Bench4BL: Reproducibility Study on the Performance of IR-Based Bug Localization

1. Bench4BL: Reproducibility Study on the Performance of IR-Based Bug Localization Jaekwon Lee1, Dongsun Kim1, Tegawendé F. Bissyandé1,   Woosung Jung2, Yves Le Traon1 1SnT, University of Luxembourg - Luxembourg 2Seoul National University of Education - South Korea

2. Bug Localization !2

3. Bug Localization !3 Where should we ﬁx?

4. Bug Localization !4 Model ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java Bug Report ……….. …. ….. …..…. ……..  …. .. ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java A set of code ﬁles Bug Localization

5. F(x) Test Case Test Case Test Case 01: MultiMap<Method, Long> duration = new MultiMap<Method, Long>(); 02: // run all benchmarks in same order, recording duration 03: for (Method m : benchmarks) { 04: System.err.println("# "+m.getName()+" benchmarking"); 05: List<Integer> reps = getReps(min_reps, m); 06: for (int r : reps) { 07: System.gc(); 08: long start = System.nanoTime(); 09: m.invoke(suite,r); 10: long stop = System.nanoTime(); 11: duration.map(m, stop - start); 12: } 13: } Function 01: MultiMap<Method, Long> duration = new MultiMap<Method, Long>(); 02: // run all benchmarks in same order, recording duration 03: for (Method m : benchmarks) { 04: System.err.println("# "+m.getName()+" benchmarking"); 05: List<Integer> reps = getReps(min_reps, m); 06: for (int r : reps) { 07: System.gc(); 08: long start = System.nanoTime(); 09: m.invoke(suite,r); 10: long stop = System.nanoTime(); 11: duration.map(m, stop - start); 12: } 13: } Function Fault Localization Bug Localization !5 Bug Localization Model ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java Bug Report ……….. …. ….. …..…. ……..  …. .. ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java A set of code ﬁles

6. Bug Localization F(x) Test Case Test Case Test Case 01: MultiMap<Method, Long> duration = new MultiMap<Method, Long>(); 02: // run all benchmarks in same order, recording duration 03: for (Method m : benchmarks) { 04: System.err.println("# "+m.getName()+" benchmarking"); 05: List<Integer> reps = getReps(min_reps, m); 06: for (int r : reps) { 07: System.gc(); 08: long start = System.nanoTime(); 09: m.invoke(suite,r); 10: long stop = System.nanoTime(); 11: duration.map(m, stop - start); 12: } 13: } Function 01: MultiMap<Method, Long> duration = new MultiMap<Method, Long>(); 02: // run all benchmarks in same order, recording duration 03: for (Method m : benchmarks) { 04: System.err.println("# "+m.getName()+" benchmarking"); 05: List<Integer> reps = getReps(min_reps, m); 06: for (int r : reps) { 07: System.gc(); 08: long start = System.nanoTime(); 09: m.invoke(suite,r); 10: long stop = System.nanoTime(); 11: duration.map(m, stop - start); 12: } 13: } Function Fault Localization Bug Localization !6 Model ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java Bug Report ……….. …. ….. …..…. ……..  …. .. ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java ….. …..….. …..….. …..….. ….…..Java A set of code ﬁles

7. …..….. …..….. …..….. …..….. …..….. Source   Codes ……..…….. ……. …….. …..…….. ……..…….. …….. ……. Bug Report Information Retrieval based Bug Localization (IRBL) !7

8. …..….. …..….. …..….. …..….. …..….. Source   Codes ……..…….. ……. …….. …..…….. ……..…….. …….. ……. Bug Report NL tokens Code elements Meta Info. NL tokens Code elements Meta Info. Extracting Features Extracting Features Information Retrieval based Bug Localization (IRBL) !8

9. Feature  Vector …..….. …..….. …..….. …..….. …..….. Source   Codes ……..…….. ……. …….. …..…….. ……..…….. …….. ……. Bug Report …. Feature   Vectors NL tokens Code elements Meta Info. NL tokens Code elements Meta Info. Extracting Features Extracting Features Information Retrieval based Bug Localization (IRBL) !9

10. Feature  Vector …..….. …..….. …..….. …..….. …..….. Source   Codes ……..…….. ……. …….. …..…….. ……..…….. …….. ……. Bug Report Recommend  Code Files ….. …..….. …..….. …..….. ….. …..….. …..….. …..….. ….. …..….. …..….. …..….. ….. …..….. …..….. …..….. 1 2 3 N …. …. Feature   Vectors NL tokens Code elements Meta Info. NL tokens Code elements Meta Info. Extracting Features Extracting Features Comparing Similarity  & Ranking Information Retrieval based Bug Localization (IRBL) !10

11. !11 Is there any issue?

