What is impactguard?

ImpactGuard is a tool for developers who want to understand the consequences of changing a function's interface before merging that change into a shared codebase. When you modify how a function works, for example, by removing a parameter or changing what a parameter means, other parts of the code that call that function may break silently. ImpactGuard automates the work of finding those at-risk call sites and scoring how dangerous the change is. It supports Python, TypeScript, JavaScript, Java, Kotlin, Go, Rust, Swift, C, C++, C#, Ruby, Haskell, and Zig. For each language, it parses the source code to extract function signatures (names, parameters, types), then compares them across two commits to classify what changed. Changes are labeled as breaking (such as removing a required argument) or non-breaking (such as adding an optional argument). It then scans the rest of the codebase for every place that calls the changed function using static call-site analysis, with optional runtime tracing to capture live execution patterns as well. The risk of each change is expressed as a score using a model the project calls S × E × C × λ, Severity, Exposure, Confidence, and Lambda, giving a single quantitative number that can be used as a gate in CI/CD pipelines to block merges that exceed a risk threshold. When breaking call sites are found, ImpactGuard can also generate format-preserving patches to fix them automatically using LibCST. The tool is installable from PyPI, requires Python 3.11 or higher, and includes a command-line interface. It is available under the topics ast, automatic-patching, call-graph, cicd-integration, commit-analysis, diff, git, and impact-analysis.