University of Salerno CODE SMELLS: RELEVANCE OF THE PROBLEM AND NOVEL DETECTION TECHNIQUES Fabio Palomba Athesissubmittedforthedegreeof Doctor of Philosophy December 2016 SOFTWARE ENGINEERING LAB,UNIVERSITY OF SALERNO HTTP://WWW.SESA.UNISA.IT This research was done under the supervision of Prof. Andrea De Lucia and Prof. Rocco Oliveto with the financial support of the University of Salerno and the Uni- versity of Molise, from January 1st of 2014 to December 31th of 2016. The final version of the thesis has been revised based on the reviews made by Prof. Michele Lanza and Prof. Jens Krinke. The doctoral committee was composed by: Prof. Dr. Filomena Ferrucci Chairperson, University of Salerno, Italy Prof. Dr. Giovanni Acampora University of Naples “Federico II”, Italy Prof. Dr. Anna Rita Fasolino University of Naples “Federico II”, Italy Prof. Dr. Michele Lanza University of Lugano, Switzerland First release, December 2016. Revised on March 2017. ii iii Some Preliminary Considerations and Acknowledgments I was lucky. I started my PhD already counting a quite important ASE paper (about the following cited HIST) that would became a TSE soon. In that period, I had my first meeting as a new PhD Student with my boss, Andrea De Lucia. I expected honey words, but I was surprised when he told me: “You did a good job, however the time of HIST is almost done. What’s next? What do you want to do after HIST?”. I was somehow shocked: I had no time to relax a bit after my good work, that I should have been already prepared for the next one. Only some months later, everything was clear. I got the real meaning of that words and I learned the lesson: success is a long and winding road, and the only way to grow up is to continue working hard. Above all, this is what I learned from Andrea. The second huge lesson is that “the sum of two good papers does not result in an excellent paper. You need to be focused on your objective, and provides a solution for a single problem per time”. With the years, I realized that this rule holds for all the important things of life: overacting just for the sake of showing how strong you are does not make sense without a well-defined goal. All in all, I believe that Andrea has been more than a “simple” advisor. At the same time I had a co-advisor, Rocco Oliveto. I spent most of my first PhD year at the University of Molise (at home, after all). I remember that during my first month I was working and I said to Rocco that I was in a hurry because iv of an upcoming deadline of an important conference, where I would have liked to submit a paper. That was a fault. I received a terrible scolding, because “you must not reason in terms of conferences, you must not think about the number of papers in your CV! You must simply work to do something good”. Today I can say that he was right, I was simply too impulsive and completely unprepared. Even if our relationship has been not always a bowl of cherries, I must thank Rocco because he balanced my ambitions with the awareness to have to keep always one’s feet on the ground. This is one of the main output of my PhD: as I said several times, all the PhD students should have a Rocco in their team. For several reasons, I must deserve a special thank to Gabriele Bavota. He held my hand when I was too young, and he learned me how to behave and how to be a good researcher. I academically grew up following the lessons learned by observing and talking with the people mentioned above. Thanks for all the effort spent and the sugges- tions you gave to me. I hope I have not disappointed the expectations. During these years, I also had the pleasure and the honor to work with some of the most important and prolific researchers of the world. Their contribution in my academic growth as well as in the research presented in this thesis cannot be described by words. For this reason, I must thank Massimiliano Di Penta, Denys Poshyvanyk, Annibale and Sebastiano Panichella, Fausto Fasano, Andrian Mar- cus, Mario Linares Vasquez, Filomena Ferrucci, Gemma Catolino, Harald Gall, Adelina Ciurumelea, Carmine Vassallo, Giovanni Grano, Damian Andrew Tam- burri, Elisabetta Di Nitto, Francesca Arcelli Fontana, Marco Zanoni, Mauricio Aniche, Luca Pascarella, Moritz Beller, Qianqian Zhu, Alberto Bacchelli, and Arie Van Deursen. I was lucky. I had the non-trivial opportunity to work together with friends, achieving some of the top results of my PhD. v Thanks to Michele Tufano: as I always said, the