12. !12 Are these results mature enough? Not enough maturity of performance Subjects BRTracer BLUiR AmaLgam Locus ZXing 0.445 0.380 0.410 0.502 SWT 0.467 0.560 0578 0.640 AspectJ 0.264 0.263 0.271 0.320 PDE 0.367 0.349 0.322 0.422 JDT 0.232 0.277 0.282 0.359 (metric : MAP)

13. Are the subjects still usable? !13 PDE Eclipse ZXing AspectJ JDT SWT 98 286 20 #Reports Period 2004 - 2016 2004 - 2010 2002 - 2006 2010 - 2010 Subject Out-of-dated subjects 60 98

14. Are the subjects still usable? !14 PDE Eclipse ZXing AspectJ JDT SWT 98 286 20 #Reports Period 2004 - 2016 2004 - 2010 2002 - 2006 2010 - 2010 Subject Out-of-dated subjects 60 98

15. Evaluation Conﬁguration? !15 Inconsistent evaluation settings BugLocator BLIA Locus AmaLgam BRTracer BLUiR Version Matching Test ﬁle inclusion

16. Study Design !16

17. Experiment   Data Set RQ1: To what extent do IRBL techniques perform on up-to-date subjects? Research Questions !17

18. Experiment   Data Set Experiment Conﬁguration RQ1: To what extent do IRBL techniques perform on up-to-date subject? RQ2: What is the impact of version matching on the performance of IRBL techniques? RQ3: To what extent are IRBL techniques sensitive to the inclusion of test code ﬁles? Research Questions !18

19. Experiment   Data Set Experiment Conﬁguration Potential Improvement RQ1: To what extent do IRBL techniques perform on up-to-date subject? RQ2: What is the impact of version matching on the performance of IRBL techniques? RQ3: To what extent are IRBL techniques sensitive to the inclusion of test code ﬁles? RQ4: What potential performance gain can be reached by leveraging duplicate bug reports? Research Questions !19

20. BugLocator  (ICSE 2012) BLIA  (APSEC 2015) Locus  (ICSE 2016) AmaLgam  (ICPC 2014) BRTracer  (ICSME 2014) BLUiR  (ASE 2013) IRBL Features Sub Modules Bug report fixing historyFull text Code  segmentations Identifiers Identifiers Identifiers Identifiers Bug report fixing history Bug report fixing history, Revision history Revision history Bug report fixing history  Stack Trace Analysis, Revision history Bug report fixing history,   Stack Trace Analysis IRBL Techniques we used !20

21. Subjects !21 20+ Written in Java Publicly available bug reports 20 source code ﬁles   in one of its version

22. Subjects 46  Projects New Subjects 9,459   Bug Reports ……….. …. ….. …..…. ……..  …. .. 5  Projects 558   Bug Reports ……….. …. ….. …..…. ……..  …. .. Old Subjects !22

23. Subjects 46  Projects New Subjects 690   Major Versions 9,459   Bug Reports ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. 807   Duplicate Reports 5  Projects 5   Major Versions 558   Bug Reports ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. 136   Duplicate Reports Old Subjects !23

24. !24 ……….. …. ….. …..…. ……..  …. .. …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. Bug Oracle New Subjects Old Subjects ……….. …. ….. …..…. ……..  …. .. …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. Bug Oracle VS. Single version matching Test ﬁle included Conﬁguration RQ1:   The use of old vs. new subjects

25. Single version Matching Multiple version Matching !25 VS. Conﬁguration New subjects Test ﬁles included RQ2:   The importance of version matching

