Slides used during the workshop at the JFall conference.

1. 1 • 8-November-23

2. 2 • 8-November-23
Picnic and its code quality
1
Introduction of Error Prone and Refaster
2
Workshop 1 - Initial setup
3
Workshop 2 - Refaster
4
Agenda
Workshop 3 - Error Prone
5
Using Error Prone in practice!
6

3. 3 • 8-November-23
Picnic

4. 4 • 8-November-23
Code quality

5. 5 • 8-November-23
Excellent code quality
Good architecture
Review process
Bugs and uniformity
Automation

6. 6 • 8-November-23
Parkinson's law of triviality

7. 7 • 8-November-23
Code reviews and discussions

8. 8 • 8-November-23
Tools
Google/google-java-format
Reformats Java source code to comply
with Google Java Style.
checkstyle/checkstyle
Helps programmers write Java code
that adheres to a coding standard.
spotbugs/spotbugs
A tool for static analysis to look
for bugs in Java code.
SonarSource/sonarqube
Continuous Inspection.

9. 9 • 8-November-23
Picnic and its code quality
1
Introduction of Error Prone and Refaster
2
Workshop 1 - Initial setup
3
Workshop 2 - Refaster
4
Agenda
Workshop 3 - Error Prone
5
Using Error Prone in practice!
6

10. 10 • 8-November-23
Open-source static analysis
Compiler plugin
Powerful
500+ Error Prone checks
Complex
Error Prone
Google/error-prone
Catch common Java mistakes
as compile-time errors

11. 11 • 8-November-23
Refaster
Define refactorings with templates.
becomes

12. 12 • 8-November-23
Demo
Let’s demonstrate!
https://github.com/rickie/error-prone-demo

13. 13 • 8-November-23
Maven profile 1
https://errorprone.info/docs/flags

14. 14 • 8-November-23
Maven profile 2

15. 15 • 8-November-23
Demo
Let’s demonstrate!
https://github.com/rickie/error-prone-demo

16. 16 • 8-November-23
Bug patterns
https://errorprone.info/bugpatterns

17. 17 • 8-November-23
Error Prone as superpower

18. 18 • 8-November-23
Error Prone as superpower
Input:
Output:

19. 19 • 8-November-23
Workshop planning
1. Setting up the project
2. Refaster rules
3. Error Prone checks

20. 20 • 8-November-23
Picnic and its code quality
1
Introduction of Error Prone and Refaster
2
Workshop 1 - Initial setup
3
Workshop 2 - Refaster
4
Agenda
Workshop 3 - Error Prone
5
Using Error Prone in practice!
6

21. 21 • 8-November-23
At Picnic we take it one step further!

22. 22 • 8-November-23
Picnic open-sourced: Error Prone Support!
800+ Refaster rules
40+ Error Prone bug checks
https://error-prone.picnic.tech

23. 23 • 8-November-23
Error Prone BugPattern

24. 24 • 8-November-23
Error Prone BugPattern

25. 25 • 8-November-23
Picnic’s Error Prone Support
Run Refaster rules from classpath
Test support for Refaster rules
Improved reporting of Refaster rules
Documentation website
https://error-prone.picnic.tech

26. 26 • 8-November-23
Error Prone Support website
https://error-prone.picnic.tech

27. 27 • 8-November-23
Let’s start with the setup!
PicnicSupermarket
error-prone-support
Error Prone extensions:
extra bug checkers and a large battery of
Refaster rules.
branch: workshop

28. 28 • 8-November-23
Picnic and its code quality
1
Introduction of Error Prone and Refaster
2
Workshop 1 - Initial setup
3
Workshop 2 - Refaster
4
Agenda
Workshop 3 - Error Prone
5
Using Error Prone in practice!
6

29. 29 • 8-November-23
Deep dive Refaster
- Background information
- Goals
- How does Refaster work?
- Advanced features

30. 30 • 8-November-23
Refaster
- 2015 - Louis Wasserman (source)
- Two tools
- Closed source

31. 31 • 8-November-23
Refaster rules availability

32. 32 • 8-November-23
Deep dive Refaster
Goals of Refaster (source):
- Scalability
- Expressiveness
- Usability
When to use Refaster? (docs)
- Method A to method B.
- Migrate a fluent sequence of method invocations to some other
pattern.
- Migrate a sequence of consecutive statements to an alternative.

