1. Rename Local Variable Refactoring Instances
Detection of
Rename Local Variable Refactoring Instances in
Commit History
Matin Mansouri
Advisor: Dr. Nikolaos Tsantalis
Date department

2. Refactoring

3. The process of changing a software system in such a way that it does not alter the external behavior of the code, yet improves its internal structure
Say refactoring is a very common activity
A study at Microsoft
revealed that 22% of developers initiate refactorings because of poor readability, and 11% because of
poor maintainability [KZN14]. Moreover, 43% of developers mentioned that they actually perceived
better code readability, and around 30% perceived improved code maintainability after refactoring.
According to this study, developers spend about 10% of their time in each month working on
refactoring

4. A Frequent Activity
Refactoring is done regularly [Murphy-Hill et al, TSE2012]
Overall, about 16% of all the changes [Xing et al, ICSM2006]
Developers consider refactoring an integral part of their programming [Ge et al, ICSE2014]
10% of development time is spent on refactoring [Kim et-al, TSE2014]

5. A Beneficial Activity Microsoft study [Kim et-al, TSE2014]:
Benefits observed from refactoring
30% improve maintainability
43% improved readability
27% add feature easier, improve extensibility, and fewer bugs
When refactoring is performed
22% because of poor readability
13% code duplication
11% because of poor maintainability
Maitainability yani chi tu paper

6. However… Refactorings slow down code review [Ge et al, VLHCC2017]
Global refactorings can easily lead to merge conflicts [Dig et al, TSE2008]
80% of the breaking changes to the APIs are because of refactorings [Dig et al, ICSM2005]
Refactorings affect negatively the process of accurately locating bug-introducing changes [Costa et al, TSE2016]

7. But these can be mitigated if we could identify the applied refactorings

8. Refactoring Detection to the Rescue
Refactorings slow down code review [Ge et al, VLHCC2017]
Refactoring-aware code review
 Global changes can easily lead to merge conflicts [Dig et al, TSE2008]
Refactoring-aware code merging
 80% of the breaking changes to the APIs are because of refactorings [Dig et al, ICSM2005]
Refactoring-aware client adaptation
1. Of the 165 developers survey

9. Refactoring Detection to the Rescue
Refactorings affect negatively the process of accurately locating bug-introducing changes [Costa et al, TSE2016]
Improving the accuracy of SZZ algorithm
In addition
Empirical studies showed contradicting results regarding the refactoring effect on the code [Soares et al, JSS2013]
Precise tool for accurate studies
1. Of the 165 developers survey

10. Refactoring Detection:
The process of identifying a set of refactorings that have been applied between two revisions of a software system

11. Refactoring Detection Approaches
RefactoringCrawler [Dig et al,  ECOOP2006]
Ref-Finder [Prete et al, ICSM2010]
RefDiff [Silva et al, MSR2017]
RefactoringMiner [Tsantalis et al, ICSE2018]
Renaming detection [Malpohl et al, ASE2000]
REPENT [Arnaoudova et-al, TSE2014]

12. However… These approaches are incomplete
Not all refactoring types are supported
E.g., Rename Local Variable refactoring

13. Why Rename Local Variable?
Rename refactoring is the most applied refactoring (up to 74%) [Murphy-Hill et al, TSE2012]
Rename local variable is the second most applied rename refactoring (~25%) [Arnaoudova et al, TSE2014]
21% developers do the rename refactoring everyday [Arnaoudova et al, TSE2014]
As important as other refactorings
Slide add before this for naming refactoring tool

14. Refactoring Detection Approaches
RefactoringCrawler [Dig et al,  ECOOP2006]
Ref-Finder [Prete et al, ICSM2010]
RefDiff [Silva et al, MSR2017]
RefactoringMiner [Tsantalis et al, ICSE2018]
Renaming detection [Malpohl et al, ASE2000]
REPENT [Arnaoudova et-al, TSE2014]
No Support for Rename Local Variable
Not Available

15. Rename Local Variable Detection is Difficult
Extract/inline method
A) before
B) after

16. Rename Local Variable Detection is Difficult
Textual diff approach limitation
public void invoke(...) {
...
ClusterMessage imsg = manager.
requestCompleted(invalidIds[i]);
if (imsg != null)
cluster.send(imsg);
if (session != null)
id = session.getIdInternal();
if (id == null)
return
ClusterMessage msg = manager.requestCompleted(id);
if (msg == null) return;
cluster.send(msg); }
protected void sendSessionReplicationMessage(...) {
String id = session.getIdInternal();
if (id != null) {
ClusterMessage msg = manager.requestCompleted(id);
if (msg != null)
cluster.send(msg); }
protected void sendInvalidSessions(...) {
ClusterMessage imsg = manager.requestCompleted(invalidIds[i]);
if (imsg != null)
cluster.send(imsg);

17. Rename Local Variable Detection is Difficult
Merge and split variable

18. Approach

19. Approach RefactoringMiner for: Rename local variable detection rules
Statement matching
Support for other refactoring types (e.g., extract/inline/rename method)
Rename local variable detection rules
Statement matching post-processing