best of us. We passed from academic projects to the top of the world with the ICSE’15 Distinguished Paper Award. It was amazing, and I will never forget it. Thanks to Dario Di Nucci: I love thinking we brought (and we are bringing) some fresh air into areas that have not seen breakthroughs for some time. We touched the top several times, and I’m sure it will happen again. Thanks to Pasquale Salza: In all honestly, I will always remember him for the night before the submission of the ICSE’17 paper, where he carefully proofread every single word of the paper at 2 a.m., after a full day of (desperate) work. For- tunately, that paper was accepted: I am still really hoping that the acceptance was due to that careful proofreading. My PhD has been also composed of funny moments. Unfortunately, or per- haps fortunately, the SESA LAB has seen a lot of them. Anyway, I believe that the research group hosted in this laboratory has delivered more than the required and much more than the expected. I really hope to see this research group in the same laboratory again. For this reason, I really hope that the things will be easier in Italy, and in Salerno, soon. As I said, I was lucky. During my PhD, I had the pleasure to co-advise several Bachelor and Master Theses. Beyond doubts, students gave me more than they have received. For this reason, I want to thank Antonio Panariello, Felice D’Avino, Stefano Ferrante, Marco Moretti, Emilio Arvonio, Gilda Trezza, Gianmarco Del Pozzo, Santolo Tubelli, Davide De Chiara, Alessandro Longo, Fabio Soggia, Giuseppe De Rosa, Sandro Siravo, Antonio Prota, Fabiano Pecorelli, Elena Sollai, Michele Lotierzo, Salvatore Geremia, Pasquale Martiniello, Dustin Lim, and all the other students that had good (or even hard) times with me. As I already said, I was lucky. vi In a crisis period such as the one experienced by my country, and in particu- lar, by my University, I had the opportunity to travel quite a lot. Thanks to the University of Salerno and the University of Molise for having supported me. These trips gave me the opportunity to know and meet some important and somehow interesting characters of the research community. One of them is beyond doubts Michele Lanza. I knew him in Victoria during my first ICSME conference in 2014: on the Thursday before I left, he approached and said me important words that I hope he did not forget. After almost three years from that moment, he be- came one of the Reviewer of my PhD thesis. It has been a honor for me, and I hope that his final PhD Thesis review will always be in my mind during my future black periods (if any, and hopefully not). Once again, I was lucky. Up to now, I never sent a CV looking for a new position. This was also due to my visiting period at TU DELFT at the end of my second PhD year. During that period, I knew and had the honor to work together with Andy Zaidman. Afterwards, I don’t know why and I don’t know what he saw in me, but the fact is that he asked me to join TU DELFT for my post-doc: I accepted. I will be always grateful to Andy for the opportunity he gave to me. Besides being a (great) critique reviewer, and therefore a great advisor, Andy has also an enviable calm when facing every daily problem (even the more complex one). I really hope to get from him at least a 1% of his enormous qualities. I was extremely lucky. During my life as a PhD Student, I lived in a very small town close to the Uni- versity. I always felt at home: who is not born around that town or that region can- not understand what I mean. One of the main reason for this statement (besides the food, of course) is the presence of an “additional family” who always waited for me after a workday (physically or not). Alessandro who cooked me some hot foods when I was late for dinner. Luigi, for having caused several delays because vii of his long showers. Cosmo who became a (non-properly, but still valuable) mas- terchef for me. Elisa, who deserved to me some – sometimes right, sometimes wrong – scolding as well as some conversations abount life and future. Dario, for the philosophical conversations to keep always around a beer. Pasquale, for the amazing ideas which came after having drunk too much drinks (and also for the amazing time I spent seeing him after drunk too much drinks). Ciro, for the strength to carry on although the problems. Enrico, who will be always part of my heart. Cristina, who is my preferred (no matters that she is the one) “sister in law”.