26. !26 ……….. …. ….. …..…. ……..  …. .. …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. Bug Oracle Test File Included Test File Excluded VS. +Test ……….. …. ….. …..…. ……..  …. .. …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. Bug Oracle CAMEL-12558: Transacted and Policy should not have outputs M main/java/org/apache/camel/model/PolicyDefinition.java M main/java/org/apache/camel/model/TransactedDefinition.java A test/java/org/apache/camel/catalog/CamelCatalog.java A main/java/org/apache/camel/tools/apt/CoreEipAnnotationPrint.java Added camel-web3j Spring-boot test A test/java/org/apache/camel/itest/springboot/CamelWeb3jTest.java    Update GoogleBigQueryProducer.java M main/java/org/apache/camel/component/GoogleBigQueryProducer.java Configuration Multiple version matching New subjects Commit Log RQ3:   The impact of test file inclusion

27. !27 Master reports Merged reportsDuplicate reports ……….. …. ….. …..…. ……..  …. .. …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. Bug Oracle   (Master reports) ……….. …. ….. …..…. ……..  …. .. …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. Bug Oracle   (Duplicate reports) Bug Oracle   (Merged reports) …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java …..….. …..….. …..….. …..….….. Java ……….. …. ….. …..…. ……..  …. .. …..…. ……..  …. ……….. …. ….. …..…. ……..  …. .. …..…. ……..  …. ……….. …. ….. …..…. ……..  …. .. …..…. ……..  …. Conﬁguration For the all subjects  Including test ﬁles in Bug Oracle RQ4:   Leveraging duplicate bugs reports

28. Experiment Results !28

29. Metrics MAP MRR MAP = 1 M MX j=1 AP(j) MRR = 1 M MX i=1 1 f-ranki MAP = 1 M MX j=1 AP(j) MRR = 1 M MX i=1 1 f-ranki !29 Mean Average Precision Mean Reciprocal Rank

30. ●● ●● 0.359 0.35 0.359 0.365 0.363 0.38Locus BLIA AmaLgam BLUiR BRTracer BugLocator 0.00 0.25 0.50 0.75 1.00 Distribution of MAP values of all subjects for each techniques 0.455 0.501 0.43 0.516 0.497 0.506Locus BLIA AmaLgam BLUiR BRTracer BugLocator 0.00 0.25 0.50 0.75 1.00 Distribution of MRR values of all subjects for each techniques Baseline Performance !30

31. ●● ●● 0.359 0.35 0.359 0.365 0.363 0.38Locus BLIA AmaLgam BLUiR BRTracer BugLocator 0.00 0.25 0.50 0.75 1.00 Distribution of MAP values of all subjects for each techniques 0.455 0.501 0.43 0.516 0.497 0.506Locus BLIA AmaLgam BLUiR BRTracer BugLocator 0.00 0.25 0.50 0.75 1.00 Distribution of MRR values of all subjects for each techniques Baseline Performance Bug localization still has much room for improvement. !31

32. Technique Old Subjects New Subjects MAP MRR MAP MRR BugLocator 0.2692 0.3985 ↗0.3052 ↗0.4223 BRTracer 0.2645 0.3664 ↗0.3330 ↗0.4690 BLUiR 0.3102 0.4556 0.2881 0.3869 AmaLgam 0.2950 0.4072 0.2906 0.3899 BLIA 0.2935 0.4242 ↗0.3014 0.4155 Locus 0.2641 0.3399 ↗0.3289 ↗0.4430 Single version matching Test ﬁles included Summary of MAP/MRR of IRBL techniques !32 Conﬁguration RQ1:   The use of old vs. new subjects

33. Summary of MAP/MRR of IRBL techniques Not over-fitted to old subjects Technique Old Subjects New Subjects MAP MRR MAP MRR BugLocator 0.2692 0.3985 ↗0.3052 ↗0.4223 BRTracer 0.2645 0.3664 ↗0.3330 ↗0.4690 BLUiR 0.3102 0.4556 0.2881 0.3869 AmaLgam 0.2950 0.4072 0.2906 0.3899 BLIA 0.2935 0.4242 ↗0.3014 0.4155 Locus 0.2641 0.3399 ↗0.3289 ↗0.4430 !33 Single version matching Test files included Configuration RQ1:   The use of old vs. new subjects

34. !34 Summary of MAP/MRR of IRBL techniques Technique Single Version Multiple Version MAP MRR MAP MRR BugLocator 0.3052 0.4223 ↗0.3713 ↗0.5075 BRTracer 0.3330 0.4690 ↗0.3992 ↗0.5526 BLUiR 0.2881 0.3869 ↗0.3623 ↗0.4802 AmaLgam 0.2906 0.3899 ↗0.3657 ↗0.4840 BLIA 0.3014 0.4155 ↗0.3777 ↗0.5124 Locus 0.3289 0.4430 ↗0.4217 ↗0.5514 New subjects Test ﬁles included Conﬁguration RQ2:   The importance of version matching

