Filters Gmail message threads to apply helpful GitHub labels, for organization.

label-github-emails-in-gmail.gs

/**
 * Labels Gmail email threads
 */
function labelGithubEmails() {
  /**
   * Gmail label names for GitHub messages
   */
  const githubLabelName = 'GitHub'
  const githubPullRequestLabelName = 'GitHub/Pull Request'
  const githubIssueLabelName = 'GitHub/Issue'
  const githubDiscussionLabelName = 'GitHub/Discussion'
  const githubReleaseLabelName = 'GitHub/Release'
  const githubCommitLabelName = 'GitHub/Commit'
  
  const githubLabel = GmailApp.getUserLabelByName(githubLabelName)
  const githubPullRequestLabel = GmailApp.getUserLabelByName(githubPullRequestLabelName)
  const githubIssueLabel = GmailApp.getUserLabelByName(githubIssueLabelName)
  const githubDiscussionLabel = GmailApp.getUserLabelByName(githubDiscussionLabelName)
  const githubReleaseLabel = GmailApp.getUserLabelByName(githubReleaseLabelName)
  const githubCommitLabel = GmailApp.getUserLabelByName(githubCommitLabelName)
  
  /**
   * The query to use when finding messages to process
   *
   * Tweak this to improve the processing time/performance of messages, especially to prevent reaching maximum time/limits defined in the quotas.
   *
   * See: https://support.google.com/mail/answer/7190
   * See: https://developers.google.com/apps-script/guides/services/quotas#current_limitations
   */
  const gmailSearchQuery = '(label:github AND NOT label:github-pull-request AND NOT label:github-issue AND NOT label:github-discussion AND NOT label:github-release AND NOT label:github-commit) AND newer_than:1d';
  
  const rfc822MessageIdHeaderName = 'Message-ID'
  
  const pullRequestMessageIdRegex = /.*\/pull(s)?\/.*@github.com/i;
  const issueMessageIdRegex = /.*\/issue(s)?\/.*@github.com/i;
  const discussionMessageIdRegex = /.*\/discussion(s)?\/.*@github.com/i;
  const releaseMessageIdRegex = /.*\/release(s)?\/.*@github.com/i;
  const commitMessageIdRegex = /.*\/commit(s)?\/.*@github.com/i;
  
  const maxPerPage = 50;
  var startIndex = 0;
  
  do {
    var threads = GmailApp.search(gmailSearchQuery, startIndex, maxPerPage);
    
    Logger.log('Gmail search query found %s results, with a range of %s-%s', threads.length, startIndex, (startIndex + maxPerPage))
    
    threads.forEach(function (gmailThread) {
      var firstMessage = gmailThread.getMessages()[0];
      
      var mailRFCMessageIds = getEmailHeaderValues(firstMessage.getRawContent(), rfc822MessageIdHeaderName);
      
      // Determine the type of message
      var [isPullRequest, isIssue, isDiscussion, isRelease, isCommit] = mailRFCMessageIds.reduce(
        function ([isPullRequestMessage, isIssueMessage, isDiscussionMessage, isReleaseMessage, isCommitMessage], messageId) {
          // Test for message type
          isPullRequestMessage = isPullRequestMessage || pullRequestMessageIdRegex.test(messageId);
          isIssueMessage = isIssueMessage || issueMessageIdRegex.test(messageId);
          isDiscussionMessage = isDiscussionMessage || discussionMessageIdRegex.test(messageId);
          isReleaseMessage = isReleaseMessage || releaseMessageIdRegex.test(messageId);
          isCommitMessage = isCommitMessage || commitMessageIdRegex.test(messageId);
          
          return [isPullRequestMessage, isIssueMessage, isDiscussionMessage, isReleaseMessage, isCommitMessage];
        },
        [false, false, false, false, false]
      );
      
      Logger.log('Message (%s) with `Message-ID: %s` detected as %s', firstMessage.getId(), mailRFCMessageIds.join(', '), {"isPullRequest": isPullRequest, "isIssue": isIssue, "isDiscussion": isDiscussion, "isRelease": isRelease, "isCommit": isCommit})
      
      if (isPullRequest) {
        gmailThread.addLabel(githubPullRequestLabel);
      }
      
      if (isIssue) {
        gmailThread.addLabel(githubIssueLabel);
      }
      
      if (isDiscussion) {
        gmailThread.addLabel(githubDiscussionLabel);
      }
      
      if (isRelease) {
        gmailThread.addLabel(githubReleaseLabel);
      }
      
      if (isCommit) {
        gmailThread.addLabel(githubCommitLabel);
      }
    });
    
    startIndex += threads.length;
  } while (threads.length >= maxPerPage);
}


/**
 * Gets values for an email header
 */
function getEmailHeaderValues(rawEmail, headerName) {
  const headerRegex = new RegExp('^' + headerName + ': (.*(?:\\r?\\n\\s+.*)?)$', 'gim');
  
  var values = [];
  
  do {
    var matches = headerRegex.exec(rawEmail);
    
    if (Array.isArray(matches) && 1 in matches) {
      values.push(matches[1]);
    }
  } while (null !== matches);
  
  return values;
}

To use this filter

1. Create labels in Gmail that match the names of the labels used in the script. In this script, there's a "GitHub" label, and then there are 4 sub-labels (nested labels) under the "GitHub" label. When done, your label structure in Gmail should look like this:
   
2. Open Google Drive and create a new "Google Apps Script"
   
3. Paste the code in this gist in a file called main.gs in the Google Apps Script project.
   
4. Once pasted, save the project.
5. Under the Edit menu, choose "Current project's triggers".
   
6. Add a "Time-driven" trigger that run's the labelGithubEmails function every minute.
   

It should work now!