> Codemod is a tool/library to assist you with large-scale codebase refactors

Codemods are awesome, but I felt they were far from their potential, and so I’m very proud to show you all an early version of a codemod library we’ve built called Codemodder (https://codemodder.io) that we think moves the "field" forward. Codemodder supports both Python and Java (https://github.com/pixee/codemodder-python and https://github.com/pixee/codemodder-java). The license is AGPL, please don’t kill me.

Primarily, what makes Codemodder different is our design philosophy. Instead of trying to write a new library for both finding code and changing code, which is what traditional codemod libraries do, we aim to provide an easy-to-use orchestration library that helps connect idiomatic tools for querying source code and idiomatic tools for mutating source code.

So, if you love your current linter, Semgrep, Sonar, or PMD, CodeQL or whatever for querying source code – use them! If you love JavaParser or libCST for changing source code – use them! We’ll provide you with all the glue and make building, testing, packaging and orchestrating them easy.

Here are the problems with existing codemod libraries as they exist today, and how Codemodder solves them.

1. They’re not expressive enough. They tend to offer barebones APIs for querying code. There’s simply no way for these libraries to compete with purpose-built static analysis tools for querying code, so we should use them instead.

2. They produce changes without any context. Understanding why a code change is made is important. If the change was obvious to the developer receiving the code change, they probably wouldn’t have made the mistake in the first place! Storytelling is everything, and so we guide you towards making changes that are more likely to be merged.

3. They don’t handle injecting dependencies well. I have to say we’re not great at this yet either, but we have some of the basics and will invest more.

4. Most apps involve multiple languages, but all of today’s codemod libraries are for one language, so they are hard to orchestrate for a single project. We’ve put a lot of work into making sure these libraries are aligned with open source API contracts and formats (https://github.com/pixee/codemodder-specs) so they can be orchestrated similarly by downstream automation.

The idea is "don’t write another PR comment saying the same thing, write a codemod to just make the change automatically for you every time". We hope you like it, and are excited to get any feedback you might have!