EdSketch: execution-driven sketching for Java

Sketching is a relatively recent approach to program synthesis, which has shown much promise. The key idea in sketching is to allow users to write partial programs that have ''holes'' and provide test harnesses or reference implementations, and let synthesis tools create program fragments that fill the holes such that the resulting complete program has the desired functionality. Traditional solutions to the sketching problem perform a translation to SAT and employ CEGIS. While effective for a range of programs, when applied to real applications, such translation-based approaches have a key limitation: they require either translating all relevant libraries that are invoked directly or indirectly by the given sketch -- which can lead to impractical SAT problems -- or creating models of those libraries -- which can require much manual effort.

This paper introduces execution-driven sketching, a novel approach for synthesis of Java programs with respect to the given test suite using a backtracking search that is commonly employed in software model checkers. The key novelty of our work is to introduce effective pruning strategies to efficiently explore the actual program behaviors in presence of libraries and to provide a practical solution to sketching small parts of real-world applications, which may use complex constructs of modern languages, such as reflection or native calls. Our tool EdSketch embodies our approach in two forms: a stateful search based on the Java PathFinder model checker; and a stateless search based on re-execution inspired by the VeriSoft model checker. Experimental results show that EdSketch's performance compares well with the well-known SAT-based Sketch system for a range of small but complex programs, and moreover, that EdSketch can complete some sketches that require handling complex constructs.