# LoweredCodeUtils.jl

This package performs operations on Julia's lowered AST. An introduction to this representation can be found at JuliaInterpreter.

Lowered AST (like other ASTs, type-inferred AST and SSA IR form) is generally more amenable to analysis than "surface" Julia expressions. However, sophisticated analyses can nevertheless require a fair bit of infrastructure. The purpose of this package is to standardize a few operations that are important in some applications.

Currently there are two major domains of this package: the "signatures" domain and the "edges" domain.

## Signatures

A major role of this package is to support extraction of method signatures, in particular to provide strong support for relating keyword-method "bodies" to their parent methods. The central challenge this addresses is the lowering of keyword-argument functions and the fact that the "gensymmed" names are different each time you lower the code, and therefore you don't recover the actual (running) keyword-body method. The technical details are described in this Julia issue and on the next page. This package provides a workaround to rename gensymmed variables in newly-lowered code to match the name of the running keyword-body method, and provides a convenience function, bodymethod, to obtain that otherwise difficult-to-discover method.

## Edges

Sometimes you want to run only a selected subset of code. For instance, Revise tracks methods by their signatures, and therefore needs to compute signatures from the lowered representation of code. Doing this robustly (including for @evaled methods, etc.) requires running module top-level code through the interpreter. For reasons of performance and safety, it is important to minimize the amount of code that gets executed when extracting the signature.

This package provides a general framework for computing dependencies in code, through the CodeEdges constructor. It allows you to determine the lines on which any given statement depends, the lines which "consume" the result of the current line, and any "named" dependencies (Symbol and GlobalRef dependencies). In particular, this resolves the line-dependencies of all SlotNumber variables so that their own dependencies will be handled via the code-line dependencies.