Gamma: Revisiting Template-Based Automated Program Repair Via Mask Prediction

Automated program repair (APR) aims to fix software bugs without manual debugging efforts and plays a crucial role in software development and maintenance. Template-based APR has been widely investigated and shown promising results. However, it is challenging for template-based APR to select the appropriate donor code, which is an important repair ingredient for generating candidate patches. Inappropriate donor code may cause plausible but incorrect patch generation even with correct fix patterns, limiting the repair performance. In this paper, we aim to revisit template-based APR, and propose Gamma, to directly leverage large pre-trained language models for donor code generation. Our main insight is that instead of retrieving donor code in the local buggy file, we can directly predict the correct code tokens based on the context code snippets and repair patterns by a cloze task. Specifically, (1) Gamma revises a variety of fix templates from state-of-the-art template-based APR techniques (i.e., TBar) and transforms them into mask patterns. (2) Gamma adopts a pre-trained language model to predict the correct code for masked code as a fill-in-the-blank task. Although our idea is general and can be built on various existing pre-trained language models, we have implemented Gamma as a practical APR tool based on the recent UniXcoder model. The experimental results demonstrate that Gamma correctly repairs 82 bugs on Defects4J-v1.2, which achieves 20.59% (14 bugs) and 26.15% (17 bugs) improvement over the previous state-of-the-art template-based approach TBar and learning-based one Recoder. Furthermore, Gamma repairs 45 bugs and 22 bugs from the additional Defects4J-v2.0 and QuixBugs, indicating the generalizability of Gamma in addressing the dataset overfitting issue. We also prove that adopting other pre-trained language models can provide substantial advancement, e.g., CodeBERT-based and ChatGPT-based Gamma is able to fix 80 and 67 bugs on Defects4J-v1.2, indicating the scalability of Gamma. Overall, our study highlights the promising future of adopting pre-trained models to generate correct patches on top of fix patterns in practice.