33. 33 • 8-November-23
Running Refaster

34. 34 • 8-November-23
Running Refaster - The Picnic Way
Link to an example configuration in Error Prone Support

35. 35 • 8-November-23
Running Refaster - The Picnic Way
Refaster runner - `pom.xml` in Error Prone Support

36. 36 • 8-November-23
Refaster @ Picnic

37. 37 • 8-November-23
Refaster @ Picnic

38. 38 • 8-November-23
Advanced Refaster features

39. 39 • 8-November-23
Multiple
`@BeforeTemplate`s

40. 40 • 8-November-23
Refaster#anyOf

41. 41 • 8-November-23
@AlsoNegation

42. 42 • 8-November-23
Import policies
IMPORT_TOP_LEVEL
IMPORT_CLASS_DIRECTLY
STATIC_IMPORT_ALWAYS

43. 43 • 8-November-23
Block Template

44. 44 • 8-November-23
@Placeholder

45. 45 • 8-November-23
Argument types

46. 46 • 8-November-23
Workshop part 2 - Refaster
30 minutes
Workshop README
Live demo!
Tip: use the slides
Once you are done: commit + push

47. 47 • 8-November-23
Let’s inspect the changes!

48. 48 • 8-November-23
Picnic and its code quality
1
Introduction of Error Prone and Refaster
2
Workshop 1 - Initial setup
3
Workshop 2 - Refaster
4
Agenda
Workshop 3 - Error Prone
5
Using Error Prone in practice!
6

49. 49 • 8-November-23
Deep dive Error Prone
- Background
- How to write a BugPattern?
- Automatically fixing code
- How to test a BugPattern?

50. 50 • 8-November-23
Error Prone background
- 2012 - Edward Aftandilian
- Code review and unit testing
- Subclass JavaCompiler
- CompilationUnit level
Source: Error Prone paper
OpenRewrite docs

51. 51 • 8-November-23
Rules for an Error Prone check
1. The bug should be easy to understand.
2. The fix should be easy to make.
3. No false positives.
4. The bug should represent a correctness issue.
5. The bug should occur with a small but noticeable frequency.
https://errorprone.info/docs/criteria

52. 52 • 8-November-23
How does Error Prone work?
Java code Abstract Syntax Tree Tree Node

53. 53 • 8-November-23
Abstract Syntax Tree

54. 54 • 8-November-23
Abstract Syntax Tree

55. 55 • 8-November-23
Creating a BugChecker

56. 56 • 8-November-23
Automatically fixing code!
Flagging vs. Fixing

57. 57 • 8-November-23
Automatically fixing code!

58. 58 • 8-November-23
Testing our BugChecker

59. 59 • 8-November-23
Testing our
BugChecker

60. 60 • 8-November-23
Refaster vs. Error Prone
Easy: work with
concrete syntax
Complex: AST
manipulation code
Limited
expressiveness
Full AST available
Refactoring only Also flags
without suggestions

61. 61 • 8-November-23
Workshop part 3 - Error Prone
45 minutes
Live demo
5 assignments
Workshop README

62. 62 • 8-November-23
Picnic and its code quality
1
Introduction of Error Prone and Refaster
2
Workshop 1 - Initial setup
3
Workshop 2 - Refaster
4
Agenda
Workshop 3 - Error Prone
5
Using Error Prone in practice!
6

63. 63 • 8-November-23
Error Prone @ Picnic
Common configuration
./patch.sh
Continuous Integration

64. 64 • 8-November-23
Applying Error Prone Support @ Picnic
Introducing:
- all Refaster rules
- all Error Prone checks
Approach
Perspective
https://error-prone.picnic.tech

65. 65 • 8-November-23
Applying Error Prone Support @ Picnic
60+ PRs spread over 40+ Java repositories
33.665 insertions (+) 31.281 deletions (-)

66. 66 • 8-November-23
Applying Error Prone Support @ Picnic

67. 67 • 8-November-23
Applying Error Prone Support @ Picnic

68. 68 • 8-November-23
Current state of Error Prone Support
People contributing ideas (from reviews)
40+ contributors
Stickers
Contributions?
Adoption

69. 69 • 8-November-23
In summary
Two perspectives:
- Happy developers!
- Platform team or configuration
maintainers.

70. Automatically fix
One bug at a time
join.picnic.app
blog.picnic.nl

71. 71 • 8-November-23
Unsure about next steps?
Feel free to reach out!
- https://error-prone.picnic.tech
- https://github.com/rickie/error-prone-demo - Demo code
Stephan Schroevers - stephan.schroevers@teampicnic.com
GitHub: https://github.com/Stephan202
Rick Ossendrijver - rick.ossendrijver@teampicnic.com
GitHub: https://github.com/rickie
Twitter: rick_ossies
We’re open to PRs ;)