ci: add addlicense linter to CI workflow for license checks

[Aswinr24]

Description:

This PR adds addlicense as a linter in the CI workflow to enforce copyright and license headers across the project. It ensures that all source files include the necessary license headers, and the CI will fail if any file is missing or incorrect.

Related Issues:

Closes #2558

Linked PRs:

This PR depends on the following fix in addlicense:

google/addlicense#172 (Fixes copyright holder check, ignores empty files, and adds support for spec files)

The current implementation remains unaffected since specific files are manually excluded. However, once a new version of addlicense incorporating the changes from the referenced PR is released, explicitly defining exclusions (such as empty init.py files) may no longer be necessary.

Changes Made:

• Added addlicense to CI workflow
• Configured it to check and enforce license headers
• Ensured the workflow fails if missing headers are detected

Checklist

• No CHANGELOG update needed

• No new tests needed

• No documentation update needed

[gemini-code-assist]

Hello @Aswinr24, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

Summary of Changes

This pull request introduces a new CI check using addlicense to ensure all source files have the correct license headers. It downloads the addlicense tool, configures it to check for the 'Google LLC' copyright holder, and fails the CI if any files are missing or have incorrect headers. The PR also depends on a fix in the upstream addlicense repository.

Highlights

• License Header Enforcement: Adds a CI check to enforce consistent license headers across the project using the addlicense tool.
• CI Workflow Integration: Integrates addlicense into the existing CI workflow to automatically verify license headers on each pull request.
• Dependency on Upstream Fix: Highlights the dependency on a specific pull request in the addlicense repository that fixes copyright holder checks and adds support for spec files.

Changelog

• .github/workflows/tests.yml
  • Adds a new job to the CI workflow to download, install, and run addlicense.
  • Configures addlicense to check for the 'Google LLC' copyright holder.
  • Fails the CI if any files are missing license headers or have incorrect ones.
  • Adds steps to download and extract the addlicense binary from GitHub releases.
  • Adds a check to verify if git status --porcelain returns any changes after running addlicense, indicating missing or incorrect headers.

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---

A license header, small and neat,
Ensures our code is bittersweet.
With copyright clear,
There's naught to fear,
And contributions we can greet.

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[gemini-code-assist]

Code Review

This PR introduces a license header check to the CI workflow, which is a valuable addition for maintaining code quality and compliance. The implementation is straightforward, but there are a few areas where it can be improved for robustness and user experience.

Summary of Findings

• Error Handling in CI Workflow: The CI workflow includes a check for license headers, but the error message could be improved to provide more specific guidance to the user. Suggesting a direct command to fix the issue would be beneficial.
• Downloading addlicense Binary: The CI workflow downloads the addlicense binary using curl and grep. This approach is fragile and depends on the structure of the GitHub API response. A more robust method, such as using the GitHub CLI or a dedicated action, would be preferable.

Merge Readiness

The PR is almost ready for merging. Addressing the error handling and binary download method would significantly improve the reliability and user-friendliness of the CI workflow. I am unable to directly approve the pull request, and other reviewers should also review and approve this code before merging. I recommend that the pull request not be merged until the high severity issues are addressed.