Verification Modulo Tested Library Contracts
For developers of verified software, this work provides a method to automate client verification by inferring contracts that are both provably sufficient and testable, reducing manual effort.
The paper addresses the problem of automating verification of client programs using complex libraries by synthesizing modular contracts for library methods that are adequate to prove the client correct and pass testing. The tool VMTLC demonstrates efficacy on benchmarks with large libraries.
We consider the problem of \emph{verification modulo tested library contracts} as a step towards automating the verification of client programs that use complex libraries. We formulate this problem as the synthesis of modular contracts for the library methods used by the client that are adequate to prove the client correct, and that also pass the scrutiny of a testing engine that tests the library against these contracts. We also consider a new form of method contracts called \emph{contextual contracts} that arise in this setting that hold in the context of the client program, and can often be simpler and easier to infer than classical modular contracts. We provide a counterexample-guided learning framework to solve this problem, in which the synthesizer interacts with a constraint solver as well as the testing engine in order to infer adequate modular/contextual method contracts and inductive invariants for the client. The main synthesis engines we use are generalizing CHC solvers that are realized using ICE learning algorithms. We realize this framework in a tool called \vmtlc and show its efficacy on benchmarks where clients call large libraries.