Refactoring Mining - The key to unlock software evolution

Keynote at the International Workshop on Refactoring
co-located with the 36th IEEE/ACM International Conference on Automated Software Engineering (ASE '21)
November 14, 2021

Transcript

1. Refactoring Mining The key to unlock software evolution Nikolaos Tsantalis Concordia University
2. Thank you IWoR
3. Who am I RefactoringMiner
4. Refactoring Miner
5. Alexander Chatzigeorgiou Eleni Stroulia Zhenchang Xing Fabio Rocha
6. CASCON'13 version 0.0
7. • Ideas inspired from UMLDiff • Structure of method bodies is ignored • Method body includes only method calls and field accesses • Most refactorings detected based on signature matching • Only precision is provided • Evaluation included only 3 systems
8. Refactoring motivations
10. Why did I stop working on this research? Ref-Finder (ICSM 2010): "The precision and recall on open source projects were 0.74 and 0.96 respectively." "Since these programs did not document refactorings, we created a set of correct refactorings by running REF-FINDER with a similarity threshold (σ=0.65) and manually verified them. We then measured a recall by comparing this set with the results found using a higher threshold (σ=0.85)"
11. Lesson # 1 Don't be intim ida te d by s u p e r re sults Always que stion the results
12. Until one day... Danilo Silva Marco Tulio Valente
13. Where was the code?
14. Lesson #2 Always make your code & data available in a repository You never know what it can enable in the future
15. Open Science initiatives M. T. Baldassarre, N. Ernst, B. Hermann, T. Menzies, R. Yedida Mandatory Data Availability field
16. Let's do an empirical study about refactoring We must study Why We Refactor
17. ICSE'16 version 0.1
18. • Danilo developed the API of RefactoringMiner • Tooling for checking out and parsing Git commits • Infrastructure for monitoring GitHub projects • Automatic generation of emails to contact developers • A web app for thematic analysis
19. Firehouse interview • Monitored 124 GitHub projects between June 8th and August 7th, 2015 • Sent 465 emails and received 195 responses (42%) • +27 commits with a description explaining the reasons • Compiled a catalogue of 44 distinct motivations for 12 well-known refactoring types
20. Motivation Catalogue Artifact https://github.com/aserg- ufmg/why-we-refactor
21. ICSE'16 rejection Reviewer #1: "A major threat to the research is not discussed or considered, that RefFinder has poor recall (0.24 [31]). The authors did a good job of combating the low-precision by manually inspecting results, the low recall is not discussed or dealt with."
22. Lesson #3 Even ICSE reviewers make mistakes Don't get disappointed. Improve, advance, re-submit
23. FSE'16 re-submission • Renamed the tool from RefDetector to RefactoringMiner • Addressed most of reviewers' comments
25. RefDiff MSR'17 RefactoringMiner ...
26. The path of Virtue or Vice
27. Rebirth ICSE’18 version 1.0
28. Limitations of previous approaches 1. Dependence on similarity thresholds • thresholds need calibration for projects with different characteristics 2. Dependence on built versions • only 38% of the change history can be successfully compiled [Tufano et al., 2017] 3. Unreliable oracles for evaluating precision/recall • Incomplete (refactorings found in release notes or commit messages) • Biased (applying a single tool with two different similarity thresholds) • Artificial (seeded refactorings)
29. Thresholds are banned
30. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } After Before
31. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static List<Address> createAddresses(int count) { List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } After Before
32. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } After Before private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", ports.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; }
33. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } After Before private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", ports.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; }
34. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { } return addresses; } try { addresses[i] = new Address("127.0.0.1", ports.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } After Before
35. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { addresses.add(createAddress("127.0.0.1", ports.incrementAndGet())); } return addresses; } protected static Address createAddress(String host, int port) { try { return new Address(host, port); } catch (UnknownHostException e) { e.printStackTrace(); } return null; } After Before
36. protected static Address createAddress(String host, int port) { try { return new Address(host, port); } catch (UnknownHostException e) { e.printStackTrace(); } return null; } private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { addresses.add(createAddress("127.0.0.1", ports.incrementAndGet())); } return addresses; } After Before textual similarity ≈ 30%
37. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { addresses.add(createAddress("127.0.0.1", ports.incrementAndGet())); } return addresses; } protected static Address createAddress(String host, int port) { try { return new Address(host, port); } catch (UnknownHostException e) { e.printStackTrace(); } return null; } After Before (1) Abstraction
38. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { addresses.add(createAddress("127.0.0.1", ports.incrementAndGet())); } return addresses; } protected static Address createAddress(String host, int port) { try { return new Address(host, port); } catch (UnknownHostException e) { e.printStackTrace(); } return null; } After Before (1) Abstraction
39. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { addresses.add(createAddress("127.0.0.1", ports.incrementAndGet())); } return addresses; } protected static Address createAddress(String host, int port) { try { return new Address(host, port); } catch (UnknownHostException e) { e.printStackTrace(); } return null; } After Before (2) Argumentization
40. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { addresses.add(createAddress("127.0.0.1", ports.incrementAndGet())); } return addresses; } protected static Address createAddress(String host, int port) { try { return new Address("127.0.0.1", ports.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } return null; } After Before (2) Argumentization
41. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { addresses.add(createAddress("127.0.0.1", ports.incrementAndGet())); } return addresses; } protected static Address createAddress(String host, int port) { try { return new Address("127.0.0.1", ports.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } return null; } After Before (3) AST Node Replacements
42. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { addresses.add(createAddress("127.0.0.1", ports.incrementAndGet())); } return addresses; } protected static Address createAddress(String host, int port) { try { return new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } return null; } After Before (3) AST Node Replacements
43. private static Address[] createAddresses(int count) { Address[] addresses = new Address[count]; for (int i = 0; i < count; i++) { try { addresses[i] = new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } } return addresses; } private static List<Address> createAddresses(AtomicInteger ports, int count){ List<Address> addresses = new ArrayList<Address>(count); for (int i = 0; i < count; i++) { addresses.add(createAddress("127.0.0.1", ports.incrementAndGet())); } return addresses; } protected static Address createAddress(String host, int port) { try { return new Address("127.0.0.1", PORTS.incrementAndGet()); } catch (UnknownHostException e) { e.printStackTrace(); } return null; } After Before textual similarity = 100%
44. Reliable oracle • We used the “Why We Refactor” dataset (538 commits from 185 open source projects) • We executed both available tools (RefactoringMiner and RefDiff) • Converted the output of the tools to the same format • We manually validated all refactoring instances (4,108 unique instances, out of which 3,188 were true positives and 920 were false positives) • The validation process was labor-intensive and involved 3 validators for a period of 3 months (i.e., 9 person-months) • To compute recall, we considered the union of the true positives reported by both tools as the ground truth. Matin Mansouri Laleh Eshkevari Davood Mazinanian
47. ICSE’18 retrospective • Our solution was still far from perfect • Time pressure • It was urgent to establish RefactoringMiner with a publication • ICSE deadline: August 25, 2017 • Sophia’s birth: August 15, 2017 • Despite working over 1 year on this paper, there was still space for improvement • The entire team graduated after this work
48. Wisdom TSE’20 version 2.0
49. • Added more replacement types • 20 new sub-method level refactoring types detected based on AST node replacements • Nested refactoring detection • Refactoring inference • Improved the matching of method calls to method declarations with argument type inference
50. Even more reliable oracle • We executed all available tools • RefactoringMiner 1.0 and 2.0 • RefDiff 0.1.1, 1.0, 2.0 • GumTreeDiff 2.1.2 • Converted the output of the tools to the same format • We validated 5,830 new unique refactoring instances, out of which 4,038 were true positives and 1,792 were false positives. • 7,226 true positives in total for 40 different refactoring types (72% of true instances are detected by two or more tools) Ameya Ketkar
53. Emperor version 2.2
54. From loop and if to Stream API .forEach() and .filter()
55. Current status • 85 supported refactoring types • 10,900 validated true positives in the oracle • Precision: 99.7% • Recall: 97% • Most tested and reliable version (200K commits without exception) • Independent studies confirm it has the best precision
56. Lesson #4 What it takes to make a reliable & usable tool Minimum 5 years of research and development Extensive testing Detailed documentation (README with API code snippets) Supporting users (200+ issues resolved) Stable project leader Great team
57. The promises
58. Promise #1 “researchers can replicate existing empirical studies and refute or confirm previously-held beliefs.”
60. Threats to validity • Both studies relied on Ref-Finder • Independent studies revealed that Ref-Finder had low precision/recall • 35% precision, 24% recall [Soares et al. JSS 2013] • 27% precision [Kádár et al. PROMISE 2016] • Ref-Finder paper claimed 74% precision, 96% recall • Collected refactoring info at release level (between two versions) • Coarse-grained analysis led to strong and unsafe assumptions
62. Lesson #5 A tool comes with a huge responsibility for its authors We should go above and beyond when evaluating its accuracy
63. Promise #2 “reduce the noise created by refactorings, such as file/directory renaming, and significantly improve the accuracy of other tools.”
