ steps.pr.outputs.full_name }}
          ref: ${{ steps.pr.outputs.sha }}
          persist-credentials: false
          # Reviewed opt-in to checkout v7's fork guard: no code from the
          # fork tree is ever executed here. The steps below only `git apply`
          # the patch from the trusted format artifact and run git
          # add/commit/push — no scripts, hooks, or tooling from the
          # checked-out tree. Credentials are not persisted; the push uses
          # a scoped app token via GIT_ASKPASS.
          allow-unsafe-pr-checkout: true

      - name: Apply patch
        if: steps.download.outputs.found == 'true'
        id: apply
        run: |
          git apply "$RUNNER_TEMP/af-artifact/format.patch"
          git add -A
          if git diff --staged --quiet; then
            echo "no_diff=true" >> "$GITHUB_OUTPUT"
            echo "Patch is a no-op against the checked-out head — nothing to push."
          else
            echo "no_diff=false" >> "$GITHUB_OUTPUT"
          fi

      - name: Commit and push (same-repo)
        if: |
          steps.download.outputs.found == 'true'
          && steps.pr.outputs.is_fork == 'false'
          && steps.apply.outputs.no_diff == 'false'
        env:
          HEAD_REF: ${{ steps.pr.outputs.ref }}
          HEAD_SHA: ${{ steps.pr.outputs.sha }}
        run: |
          set -e
          git config user.name "emdashbot[bot]"
          git config user.email "emdashbot[bot]@users.noreply.github.com"
          git commit -m "style: format"
          # Detached-HEAD push onto the PR branch. If the branch has advanced
          # past the measured SHA, this fails non-fast-forward — the next PR
          # event re-runs format+apply against the new head.
          if ! git push origin "HEAD:$HEAD_REF"; then
            echo "::error::Non-fast-forward push — the PR branch moved past the measured SHA $HEAD_SHA. The next PR event will re-run format+apply." >&2
            exit 1
          fi

      - name: Commit and push (fork)
        if: |
          steps.download.outputs.found == 'true'
          && steps.pr.outputs.is_fork == 'true'
          && steps.apply.outputs.no_diff == 'false'
        id: push-fork
        env:
          APP_TOKEN: ${{ steps.app-token.outputs.token }}
          HEAD_REF: ${{ steps.pr.outputs.ref }}
          FULL_NAME: ${{ steps.pr.outputs.full_name }}
        run: |
          git config user.name "emdashbot[bot]"
          git config user.email "emdashbot[bot]@users.noreply.github.com"
          git commit -m "style: format"
          # Push the formatted commit to the fork via the app token, supplied
          # through GIT_ASKPASS so it never lands in process args or git config.
          export GIT_ASKPASS="$RUNNER_TEMP/git-askpass.sh"
          printf '#!/bin/sh\necho "%s"\n' "$APP_TOKEN" > "$GIT_ASKPASS"
          chmod +x "$GIT_ASKPASS"
          git remote add fork "https://x-access-token@github.com/$FULL_NAME.git"
          if git push fork "HEAD:$HEAD_REF"; then
            echo "push_failed=false" >> "$GITHUB_OUTPUT"
          else
            echo "push_failed=true" >> "$GITHUB_OUTPUT"
          fi
          rm -f "$GIT_ASKPASS"

      - name: Comment on push failure
        if: steps.push-fork.outputs.push_failed == 'true'
        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
        env:
          PR_NUMBER: ${{ steps.pr.outputs.number }}
        with:
          github-token: ${{ steps.app-token.outputs.token }}
          script: |
            await github.rest.issues.createComment({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: Number(process.env.PR_NUMBER),
              body: `Could not push formatting changes to this fork. The contributor may have "Allow edits by maintainers" disabled.\n\nPlease run the formatter locally:\n\n\`\`\`\npnpm format\n\`\`\``,
            });