Learning migration models for supporting incremental language migrations of software applications

Context: A Legacy system can be defined as a system that significantly resists modification and evolution. According to the literature, there are two main strategies to migrate a legacy system: (a) to replace the legacy system by a new one, (b) to incrementally migrate parts from the legacy system to the new one. Incremental migration allows developers to better control the risks that may occur during the migration process. However, this strategy is more complex because it requires decomposition of the legacy system into different parts, e.g. a set of files, and to define the order of migration of them along the migration process. To our knowledge, there is no approach to support developers on those activities. Objective: This paper presents an approach, named MigrationExp, to support incremental language migrations of applications from one source language to another target language. MigrationExp recommends the files that should be migrated first in a particular migration iteration. As a novelty, our approach relies on a ranking model learned, using a learning-to-rank algorithm, from migrations made by developers. Method: We validate our approach in the context of the migrations of Android apps, from Java to Kotlin, a new official language for Android. We train our model using migrations of Java code to Kotlin written by developers on open-source applications. Results: The results show that, on the task of proposing files to migrate, our approach outperforms a previous migration strategy proposed by Google, in terms of its ability to accurately predict empirically observed migration orders. Conclusion: Since most Android applications are written in Java, we conclude that approaches to support developers such as MigrationExp may significantly impact the development of Android applications.