Flexeme: Untangling Commits Using Lexical Flows

Profir-Petru Pârțachi, Santanu Kumar Dash, Miltiadis Allamanis, Earl T. Barr

Abstract:

Today, most developers bundle changes into commits that they sub-
mit to a shared code repository. Tangled commits intermix distinct
concerns, such as a bug fix and a new feature. They cause issues
for developers, reviewers, and researchers alike: they restrict the
usability of tools such as git bisect, make patch comprehension
more difficult, and force researchers who mine software reposi-
tories to contend with noise. We present a novel data structure,
the 𝛿-NFG, a multiversion Program Dependency Graph augmented
with name flows. A 𝛿-NFG directly and simultaneously encodes dif-
ferent program versions, thereby capturing commits, and annotates
data flow edges with the names/lexemes that flow across them. Our
technique, Flexeme, builds a 𝛿-NFG from commits, then applies
Agglomerative Clustering using Graph Similarity to that 𝛿-NFG to
untangle its commits. At the untangling task on a C# corpus, our
implementation, Heddle, improves the state-of-the-art on accuracy
by 0.14, achieving 0.81, in a fraction of the time: Heddle is 32 times
faster than the previous state-of-the-art.