Code Analysis Via Version Control History

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1 Code Analysis Via Version Control History Justin Mclean Class Software Blog:

2 Who am I? Freelance Developer Programming for 25 years Apache Flex PMC, Incubator PMC, Apache member and mentor for several incubator projects Run IoT meetup in Sydney Australia

3 In the last 40 years we have written billions of lines of code that will keep programmers employed for trillions of man hours in the next few thousand years to clean up this mess we ve made. Joe Armstrong

4 Your Code as a Crime Scene

5 You Write Code? 40-80% of all code is maintenance Goal is to understand existing code This is difficult, time consuming and expensive Perhaps more so with agile methodologies? How can we fix this?

6 Detecting Issues With Code Code reviews Pair programming Unit tests Continuous integration Static code analysis Complexity metrics

7 Scalability What about legacy code? What about large code bases? How do you decide what to work on? How to work out where the bugs are? What bugs are actually important?

8 Code Visualisation Can you visually represent code to get a better understanding of what s going on? Code City Make a city of each class arranged by packages in city blocks Height is number of methods, colour coded by no of lines and area by no of terms

9 Code City

10 Code City Limitations Supports only a few common languages Shows complexity (large buildings) but no real indication of where to possibly spend effort Existing hotspots may be stable

11 Version Control History Version control history contains a lot of useful information that we mostly ignore. Information like: Who changed what lines when How much and how often things change Can we aggregate information to tell us something useful?

12 Why Code Changes New functionality Fixing bugs Refactoring Poor understanding of the problem Change frequency == proxy for effort Code that changes in the past is likely to change again in the future

13 Effort and Complexity Change frequency / effort is not the whole story Configuration files changes frequently Overlaps in effort and complexity gives better possible hotspots

14 Code Hotspots Hotspots are places where complex code changes frequently Frequent changes to complex code usually indicate poor quality or buggy code Surprisingly simple complexity measures perform just as well as more complex measures

15 What use are Hotspots? Take cognitive biases out of the equation Where you bugs are likely to be Point out areas for code reviews refactoring extra testing documentation

16 Code Maat Performs various analysis on version control history Produces simple csv text files Supports parsing git, svn, mercurial version control systems Open source (GPL licensed)

17 Producing HotSpot Data Clone repo Work out time period Generate log summary data Generate change frequencies Generate code complexity metrics Combine to find hotspots

18 Apache Flex Project Large code base 25,000 files, 5 million loc or about 20 million loc including tests Mix of many file types and languages MXML, ActionScript, Java, XML files Two distinct phases, before and after donation Mature code base

19 Adobe Flex SDK Summary statistic,value number-of-commits,30090 number-of-entities,4672 number-of-entities-changed,34916 number-of-authors,18

20 Apache Flex SDK Summary statistic,value number-of-commits,3096 number-of-entities,51550 number-of-entities-changed,82508 number-of-authors,57

21 Complexity LOC is a terrible complexity measure, but turns out it s just as bad as most others It s fast and simple Language agnostic (mostly) CLOC

22 Apache Flex SDK Revisions module,revisions,code build.xml,142,1432 frameworks/build.xml,60,432 mustella/jenkins.sh,50,167 mustella/build.xml,44,1988 modules/downloads.xml,39,388 ide/checkallplayerglobals.sh,38,87 frameworks/projects/mobiletheme/defaults.css,35,1568 frameworks/projects/framework/src/mx/collections/listcollectionview.as,33,1442 frameworks/downloads.xml,31,257 installer.xml,29,821 frameworks/projects/spark/build.xml,28,231 frameworks/projects/advancedgrids/src/mx/controls/advanceddatagridbaseex.as,28,4781

23 Apache Flex SDK Last Year module,revisions,code frameworks/projects/framework/src/mx/collections/listcollectionview.as,13,1442 build.xml,12,1432 frameworks/projects/mobiletheme/defaults.css,10,1568 frameworks/projects/spark/src/spark/collections/sort.as,9,82 frameworks/projects/framework/src/mx/collections/sort.as,9,405 frameworks/projects/spark/src/spark/components/datagrid.as,8,2881 frameworks/projects/advancedgrids/src/mx/collections/hierarchicalcollectionviewcursor.as,7,830 frameworks/build.xml,7,432 frameworks/projects/framework/src/mx/collections/sortfield.as,7,356 frameworks/projects/framework/src/mx/utils/objectutil.as,7,791 frameworks/projects/framework/src/mx/collections/complexsortfield.as,7,31 frameworks/projects/framework/src/mx/collections/arraylist.as,7,356 frameworks/projects/spark/src/spark/components/callout.as,6,864 modules/downloads.xml,6,388

24 Hot Spot Confirmation Build and install files Mobile theme ListCollections DataGrid and AdvancedDataGrid DateField

25 Recent Hot Spots Past year: List Collections and Sorting Mobile Themes DataGrid and AdvancedDataGrid Build Scripts Experimental components

