An Empirical Study Osaka, 2016-03-16 Stefan Wagner On the Relationship of Inconsistent Software Clones and Faults 

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Technische Universität München 

Class A Class B 

Class A Class B 

Class A Class B 

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Often 20%–30% redundancy 

Inconsistencies Can you spot the difference? 

Types of Clones Type 1 an exact copy without modifications (except for whitespace and comments) Type 2 a syntactically identical copy; only variable, type, or function identifiers have been changed Type 3 a copy with further modifications; statements have been changed, added, or removed 

How problematic are these inconsistencies? Indicating harmfulness Inconsistent evolution of clones in industrial telecom. SW. [Lague97] Higher revision number for files with clones in legacy SW. [Monden02] Substantial amount of coupled changes to code clones. [Kim05] Discovery of bugs through search for inconsistent clones or clone evolution analysis. [Li06], [SuChiu07], [Aversano07], [Bakota07] Every other unintentional inconsistency constitutes a fault as judged by developers [Juergens09] Doubting harmfulness Failure to statistically verify impact of clones on change couplings [Geiger06] Inconsistent clones hardly ever become consistent later. [Krinke07] Failure to statistically verify impact of clones on changeability. [Lozano08] Most changes intentionally inconsistent [Göde11] No statistically significant impacts on faults [RahmanBirdDevanbu12] 

Developers’ awareness of clones is an important factor in the clones’ harmfulness. 

Case Study Design 

Research Questions RQ1: Do software systems contain type-3 clones? |CT3| / |C| RQ2: Do type-3 clones contain documented faults? |CT3 F| / |CT3| RQ3: Are developers aware of type-3 clones? |IMS| / |IM|, interviews with key developers Clone Groups C (exact and incons.) Inconsistent clone groups CT3 Faulty clone Groups CT3 F 

Cases System Size (KLOC) Age (Years) Developers A 253 4 10 B 332 5 5 C 454 4 10 Java Automotive domain 

Data Collection and Analysis ort HTML Dash- board v1 v2 v3 Extract Analyse Query for relationships and evolution Extract Interviews with developers Transcribe Coding 

Results 

Quantitative Results System A B C Overall Share of type-3 clones 0.56 0.23 0.79 0.52 Share of faulty clone type-3 classes 0.33 0.05 0.03 0.17 Share of simultaneously modified type-3 clones 0.58 0.89 0.92 0.85 

Qualitative Results System A B C General clone awareness x No general clone awareness x x No specific clone awareness x x No clone check while bug fixing x x Clone warning while developing x Common code ownership x Discussion about co-changes x 

Conclusions 

Developer awareness and faultiness varies. Half of the clone groups are type-3 Rate of faulty type-3 clones ~17 % Future studies should look at awareness! Conclusions 

Developers’ awareness of clones is an important factor in the clones’ harmfulness. 

Prof. Dr. Stefan Wagner e-mail [email protected] phone +49 (0) 711 685-88455 WWW www.iste.uni-stuttgart.de/se Twitter prof_wagnerst ORCID 0000-0002-5256-8429 Institute of Software Technology Slides are available at www.stefan-wagner.biz. Joint work with Asim Abdulkhaleq, Kamer Kaya and Alexander Paar 

Pictures Used in this Slide Deck „Clones“ by Nick Royer (https://flic.kr/p/d1DFPL) Happy Programmers by Jesper Ronn-Jensen (https://flic.kr/p/oi9kA) „Mercurial Logo“ by Mackall (http://www.selenic.com/hg-logo/)