Bug-proneness and late propagation tendency of code clones: A Comparative study on different clone types

According to our experimental results on thousands of revisions of nine diverse subject systems, Type 3 clones exhibit the highest bug-proneness among the three clone-types. The bug-proneness of Type 1 clones is the lowest. Also, Type 3 clones have the highest likeliness of being co-changed consistently while experiencing bug-fixing changes. Moreover, the Type 3 clones that experience bug-fixes have a higher possibility of evolving following a Similarity Preserving Change Pattern (SPCP) compared to the bug-fix clones of the other two clone-types. From the experimental results it is clear that Type 3 clones should be given a higher priority than the other two clone-types when making clone management decisions. Our investigation on the relatedness between bug-proneness and late propagation in code clones implies that bug-proneness of code clones is not primarily related with late propagation. The possibility that a bug-fix experienced by a clone fragment will be related with late propagation is only 1.4%. Moreover, for only 10.76% of the cases, a late propagation experienced by clone fragments can be related with a bug. Thus, late propagation contributes to a very little proportion of the bugs in code clones. We believe that our study provides useful implications for ranking clones for management such as refactoring and tracking.