35. New subjects Test ﬁles included Summary of MAP/MRR of IRBL techniques The evaluation/execution of IRBL techniques should apply multiple version matching !35 Technique Single Version Multiple Version MAP MRR MAP MRR BugLocator 0.3052 0.4223 ↗0.3713 ↗0.5075 BRTracer 0.3330 0.4690 ↗0.3992 ↗0.5526 BLUiR 0.2881 0.3869 ↗0.3623 ↗0.4802 AmaLgam 0.2906 0.3899 ↗0.3657 ↗0.4840 BLIA 0.3014 0.4155 ↗0.3777 ↗0.5124 Locus 0.3289 0.4430 ↗0.4217 ↗0.5514 Conﬁguration RQ2:   The importance of version matching

36. ConﬁgurationSummary of MAP/MRR of IRBL techniques !36 Multiple version matching New subjects RQ3:   The impact of test ﬁle inclusion Technique Test files excluded Test files included MAP MRR MAP MRR BugLocator 0.3811 0.4647 0.3713 ↗0.5075 BRTracer 0.4141 0.5090 0.3992 ↗0.5526 BLUiR 0.3603 0.4385 ↗0.3623 ↗0.4802 AmaLgam 0.3633 0.4420 0.3657 ↗0.4840 BLIA 0.3902 0.4728 ↗0.3777 ↗0.5124 Locus 0.4146 0.5002 ↗0.4217 ↗0.5514

37. Summary of MAP/MRR of IRBL techniques Technique Test files excluded Test files included MAP MRR MAP MRR BugLocator 0.3811 0.4647 0.3713 ↗0.5075 BRTracer 0.4141 0.5090 0.3992 ↗0.5526 BLUiR 0.3603 0.4385 ↗0.3623 ↗0.4802 AmaLgam 0.3633 0.4420 0.3657 ↗0.4840 BLIA 0.3902 0.4728 ↗0.3777 ↗0.5124 Locus 0.4146 0.5002 ↗0.4217 ↗0.5514 !37 Including test files does not bring bias or noise Configuration Multiple version matching New subjects RQ3:   The impact of test file inclusion

38. RQ4:   Leveraging duplicate bugs reports !38 Technique Master Duplicate Merged (Master+Duplicate) MAP MRR MAP MRR MAP MRR BugLocator 0.3503 0.5051 0.3259 0.4667 0.3502 ↗0.5249 BRTracer 0.3852 0.5508 0.3776 0.5430 0.3787 ↗0.5692 BLUiR 0.3159 0.4540 0.2804 0.4192 ↗0.3325 ↗0.4728 AmaLgam 0.3202 0.4581 0.2829 0.4223 ↗0.3327 ↗0.4725 BLIA 0.3518 0.4915 0.3231 0.4537 ↗0.3577 ↗0.5041 Locus 0.2915 0.4707 0.2871 ↗0.4724 ↗0.3042 ↗0.5021 Summary of MAP/MRR of IRBL techniques

39. !39 Summary of MAP/MRR of IRBL techniques RQ4:   Leveraging duplicate bugs reports Technique Master Duplicate Merged (Master+Duplicate) MAP MRR MAP MRR MAP MRR BugLocator 0.3503 0.5051 0.3259 0.4667 0.3502 ↗0.5249 BRTracer 0.3852 0.5508 0.3776 0.5430 0.3787 ↗0.5692 BLUiR 0.3159 0.4540 0.2804 0.4192 ↗0.3325 ↗0.4728 AmaLgam 0.3202 0.4581 0.2829 0.4223 ↗0.3327 ↗0.4725 BLIA 0.3518 0.4915 0.3231 0.4537 ↗0.3577 ↗0.5041 Locus 0.2915 0.4707 0.2871 ↗0.4724 ↗0.3042 ↗0.5021 Duplicate reports are complement master bug reports and guarantee a minimum level of performance

