Signature Equality Is Not Behavioural Equality: Building a Dependency Migrator With Zero Dependencies

The author explores the complexities of migrating Go project dependencies to the standard library, highlighting that signature equality does not guarantee behavioural equivalence. While Go's standard library has evolved to include functionality previously provided by third-party packages, mechanical replacement can introduce subtle bugs. The author details the development of 'molt', a static-analysis tool built entirely with the Go standard library to safely automate these migrations. By avoiding third-party dependencies, the tool adheres to strict hackathon constraints while ensuring code safety through rigorous AST analysis and version-gate checks. The project emphasizes that automation should stop where confidence ends, leading to a design that prioritizes correctness over aggressive refactoring. The article serves as a technical case study on the risks of automated code migration and the importance of deep static analysis when replacing external dependencies with native language features.