2 posts tagged with "coverage"

Dify is a large open-source platform for building LLM applications. Its backend is a Python Flask application with workflows, RAG pipelines, model providers, agents, Celery tasks, database migrations, and a large test suite. That makes it a useful case study for Pyrefly adoption: a real codebase where static analysis needs to fit into existing CI without blocking daily work.

The goal was not to make every Pyrefly diagnostic fail CI on day one. That would have been noisy and counterproductive. The better approach was to split the rollout into two CI surfaces: a blocking check for the files we were ready to enforce, and full-project reporting that stayed non-blocking and showed up in PR comments.

At Pyrefly, we've always believed that type coverage is one of the most important indicators of code quality. Over the past year, we've worked closely with teams across large Python codebases here at Meta - improving performance, tightening soundness, and making type checking a seamless part of everyday development.

But one question kept coming up: What would it take to reach 100% type coverage?

Today, we're excited to share a breakthrough.