40. Summary !40

41. !41 Dataset Available https://github.com/exatoa/Bench4BL

42. Bug Linking !42

43. Bug-Code Linking Bug Report CAMEL-12558: Transacted and Policy should not have outputs M main/java/org/apache/camel/model/PolicyDeﬁnition.java M main/java/org/apache/camel/model/TransactedDeﬁnition.java A test/java/org/apache/camel/catalog/CamelCatalog.java A main/java/org/apache/camel/tools/apt/CoreEipAnnotationPrint.java Added camel-web3j Spring-boot test A test/java/org/apache/camel/itest/springboot/CamelWeb3jTest.java    Update GoogleBigQueryProducer.java M main/java/org/apache/camel/component/GoogleBigQueryProducer.java Code Repository Commit Log !43

44. Bug-Code Linking Bug Report CAMEL-12558: Transacted and Policy should not have outputs M main/java/org/apache/camel/model/PolicyDeﬁnition.java M main/java/org/apache/camel/model/TransactedDeﬁnition.java A test/java/org/apache/camel/catalog/CamelCatalog.java A main/java/org/apache/camel/tools/apt/CoreEipAnnotationPrint.java Added camel-web3j Spring-boot test A test/java/org/apache/camel/itest/springboot/CamelWeb3jTest.java    Update GoogleBigQueryProducer.java M main/java/org/apache/camel/component/GoogleBigQueryProducer.java Code Repository Commit Log !44

45. Bug Oracle ……….. …. ….. …..…. ……..  …. .. main/java/org/apache/camel/model/PolicyDeﬁnition.java main/java/org/apache/camel/model/TransactedDeﬁnition.java test/java/org/apache/camel/catalog/CamelCatalog.java main/java/org/apache/camel/tools/apt/CoreEipAnnotationPrint.java ……….. …. ….. …..…. ……..  …. .. main/java/org/apache/camel/GoogleBigQueryProducer.java ……….. …. ….. …..…. ……..  …. .. main/java/org/apache/camel/component/StringConcatenator.java Bug Report 1 Bug Report 2 Bug Report 3 ……. !45

46. Version Matching !46

47. Version Matching Strategy Single version Matching !47 Previous Techniques

48. Version Matching Strategy Single version Matching Multiple version Matching !48 Previous Techniques

49. Version Matching Approach !49

50. Version Matching Approach Selecting earliest version !50

51. Test Case Inclusion !51

52. Test File Inclusion CAMEL-12558: Transacted and Policy should not have outputs M main/java/org/apache/camel/model/PolicyDeﬁnition.java M main/java/org/apache/camel/model/TransactedDeﬁnition.java A test/java/org/apache/camel/catalog/CamelCatalog.java A main/java/org/apache/camel/tools/apt/CoreEipAnnotationPrint.java Added camel-web3j Spring-boot test A test/java/org/apache/camel/itest/springboot/CamelWeb3jTest.java    Update GoogleBigQueryProducer.java M main/java/org/apache/camel/component/GoogleBigQueryProducer.java Code Repository Commit LogBugLocator BLIA Locus AmaLgam BRTracer BLUiR !52

53. Test File Inclusion CAMEL-12558: Transacted and Policy should not have outputs M main/java/org/apache/camel/model/PolicyDefinition.java M main/java/org/apache/camel/model/TransactedDefinition.java A test/java/org/apache/camel/catalog/CamelCatalog.java A main/java/org/apache/camel/tools/apt/CoreEipAnnotationPrint.java Added camel-web3j Spring-boot test A test/java/org/apache/camel/itest/springboot/CamelWeb3jTest.java    Update GoogleBigQueryProducer.java M main/java/org/apache/camel/component/GoogleBigQueryProducer.java Code Repository Commit LogBugLocator BLIA Locus AmaLgam BRTracer BLUiR We remove   including “test” or “Test” in a path or filename !53

54. Duplicate Report !54

55. Duplicate Bug Reports 46  Projects New Subjects 690   Major Versions 9,459   Bug Reports ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. 807   Duplicate Reports 5  Projects 5   Major Versions 558   Bug Reports ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. ……….. …. ….. …..…. ……..  …. .. 136   Duplicate Reports Old Subjects !55

56. Duplicate Bug Reports !56

57. Duplicate Bug Reports MATH-760 MATH-1192 MATH-2022 MATH-760 MATH-1192 MATH-760 MATH-2022 !57

Bench4BL: Reproducibility Study on the Performance of IR-Based Bug Localization

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