65. Lesson #6 Making existing code evolution analysis techniques refactoring-aware can improve their accuracy
66. Promise #3 “our oracle of true refactorings from 538 commits across 185 projects provides an invaluable resource for validating novel refactoring tools and for comparing existing approaches”
68. Promise #4 “enable online refactoring detection on partial input, when a developer inspects a code diff to review a change, or tries to understand code evolution selectively”
69. • Partially refactoring-aware • Supports method signature changes • Method moves • File renames/moves • Uses thresholds when comparing program elements, calibrated on a training set of 100 methods • Mismatches methods from which a significant part of their body has been extracted to new methods, as it uses a 75% body similarity threshold to match modified methods • Ultra-fast: Less than 2 seconds to fetch the entire change history of a method
70. Challenge How can we take advantage of RefactoringMiner accuracy in a way that is not computationally expensive? Mehran Jodavi Solution Partial and incremental commit analysis based on the location of the tracked program element
71. Precision +7.5% Recall +3.7% Precision +9.1% Recall +5.8% > 97% precision/recall change level Method tracking commit level Method tracking change level Variable tracking > 98% precision/recall commit level
72. Promise #5 “Integrating RefactoringMiner with the diff and code review tools can raise the level of abstraction for code changes originating from refactorings, thus helping developers better understand the code evolution”
73. Diff Hunk Graph Nodes: diff hunks Hard links: syntactic constraints between the AST nodes Soft links: repetitive change patterns Refactoring links: edits in different locations originating from the same refactoring Cosmetic links: changes in comments & reformatting
74. Promise #6 “refactoring operations can be automatically documented at commit-time to provide a more detailed description of the applied changes in the commit message”
77. Mining for Learning
79. File f = new File(:[v0], :[v1]) → Path f = :[v0].resolve(:[v1]) FileOutputStream stream = new FileOutputStream(:[v0]) → OutputStream stream = Files.newOutputStream(:[v0]) → Ameya Ketkar Rewrite rules
81. Mining for Recommending
82. Why We Refactor++ A large-scale empirical study • We developed detection rules for refactoring motivations • We optimized the rules on the FSE’16 “Why We Refactor” dataset • We validated their accuracy on the TOSEM’2020 dataset • Precision: 98.4% Recall: 93.5% • We collected the motivations for 346K Extract Method instances found in 132,897 commits of 325 open-source repositories Sadegh Aalizadeh J. Pa ntiuchina , F. Za m pe tti, S. Sca la brino, V. Pia nta dosi, R. Olive to, G. Bavota , a nd M. Di Pe nta , "Why Deve lope rs Re fa ctor Source Code : A Mining-ba se d Study,“ ACM Tra nsa ctions on Softwa re Engine e ring a nd Me thodology, Volum e 29, Issue 4, Article 29, Se pte m be r 2020.
84. Refactoring recommendation tools for top-5 Extract Method motivations 1. Reusable Method [NONE] 2. Remove Duplication [CeDAR (Tairas and Gray, IST’12), Creios (Hotta et al., CSMR’12), Rase (Meng et al., ICSE’15), JDeodorant (Tsantalis et al., TSE’15 + ICSE’17), CRec (Yue et al., ICSME’18)] 3. Facilitate Extension [FR-Refactor (Ally S. Nyamawe et al. RE’19 + EMSE’20)] 4. Decompose for Readability [JDeodorant (Tsantalis and Chatzigeorgiou, JSS’11), JExtract (Silva et al., ICPC’14), SEMI (Charalampidou et al., TSE’17), GEMS (Xu et al., ISSRE’17)] 5. Alternative Signature [NONE]
85. Mining for Accuracy
88. Making better refactoring mining tools is a community effort Mining competitions hosted in the Workshop Community-created benchmarks Hackathons for improving tools
89. https://github.com/tsantalis/RefactoringMiner https://github.com/JetBrains-Research/RefactorInsight https://github.com/JetBrains-Research/kotlinRMiner https://github.com/JetBrains-Research/data-driven-type-migration Oleg Smirnov Ameya Ketkar Zarina Kurbatova https://github.com/jodavimehran/code-tracker Mehran Jodavi