Completeness of Composite Refactorings for Smell Removal

Code smells are problems in the internal structural quality. Refactoring is a technique commonly used to remove code smells. A single refactoring rarely suffices to assist developers in achieving a full removal of a code smell. Thus, developers frequently apply composite refactorings (or, simply, composites) with the goal of fully removing a smell. A composite is formed by two or more interrelated single refactorings. Studies report that developers often fail in fully removing code smells through composite refactoring. In this context, a composite refactoring is considered incomplete whenever it does not fully remove a smell. Either incomplete or complete composite is formed by several refactorings; thus, both may inadvertently degrade other parts of the software. However, the literature on (in)complete composites and their effects on structural quality is still scarce. This lack of knowledge hampers the design of empirically-based recommendations to properly assist developers in performing effective complete composites, i.e., those not causing any harm in related parts of the program. This doctoral research investigates the effect of composite (in)completeness on structural quality and proposes a catalog with composite recommendations for the full removal of popular code smell types. We investigated 618 composites in 20 software projects. We found that 58% of incomplete composites did not change the internal structural quality, and 64% of complete composites are formed by refactoring types that were not actually previously recommended in the literature or elsewhere. The expected contributions are a list of findings, guidelines, and a catalog to support developers on how to successfully perform complete composites.