GitHub Actions CI fails: Cannot find 'main' branch for git diff (fatal: ambiguous argument 'main...HEAD')

[AbraaoAlves]

Problem

When running the codeguardian checks in a GitHub Actions CI environment, the job fails with the following error:

Error: fatal: ambiguous argument 'main...HEAD': unknown revision or path not in the working tree.

This breaks CI runs for projects that rely on GitHub-hosted runners and default checkout strategies.

Root Cause

• The CLI and npm scripts set main as the default base branch for git comparisons (e.g., --base main or -b main).
• In a typical GitHub Actions workflow, the local clone does not guarantee the presence of the main branch ref by default, especially if actions/checkout uses a shallow fetch (default fetch-depth: 1).
• As a result, any git diff main...HEAD or similar operation fails in CI, even though it works locally.

Evidence

• Full error: fatal: ambiguous argument 'main...HEAD': unknown revision or path not in the working tree.
• Scripts in package.json enforce -b main by default.

Suggested Solutions

• Make the CLI and workflow scripts resolve the actual default branch robustly, not just assume main exists.
• In CI, prefer to use origin/<default branch> or allow an override based on the GitHub event context (github.event.pull_request.base.ref).
• Add fallback logic in the CLI for when main isn't available as a local ref.
• Recommend in the README (and optionally in workflow examples) that users set fetch-depth: 0 in actions/checkout or otherwise ensure the base branch is locally present.