Human-in-the-Loop Oracle Learning for Semantic Bugs in String Processing Programs

How can we automatically repair semantic bugs in string-processing programs? A semantic bug is an unexpected program state: The program does not crash (which can be easily detected). Instead, the program processes the input incorrectly. It produces an output which users identify as unexpected. We envision a fully automated debugging process for semantic bugs where a user reports the unexpected behavior for a given input and the machine negotiates the condition under which the program fails. During the negotiation, the machine learns to predict the user's response and in this process learns an automated oracle for semantic bugs. In this paper, we introduce Grammar2Fix, an automated oracle learning and debugging technique for string-processing programs even when the input format is unknown. Grammar2Fix represents the oracle as a regular grammar which is iteratively improved by systematic queries to the user for other inputs that are likely failing. Grammar2Fix implements several heuristics to maximize the oracle quality under a minimal query budget. In our experiments with 3 widely-used repair benchmark sets, Grammar2Fix predicts passing inputs as passing and failing inputs as failing with more than 96% precision and recall, using a median of 42 queries to the user.