PaReco: Patched Clones and Missed Patches among the Divergent Variants of a Software Family

Re-using whole repositories as a starting point for new projects is often done by maintaining a variant fork parallel to the original. However, the common artifacts between both projects are not always kept up to date. As a result, patches are not optimally integrated across the two projects, which may lead to sub-optimal maintenance between the variant and the original project. For example, a bug existing in both projects can be patched in one but not the other (we see this as a missed opportunity). Furthermore, different developers can manually patch the bug (we see this as effort duplication). This paper presents a tool (named PaReco) that relies on clone detection to mine cases of missed opportunity and effort duplication from a pool of updates. We analyzed 364 (source to target) variant pairs with 8,323 patches resulting in a curated dataset containing 1,116 cases of effort duplication and 1,008 cases of missed opportunities. As a result, we achieve a precision of 91%, recall of 80%, accuracy of 88%, and F1-score of 85%. Furthermore, we investigated the time interval between patches and found out that, on average, missed patches in the target variants have been introduced in the source variants 52 weeks earlier. Consequently, PaReco can be used to manage variability in ``time'' by automatically identifying interesting patches in later project releases to be backported to supported earlier releases.