WitchDoctor: IDE support for real-time auto-completion of refactorings

Integrated Development Environments (IDEs) have come to perform a wide variety of tasks on behalf of the programmer, refactoring being a classic example. These operations have undeniable benefits, yet their large (and growing) number poses a cognitive scalability problem. Our main contribution is WitchDoctor - a system that can detect, on the fly, when a programmer is hand-coding a refactoring. The system can then complete the refactoring in the background and propose it to the user long before the user can complete it. This implies a number of technical challenges. The algorithm must be 1) highly efficient, 2) handle unparseable programs, 3) tolerate the variety of ways programmers may perform a given refactoring, 4) use the IDE's proven and familiar refactoring engine to perform the refactoring, even though the the refactoring has already begun, and 5) support the wide range of refactorings present in modern IDEs. Our techniques for overcoming these challenges are the technical contributions of this paper. We evaluate WitchDoctor's design and implementation by simulating over 5,000 refactoring operations across three open-source projects. The simulated user is faster and more efficient than an average human user, yet WitchDoctor can detect more than 90% of refactoring operations as they are being performed - and can complete over a third of refactorings before the simulated user does. All the while, WitchDoctor remains robust in the face of non-parseable programs and unpredictable refactoring scenarios. We also show that WitchDoctor is efficient enough to perform computation on a keystroke-by-keystroke basis, adding an average overhead of only 15 milliseconds per keystroke.