Mason: Type- and Name-Guided Program Synthesis

Abstract

Object-oriented programs tend to be written using many common coding idioms, such as those captured by design patterns. While design patterns are useful, implementing them is often tedious and repetitive, requiring boilerplate code that distracts the programmer from more essential details. In this paper, we introduce Mason, a tool that synthesizes object-oriented programs from partial program pieces, and we apply it to automatically insert design patterns into programs. At the core of Mason is a novel technique we call type- and name-guided synthesis, in which an enumerative solver traverses a partial program to generate typing constraints; discharges constraints via program transformations guided by the names of constrained types and members; and backtracks when a constraint is violated or a candidate program fails unit tests. We also introduce two extensions to Mason: a non-local backtracking heuristic that uses execution traces, and a language of patterns that impose syntactic restrictions on missing names. We evaluate Mason on a suite of benchmarks to which Mason must add various well-known design patterns implemented as a library of program pieces. We find that Mason performs well when very few candidate programs satisfy its typing constraints and that our extensions can improve Mason's performance significantly when this is not the case. We believe that Mason takes an important step forward in synthesizing multi-class object-oriented programs using design patterns.