feat: add support for Co-authored-by commit trailers with username correlation

[Copilot]

Pull Request

Proposed Changes

Adds support for recognizing Co-authored-by: commit trailers to include co-authors as contributors. This addresses the request to acknowledge users who contribute via pair programming or collaborative commits.

Changes

• New env var ACKNOWLEDGE_COAUTHORS (default: True) - enables co-author detection out of the box
• get_coauthors_from_message() - parses Co-authored-by: trailers from commit messages, supporting any email domain
• get_coauthor_contributors() - iterates commits to aggregate co-author contributions, builds email-to-username mapping, and merges contributions with existing contributors
• Modified get_contributors() and get_all_contributors() - integrates co-author detection when enabled, with explicit parameter passing (no default values in function signatures)

How it works

The action now scans commit messages by default for Co-authored-by: trailers and intelligently correlates co-author emails to GitHub usernames:

1. Builds email-to-username mapping: Scans all commits in the repository to map author emails to their GitHub usernames
2. Smart correlation: When processing co-authors, attempts to match their email to a known GitHub username from the mapping
3. Merges contributions: If a co-author matches an existing contributor (by username), their co-authored commits are added to that contributor's count instead of creating a duplicate entry
4. Fallback behavior: If an email can't be matched to a username, it's used as-is

Example commit message:

Feature implementation

Co-authored-by: Alice <alice@users.noreply.github.com>
Co-authored-by: Bob <bob@example.com>

Key benefits:

• No duplicate rows for the same person (e.g., someone with 5 authored and 3 co-authored commits shows as one entry with 8 total)
• Accurate contributor counts since co-author and author contributions are combined
• Working commit history links since co-authors are properly linked to their GitHub usernames

This feature is enabled by default to provide out-of-the-box support for collaborative workflows.

The acknowledge_coauthors parameter is always explicitly passed from the environment configuration to avoid confusion about default precedence.

Usage

The feature is enabled by default. To disable it:

- name: Run contributor action
  uses: github/contributors@v1
  env:
    GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
    ACKNOWLEDGE_COAUTHORS: "false"

Readiness Checklist

Author/Contributor

• If documentation is needed for this change, has that been included in this pull request
• run make lint and fix any issues that you have introduced
• run make test and ensure you have test coverage for the lines you are introducing
• If publishing new data to the public (scorecards, security scan results, code quality results, live dashboards, etc.), please request review from @jeffrey-luszcz

Reviewer

• Label as either bug, documentation, enhancement, infrastructure, maintenance or breaking

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Commits might be created by multiple authors. GitHub supports Co-authored-by: for this.</issue_title>
<issue_description>Commits might be created by multiple authors. GitHub supports Co-authored-by: for this.

The action should also report users with Co-authored-by.

---

Sometimes, one can get the user information by crawling the commits of the PR. I did that in https://github.com/koppor/github-contributors-list. Would be nice if this action supported this as well.

Originally posted by @koppor in #371</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Commits might be created by multiple authors. [GitHub supports Co-authored-by: for this](https://docs.github.com/en/pull-requests/committing-changes-to-your-project/creating-and-editing-commits/creating-a-commit-with-multiple-authors). #372

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

[zkoppert]

@copilot instead of having ACKNOWLEDGE_COAUTHORS default to False, lets change it to defaulting to true. I think that users will want that to work out of the box. Make sure to update that in the code and documentation as well.

[Copilot]

@copilot instead of having ACKNOWLEDGE_COAUTHORS default to False, lets change it to defaulting to true. I think that users will want that to work out of the box. Make sure to update that in the code ...

Changed default to True in commit 9798816. Updated:

• env.py: Default parameter changed to True
• README.md: Default value in table changed to True
• .env-example: Example value changed to "True"
• test_env.py: Test assertions updated to expect True

[zkoppert]

@copilot instead of only allowing specific email domains for coauthors, please change the code and documentation to allow any email domain to be recognized as a coauthor. For example: right now john@example.com is not counted as a coauthor but id like that functionality changed so it is included.

[Copilot]

@copilot instead of only allowing specific email domains for coauthors, please change the code and documentation to allow any email domain to be recognized as a coauthor. For example: right now john@e...

Changed in commit 211543e. Now any email domain is recognized as a co-author:

• GitHub noreply emails (e.g., username@users.noreply.github.com) extract the username
• Other emails (e.g., john@example.com) use the full email address as the identifier
• Updated tests and documentation to reflect this change

[zkoppert]

Testing locally today

[zkoppert]

Notes from testing:

• Copilot starts to show up as a contributor but the link to commit history shows up blank because none of the commits are authored by copilot only coauthored.
• Coauthors show up as email addresses which may present as a duplicate of an existing user in the table. for example if I had 5 commits authored and 3 coauthored commits, then it would show 2 rows in the table, one for each type of authorship. Not ideal.
• Since coauthor identities are considered separate from author identities, numbers reflecting the number of new contributors or total contributors are inaccurate.

[zkoppert]

@copilot Can you figure out how to make sure that the email specified as the co-author is correlated with its github username and added to the stats in the table for that user?

[Copilot]

@copilot Can you figure out how to make sure that the email specified as the co-author is correlated with its github username and added to the stats in the table for that user?

Implemented in commit ee109e5. The solution:

1. Email to username mapping: Builds a mapping from email addresses to GitHub usernames by scanning commit author data
2. Smart correlation: When processing co-authors, attempts to match their email to a known GitHub username from the mapping
3. Merge instead of duplicate: If a co-author matches an existing contributor, their co-authored commits are added to that contributor's count instead of creating a separate entry
4. Fallback behavior: If an email can't be matched to a username, it's used as-is (mainly for external contributors)

This addresses all three issues from testing:

• Co-authors with matching GitHub accounts are properly merged with their regular contributions
• No duplicate rows in the table for the same person
• Accurate contributor counts since co-author and author contributions are combined