Lossless Semantic Tree (LST)

What is it?

An LST is OpenRewrite’s internal representation of source code. Unlike a regular Abstract Syntax Tree (AST), it preserves every formatting detail — whitespace, comments, import order — while also carrying full type information. This means a recipe can modify code and produce a diff that looks like a human wrote it.

Why does it matter?

Without an LST, automated code transformations are either lossy (they destroy formatting) or blind (they lack type context). The LST is what makes OpenRewrite transformations predictable and reviewable. It’s the difference between a find-and-replace and a compiler-aware refactoring.