TS4J: a fluent interface for defining and computing typestate analyses

Typestate analyses determine whether a program's use of a given API obeys this API's usage constraints in the sense that the right methods are called on the right objects in the right order. Previously, we and others have described approaches that generate typestate analyses from textual finite-state property definitions written in specialized domain-specific languages. While such an approach is feasible, it requires a heavyweight compiler, hindering an effective integration into the programmer's development environment and thus often also into her software-development practice. Here we explain the design of a pure-Java interface facilitating both the definition and evaluation of typestate analyses. The interface is fluent, a term coined by Eric Evans and Martin Fowler. Fluent interfaces provide the user with the possibility to write method-invocation chains that almost read like natural-language text, in our case allowing for a seemingly declarative style of typestate definitions. In all previously described approaches, however, fluent APIs are used to build configuration objects. In this work, for the first time we show how to design a fluent API in such a way that it also encapsulates actual computation, not just configuration. We describe an implementation on top of Soot, Heros and Eclipse, which we are currently evaluating together with pilot customers in an industrial context at Fraunhofer SIT.