* @param {string[]} files - the gitStream's files context variable
 * @param {Object} pr - the gitStream's pr context variable
 * @param {string} token - access token with repo:read scope, used to read the CODEOWNERS file
 * @param {string} pathToCodeOwners - path from repo root to CODEOWNERS file
 * @returns {Map} - Map from owner name to list of files they own

*/
module.exports = async ({github, context}) => {
  const rollback_commit = context.payload.head_commit.id;
  const pr_match_groups = context.payload.head_commit.message.match(/\Rollback of PR #(\d+).*/) || [];
  if (pr_match_groups.length != 2) {
    console.log(`PR Number not found in ${context.payload.head_commit.message}`);
    throw "Error extracting PR Number from commit message";
  }

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