20. outMessage -> response
RefactoringMiner
Statement Matching:
public dnsMessage sendAXFR(dnsMessage inMessage) {
Socket s;
...
dnsMessage outMessage;
s.getOutputStream().write(out);
outMessage = new dnsMessage();
while (true) {
outMessage.addRecord(dns.ANSWER, r); }
return outMessage;
public dnsMessage sendAXFR(dnsMessage query) {
Socket s;
...
dnsMessage response;
s.getOutputStream().write(out);
response = new dnsMessage();
while (true) {
response.addRecord(dns.ANSWER, r); }
return response;
outMessage -> response

21. Rename Local Variable Rules
There exists a replacement r which replaces the local variable l in the old revision with l’ in the new revision
public dnsMessage sendAXFR(dnsMessage inMessage) {
Socket s;
...
dnsMessage outMessage;
s.getOutputStream().write(out);
outMessage = new dnsMessage();
while (true) {
outMessage.addRecord(dns.ANSWER, r); }
return outMessage;
public dnsMessage sendAXFR(dnsMessage query) {
Socket s;
...
dnsMessage response;
s.getOutputStream().write(out);
response = new dnsMessage();
while (true) {
response.addRecord(dns.ANSWER, r); }
return response;

22. Rename Local Variable Rules
l should belong to the declared local variables in ma and l’ should belong to the declared local variables in ma'
l should not exist in the new revision of the code, and l’ should not exist in the old revision of the code
public dnsMessage sendAXFR(dnsMessage inMessage) {
Socket s;
...
dnsMessage outMessage;
s.getOutputStream().write(out);
outMessage = new dnsMessage();
while (true) {
outMessage.addRecord(dns.ANSWER, r); }
return outMessage;
public dnsMessage sendAXFR(dnsMessage query) {
Socket s;
...
dnsMessage response;
s.getOutputStream().write(out);
response = new dnsMessage();
while (true) {
response.addRecord(dns.ANSWER, r); }
return response;

23. Rename Local Variable Rules
l should not appear in the body of the methods extracted from ma ,as detected by RefactoringMiner
A) before
B) after

24. Rename Local Variable Rules
A local variable cannot be renamed to two local variables
Similarly two local variables cannot be renamed to one local variable

25. Statement Matching Post-Processing
Introducing scope
public static void main(String args[]) {
if (args.get(0) == 0) {
String response = args.get(1);
saveError(response);
} else {
saveResponse(response); }
public static void main(String args[]) {
if (args.get(0) == 0) {
String errorMessage = args.get(1);
saveError(errorMessage);
} else {
String message = args.get(1);
saveResponse(message); }

26. RefactoringMiner Matches Statements in a Greedy Way

27. Statement Matching Post-Processing
Find an optimal match

28. Evaluation

29. Evaluation Research Questions:
RQ1: How accurate is our technique in detecting instances of Rename Local Variable refactorings?
RQ2: How does our technique perform compared to REPENT?
RQ3: What is the efficiency of our technique in terms of the time taken for detecting instances of Rename Local Variable refactorings?

30. Oracle Construction
We used existing oracle provided by [Arnaoudova et-al, TSE2014]
Software
Revisions Period
Files
Total File Revisions
KLOC
Detected
Validated
dnsjava
365
1,415
9-35
144 32
Tomcat
12,205
46,498
5-315
397
180

31. RefBenchmark

32. RefBenchmark Applications: Unify the results of different tools
Compute agreement using two or more tools
Evaluate the results of the tools against an oracle

33. Extended Oracle Using RefBenchmark RefactoringMiner REPENT Software
#Refactorings
Agreed TP FP
Tomcat
396
268 76 55 52 77
dnsjava
128 93 19 9 17 34
Total
524
361 95 64 69
111
There are three validated by repent we couldnt find dns
One agreed on FP
Dns 66 laleh , 20 davood + 32 repent = 110
Tomcat = repent lale 40 + davood 10 = 230

34. RQ1-Our Approach is Accurate
Software
#Refactorings TP FP FN
Recall
Precision
Tomcat
396
344 55 52
86.9%
86.2%
dnsjava
128
111 10 17
86.7%
91.7%
Total
524
455 65 69
86.8%
87.5%

35. RQ2-Comparison with REPENT
RefactoringMiner
REPENT
Software
#Refactorings
Recall
Precision
Tomcat
396
86.9%
86.2%
80.8%
80.6%
dnsjava
128
86.7%
91.7%
85.2%
75.7%
Total
524
86.8%
87.5%
81.8%
79.3%

36. RQ3-Execution Time (ms)
Distribution of excetion time fro each commit

37. Conclusion Provided a comprehensive rename local variable oracle
The oracle is extended by 96 refactoring instances
All detected instances are validated manually
Added Rename local variable detection to RefactoringMiner
Outperforms the state-of-the-art approach (REPENT)
Introduced a refactoring results agreement platform (RefBenchmark)