Out of step: Code clone detection for mobile apps across different language codebases

Clone detection provides insight about replicated fragments in a code base. With the rise of multi-language code bases, new techniques addressing cross-language code clone detection enable the analysis of polyglot systems. Such techniques have not yet been applied to the mobile apps' domain, which are naturally polyglot. Native mobile app developers must synchronize their code base in at least two different programming languages. App synchronization is a difficult and time-consuming maintenance task, as features can rapidly diverge between platforms, and feature identification must be performed manually. The end goal of this work is to provide an analysis framework to reduce the impact of app synchronization. A first step in this direction consists in a structural algorithm for cross-language clone detection, called Out of Step, exploiting the idea behind enriched concrete syntax trees. Such trees are used as a common intermediate representation built from programming languages' grammars, to detect similarities between app code bases. Our technique finds code similarities with over 80% for the evaluation of language features, where Type 1-3 clones are manually injected for the analysis of both single- and cross-language cases for Kotlin and Dart. We validate the feasibility and correctness of our approach through the evaluation of the main language constructs for Kotlin and Dart. To validate the effectiveness we use a first case study detecting clones between 12 sorting algorithms across Kotlin and Dart, identifying clone similarities with a precision between 67% and 95%. Finally, we use a corpus of 144 mobile apps implemented in Kotlin and Dart, correctly identifying code similarities for the full application logic.