downstream-breakage-radar 0.2.1

A GitHub Action and CLI that detects breaking changes before release and generates plain English migration notes

📡 Downstream Breakage Radar

Detect breaking changes before they break your users.

A GitHub Action and CLI that scans your pull requests for changes likely to break downstream consumers — and generates plain-English migration notes so nobody gets surprised on release day.

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Why?

Every library maintainer has lived this nightmare: you merge a PR, cut a release, and within hours your issue tracker fills up with reports from projects that depended on the function you renamed, the config key you removed, or the default you changed.

Downstream Breakage Radar catches those risks before they reach main. It diffs your branch against a base ref, identifies changes that touch public API surfaces and release-critical files, and tells you — in plain English — what downstream users will need to do.

No external dependencies. No complex setup. Just add it to your workflow and ship with confidence.

✨ Features

• 🔍 Automatic surface detection — flags changes to src/, lib/, api/, schemas/, proto/, OpenAPI specs, and more
• 📦 Package manifest awareness — catches edits to pyproject.toml, package.json, Cargo.toml, go.mod, pom.xml, etc.
• 📝 Migration notes — every finding includes a human-readable note explaining what to review
• 🎯 Risk scoring — summarizes overall risk level (none / low / medium) at a glance
• 🖥️ Dual mode — runs as a GitHub Action in CI or locally as a CLI
• 📊 Multiple output formats — plain text for humans, JSON for tooling
• 🪶 Zero dependencies — pure Python, nothing to install beyond the standard library

🚀 Quick Start

As a GitHub Action (recommended)

Add this to .github/workflows/breakage-radar.yml:

name: Breakage Radar

on:
  pull_request:

jobs:
  scan:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Scan for breaking changes
        uses: Tahiram32/downstream-breakage-radar@main
        with:
          base-ref: origin/main
          format: markdown
          fail-on: high

As a CLI

# Install from source
pip install git+https://github.com/Tahiram32/downstream-breakage-radar.git

# Scan the current repo against origin/main
breakage-radar --repo . --base origin/main

# Get JSON output for CI tooling
breakage-radar --repo . --base origin/main --format json

Or run directly as a module:

python -m downstream_breakage_radar.cli --repo . --base origin/main

📋 Example Output

Text format

Risk level: medium
Changed files: 4
Findings: 3

- [medium] src/api/client.py: Change touches a likely public surface or release-critical file.
  Migration note: Review for API compatibility, config drift, and release notes before merging.

- [low] src/api/client.py: Source code change may affect downstream consumers.
  Migration note: Check for renamed symbols, changed defaults, and behavior shifts.

- [medium] pyproject.toml: Change touches a likely public surface or release-critical file.
  Migration note: Review for API compatibility, config drift, and release notes before merging.

JSON format

{
  "change_count": 4,
  "changed_files": [
    "src/api/client.py",
    "pyproject.toml",
    "docs/guide.md",
    "tests/test_client.py"
  ],
  "finding_count": 3,
  "findings": [
    {
      "message": "Change touches a likely public surface or release-critical file.",
      "migration_note": "Review for API compatibility, config drift, and release notes before merging.",
      "path": "src/api/client.py",
      "severity": "medium"
    }
  ],
  "risk_level": "medium"
}

⚙️ Configuration

Input	Default	Description
--repo	.	Path to the Git repository to scan
--base	origin/main	Base ref to diff against (branch, tag, or commit SHA)
--format	text	Output format: text for human-readable, json for machine-readable
--fail-on	high	The risk level at which to exit with code 1
--draft-release	false	Automatically draft a GitHub release using the gh CLI

Ignore Files

Create a .breakageignore file in the root of your repository to specify glob patterns for paths you want the scanner to completely ignore (e.g. src/internal_scripts/* or *_test.py).

GitHub Action inputs

When using as a GitHub Action, pass configuration via the with keyword. The action requires fetch-depth: 0 on checkout so the full git history is available for diffing.

🔬 How It Works

1. Diff — runs git diff --name-only <base-ref>...HEAD to get the list of changed files
2. Classify — checks each path against known risky patterns:
   • Path markers: src/, lib/, app/, api/, public/, include/, internal/, pkg/, schemas/, proto/, openapi
   • Package manifests: pyproject.toml, package.json, Cargo.toml, go.mod, pom.xml, build.gradle, and more
   • Source extensions: .py, .ts, .js, .go, .rs, .java, .kt, .cs
3. Score — assigns severity (low for source changes, medium for public surface / manifest changes)
4. Report — generates a summary with per-file findings and plain-English migration notes

🗺️ Roadmap

• Diff-aware API surface detection (AST-level analysis)
• Language-specific adapters for smarter risk scoring (Python added)
• Automated release-note drafting
• Downstream repository impact hints
• fail-on threshold to block PRs above a risk level
• Native GitHub inline annotations (Workflow Commands)

🤝 Contributing

Contributions are welcome! Please read CONTRIBUTING.md for guidelines on setting up the dev environment, running tests, and submitting pull requests.

This project follows the Contributor Covenant Code of Conduct.

📄 License

This project is licensed under the MIT License — see the LICENSE file for details.

❤️ Sponsor This Project

Downstream Breakage Radar is free, open-source software maintained in spare time. Sponsorship directly funds:

• 🛠️ New features from the roadmap (AST analysis, language adapters, SARIF output)
• 🐛 Bug fixes and maintenance to keep the tool reliable
• 📖 Documentation and examples to help more teams adopt it
• 🌍 Community support — answering issues, reviewing PRs, and growing the ecosystem

If this tool saves your team from a breaking release, consider supporting its development:

→ Sponsor @Tahiram32 on GitHub

Every contribution — no matter the size — helps keep this project alive and moving forward. Thank you! 🙏