feat: add support for Co-authored-by commit trailers

[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
• 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 extracts co-author identifiers:

• GitHub noreply emails (e.g., username@users.noreply.github.com) - extracts the username
• Other email addresses (e.g., john@example.com) - uses the full email address as the identifier

Example commit message:

Feature implementation

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

Co-authors are added as contributors with contribution counts reflecting the number of commits they co-authored. 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

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[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 why set this to false if the configuration file has true by default. Maybe it's better not to have a default here?

[Copilot]

Removed default values from both get_contributors() and get_all_contributors() function parameters in commit 4454fe7. The acknowledge_coauthors parameter is now always explicitly passed from the configuration, eliminating the inconsistency.

[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