Mapping Modern JVM Language Code to Analysis-friendly Graphs: A Pilot Study with Kotlin

Abstract

Kotlin is a modern JVM language, gaining adoption rapidly and becoming Android official programming language. With its widely usage, the need for code analysis of Kotlin is increasing. Exposing code semantics explicitly with a properly structured format is the first step in code analysis and the construction of such representation is the foundation for downstream tasks. Recently, graph-based approaches become a promising way for encoding source code semantics. However, current works mainly focus on representation learning with limited interpretability and shallow domain knowledge. The known evolvements of code semantics in new-generation programming languages have been overlooked. How to establish an effective mapping between naturally concise Kotlin source code with graph-based representation needs to be studied by analyzing known language features. In this paper, we propose a first-sight, rule-based mapping method, using composite representation with AST, CFG, DFG, and language features. We evaluate mapping strategies with ablation experiments by simulating a code search solution as a downstream task. Our graph-based method with built-in language features outperforms the text-based way without introducing greater complexity. By addressing the practical barriers to extracting and exposing the hidden semantics from Kotlin source code, our study also helps enlighten source code representations for other modern languages.