Automatic Test-Case Reduction in Proof Assistants: A Case Study in Coq
This addresses the need for Coq developers to quickly handle compatibility issues, though it is incremental as it adapts existing test-case reduction techniques to a new domain.
The paper tackles the problem of efficiently identifying and fixing compatibility issues in proof assistants by presenting the Coq Bug Minimizer, a tool that reduces buggy test cases to minimal standalone files, succeeding in 75% of cases and reducing size by about two-thirds with an average compile time of 1.25 seconds.
As the adoption of proof assistants increases, there is a need for efficiency in identifying, documenting, and fixing compatibility issues that arise from proof assistant evolution. We present the Coq Bug Minimizer, a tool for reproducing buggy behavior with minimal and standalone files, integrated with coqbot to trigger automatically on Coq reverse CI failures. Our tool eliminates the overhead of having to download, set up, compile, and then explore and understand large developments: enabling Coq developers to easily obtain modular test-case files for fast experimentation. In this paper, we describe insights about how test-case reduction is different in Coq than in traditional compilers. We expect that our insights will generalize to other proof assistants. We evaluate the Coq Bug Minimizer on over 150 CI failures. Our tool succeeds in reducing failures to smaller test cases in roughly 75% of the time. The minimizer produces a fully standalone test case 89% of the time, and it is on average about one-third the size of the original test. The average reduced test case compiles in 1.25 seconds, with 75% taking under half a second.