Constraint-Based Refactoring

Constraint-based refactoring generalizes constraint-based type refactoring as introduced by Tip et al. [61] by extending the coverage of change from types to names, locations, accessibilities, and other properties of program elements. Starting with a generic specification of refactoring tools, we systematically develop constraint-based refactoring as a generic solution to a certain class of refactoring problems and provide a condition under which constraint-based refactoring tools are proven correct for any given target language. Although compliance with this correctness condition is hard to prove for target languages whose semantics is not formally defined, we show how the condition gives rise to automated testing procedures. We present a novel algorithm based on constraint-logic programming for the generation of constraints from a program to be refactored, and demonstrate its time and space requirements by using it in the application of refactorings to open source programs. Summarizing earlier work, we show how the principles underlying constraint-based refactoring tools extend to ad hoc refactoring, cross-language refactoring, and model/code co-refactoring.