Function postOrUpdatePrComment

packages/bumpy/src/commands/ci.ts:1717–1763

(
  prNumber: string,
  body: string,
  rootDir: string,
  marker: string = COMMENT_MARKER,
)

const SNAPSHOT_COMMENT_MARKER = '<!-- bumpy-snapshot -->';

async function postOrUpdatePrComment(
  prNumber: string,
  body: string,
  rootDir: string,
  marker: string = COMMENT_MARKER,
): Promise<void> {
  const validPr = validatePrNumber(prNumber);
  const markedBody = `${marker}\n${body}`;

  try {
    // Find existing bumpy comment using gh with jq. The marker keeps each kind of comment
    // (release plan vs snapshot) independent, so they don't overwrite each other.
    const jqFilter = `.comments[] | select(.body | startswith("${marker}")) | .url | capture("issuecomment-(?<id>[0-9]+)$") | .id`;
    const existingComment = tryRunArgs(['gh', 'pr', 'view', validPr, '--json', 'comments', '--jq', jqFilter], {
      cwd: rootDir,
    });

    // Take the first result if multiple
    const commentId = existingComment?.split('\n')[0]?.trim();

    if (commentId) {
      await runArgsAsync(
        ['gh', 'api', `repos/{owner}/{repo}/issues/comments/${commentId}`, '-X', 'PATCH', '-F', 'body=@-'],
        { cwd: rootDir, input: markedBody },
      );
      log.dim('  Updated PR comment');
    } else {
      await runArgsAsync(['gh', 'pr', 'comment', validPr, '--body-file', '-'], {
        cwd: rootDir,
        input: markedBody,
      });
      log.dim('  Posted PR comment');
    }
  } catch (err) {
    log.warn(`  Failed to comment on PR: ${err instanceof Error ? err.message : err}`);
    // Most common cause: the workflow is on `pull_request` and this is a fork PR,
    // so GITHUB_TOKEN is read-only. Surface that explicitly — otherwise contributors
    // see a red check with no comment and no clue why.
    if (process.env.GITHUB_EVENT_NAME === 'pull_request' && isForkPr()) {
      log.warn(
        '  This PR is from a fork. Fork PRs running on `pull_request` get a read-only token\n' +
          '  and cannot post comments. Switch the workflow to `pull_request_target` —\n' +
          '  see https://bumpy.varlock.dev/docs/github-actions',
      );
    }
  }
}

function detectPrBranch(rootDir: string): string | null {
  // GitHub Actions sets GITHUB_HEAD_REF for pull_request events