26 Hot Spot Limitations Just numbers so may need to normalise Time period may be hard to get right (hotspots move above over time) Some impact by individual commit styles May be some false positives Just a guide, but still a very useful one

27 Visualise Hot Spots Hard to understand a large amount of information Classes are nested in packages and we have complexity and change frequency / effort Circle packing works well. Circle size is loc, colour by change frequency. D3.js easy to use / can display easily Need CSV -> JSON conversion

28 Apache Flex SDK

29 Apache Flex SDK

30 Apache Flex SDK

31 Apache Flex SDK

32 Hotspot Analysis Hotspots are small proportion of all code Configuration files vs complex application logic Can have false positives

33 Hotspot Analysis 3rd party modules and compiler stable Experimental area is an unknown Data grids have been and are still an issue Collections classes being heavily worked on

34 Apache FlexJS

35 Hotspot Analysis Doesn t seem to be a lot of tests Large no of hotspots means lot of change happening XML and Flat theme likely to have bugs UIBase good candidate for refactoring

36 Apache Falcon

37 Hotspot Analysis Reasonably stable in most areas Flex JS / AS / Goog emitters prime candidate for refactoring

38 Apache Mynewt

39 Hotspot Analysis BLE area lots going on Changes in core around tasks, semaphores, scheduling, time, buffers Tests not changing as fast as other code

40 Complexity (again) LOC is OK as a bad measure but is there something a little better? Whitespace indentation! Easy to calculate (Mostly) language independent

41 DataGrid.as complexity CLOC shows 50/50 split between code and comments with 2800 lines of actual code. May be good idea to remove comments? DataGrid.as whitespace n,total,mean,sd,max 5860,9244,1.58,1.21,13 Mean is low, sd is low, but max is way too high We have a real hotspot

42 rev,n,total,mean,sd f52eb16,5608,8816,1.57,1.23 0c4290c,5609,8816,1.57, a8,5644,8856,1.57,1.23 fa2108b,5644,8856,1.57,1.23 abc381b,5644,8856,1.57, cdd7,5791,9061,1.56,1.22 5e6e5c3,5791,9061,1.56, da8,5791,9061,1.56,1.22 ec1ac28,5810,9090,1.56, b68de,5839,9124,1.56,1.22 b1d0359,5855,9164,1.57,1.22 1bef097,5851,9158,1.57,1.22 3e752d9,5854,9165,1.57,1.22 6c53962,5857,9172,1.57,1.22 c47f9f9,5855,9169,1.57,1.22 bb600fd,5855,9169,1.57, f8757,5853,9230,1.58,1.21 3a1769b,5860,9247,1.58, c20,5860,9244,1.58,1.21 Complexity Trend

43 UIBase Complexity Trend

44 Temporal Coupling File that need to change at the same time Causes: Copy paste Inadequate encapsulation Anti-pattern sometimes referred to as shotgun surgery

45 Detect Temporal Coupling Results are a bit noisy - may need to filter frameworks/projects/framework/src/mx/states/additems.as,frameworks/projects/mx/src/mx/core/container.as,83,6 frameworks/projects/framework/src/mx/states/additems.as,frameworks/projects/spark/src/spark/components/skinnablecontainer.as,83,6 frameworks/projects/mx/src/mx/core/container.as,frameworks/projects/spark/src/spark/components/group.as,76,7 frameworks/projects/mx/src/mx/containers/viewstack.as,frameworks/projects/spark/src/spark/components/skinnablecontainer.as,76,7 frameworks/projects/framework/src/mx/states/additems.as,frameworks/projects/mx/src/mx/containers/viewstack.as,76,7 frameworks/projects/mx/src/mx/containers/viewstack.as,frameworks/projects/mx/src/mx/core/container.as,76,7 frameworks/projects/spark/src/spark/components/group.as,frameworks/projects/spark/src/spark/components/skinnablecontainer.as,76,7 frameworks/projects/mx/src/mx/containers/viewstack.as,frameworks/projects/spark/src/spark/components/group.as,71,7 frameworks/projects/framework/src/mx/core/uicomponent.as,frameworks/projects/spark/src/spark/components/skinnablecontainer.as,63,10 frameworks/projects/framework/src/mx/core/uicomponent.as,frameworks/projects/framework/src/mx/states/additems.as,63,10 frameworks/projects/framework/src/mx/core/uicomponent.as,frameworks/projects/spark/src/spark/components/group.as,60,10

46 Apache Mynewt

47 Apache Flex SDK

48 Flex JS

49 Flex Falcon

50 Mynewt

51 Knowledge Map Generate ownership of files Multiple owners per file imply more potential bugs Knowledge maps - who know most about which files

52 Apache Flex SDK

53 Apache Flex SDK

54 What we have learnt Lot of useful information in your version control history waiting to be found out Technique scales easily to (very) large code bases Keep data formats simple Simple measures of effort and complexity are often as good as complex ones Can use version control history to find the areas that need attention in your code base

55 Links Code as a crime scene Code City CLOC Code Maat

56 Questions? Ask now, see me after the session, follow me on or me at Slides can be found at conference site.