Leveraging Automated Unit Tests for Unsupervised Code Translation

Baptiste Roziere, Jie Zhang, Francois Charton, Mark Harman, Gabriel Synnaeve, Guillaume Lample

Keywords: unsupervised, translation, code, self-training, pseudo-labelling, unit tests, programming languages, deep learning, transformer

Abstract: With little to no parallel data available for programming languages, unsupervised methods are well-suited to source code translation. However, the majority of unsupervised machine translation approaches rely on back-translation, a method developed in the context of natural language translation and one that inherently involves training on noisy inputs. Unfortunately, source code is highly sensitive to small changes; a single token can result in compilation failures or erroneous programs, unlike natural languages where small inaccuracies may not change the meaning of a sentence. To address this issue, we propose to leverage an automated unit-testing system to filter out invalid translations, thereby creating a fully tested parallel corpus. We found that fine-tuning an unsupervised model with this filtered data set significantly reduces the noise in the translations so-generated, comfortably outperforming the state-of-the-art for all language pairs studied. In particular, for Java→Python and Python→C++ we outperform the best previous methods by more than 16% and 24% respectively, reducing the error rate by more than 35%.

One-sentence Summary: We leverage automatically created multilingual unit tests to improve unsupervised machine translation methods for source code and substantially outperform the state-of-the-art on all the language pairs we consider.