Error Prone is a powerful tool for detecting and preventing bugs and anti-patterns in Java codebases. As a compiler plugin, it is capable of automatically suggesting and applying fixes at scale. For years, Picnic has leveraged the capabilities of Error Prone to streamline our development process through large-scale automated refactorings across our entire Java codebase. This approach not only resolves bugs once and for all, but also leads to a more consistent and high-quality codebase. In this talk, we will provide a comprehensive demonstration of Error Prone's capabilities, as well as offer practical guidance on how to set up the tool for your own development team. Additionally, we will share our own experiences and learnings from Picnic's journey of using Error Prone, including the process of creating and enabling our own set of custom rules from our open-sourced Error Prone Support repository.

1. Rick Ossendrijver
Automating away bugs
with Error Prone in practice

2. 2 • 23-Feb-23
Picnic and its processes
1
Introduce Error Prone
2
Using Error Prone in practice!
3
Error Prone @ Picnic
4
Agenda

3. 3 • 23-Feb-23
Mobile
+
Picnic’s Online Groceries Model
Groceries
+
Home Picnic
Lowest price
On-time
=
+ +

4. 4 • 14-Feb-23
7
Years
300
Engineers
3M
Customers
5M
Lines of code
Our numbers

5. 5 • 23-Feb-23
Code quality

6. 6 • 23-Feb-23
Excellent code quality
Good architecture
Bugs and uniformity
Review process
Automation

7. 7 • 23-Feb-23
Code reviews and discussions

8. 8 • 23-Feb-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 • 23-Feb-23
Picnic and its processes
1
Introduce Error Prone
2
Using Error Prone in practice!
3
Error Prone @ Picnic
4
Agenda

10. 10 • 23-Feb-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 • 23-Feb-23
Refaster
Define refactorings with templates.
becomes

12. 12 • 23-Feb-23
Demo
Let’s demonstrate!

13. 13 • 23-Feb-23
Maven profile 1

14. 14 • 23-Feb-23
Maven profile 2

15. 15 • 23-Feb-23
Demo
Let’s demonstrate!

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

17. 17 • 23-Feb-23
Error Prone as superpower

18. 18 • 23-Feb-23
Error Prone as superpower
What would that look like?
https://github.com/rickie/guava/

19. 19 • 23-Feb-23
Picnic and its processes
1
Introduce Error Prone
2
Using Error Prone in practice!
3
Error Prone @ Picnic
4
Agenda

20. 20 • 23-Feb-23
Roadmap to Enable Error Prone
Level 1:
Disable everything
Level 2:
Selectively turn on a
few ERROR checks
Level 3:
Turn on all default
ERROR checks

21. 21 • 23-Feb-23
Demo: introducing Error Prone in practice!
Let’s demonstrate!

22. 22 • 23-Feb-23
Roadmap to Enable Error Prone
Level 1:
Disable everything
Level 2:
Selectively turn on a
few ERROR checks
Level 3:
Turn on all default
ERROR checks

23. 23 • 23-Feb-23
Picnic and its processes
1
Introduce Error Prone
2
Using Error Prone in practice!
3
Error Prone @ Picnic
4
Agenda

24. 24 • 23-Feb-23
Error Prone @ Picnic
Common configuration
./patch.sh
Continuous Integration

25. 25 • 23-Feb-23
Now, we want more…

26. 26 • 23-Feb-23
Picnic open-sourced: Error Prone Support!
700+ Refaster rules
40+ Error Prone bug checks
https://error-prone.picnic.tech

27. 27 • 23-Feb-23
Picnic’s Error Prone Support
Run Refaster rules from classpath
Test support for Refaster rules
Improved reporting on Refaster rules
Documentation website
https://error-prone.picnic.tech

28. 28 • 23-Feb-23
Error Prone Support website
https://error-prone.picnic.tech

29. 29 • 23-Feb-23
Applying Error Prone Support @ Picnic
Introducing:
- all Refaster rules
- all Error Prone checks
Approach
Perspective
https://error-prone.picnic.tech

30. 30 • 23-Feb-23
Applying Error Prone Support @ Picnic
60+ PRs spread over 40+ Java repositories
33.665 insertions (+) 31.281 deletions (-)

31. 31 • 23-Feb-23
Applying Error Prone Support @ Picnic

32. 32 • 23-Feb-23
Applying Error Prone Support @ Picnic

33. 33 • 23-Feb-23
Current state of Error Prone Support
People contributing ideas (from reviews)
30+ contributors
Stickers
Adoption
GitHub Issues

34. 34 • 23-Feb-23
Conclusion
Two perspectives:
- Happy developers!
- Platform team or configuration
maintainers.

35. 35 • 23-Feb-23
Unsure about next steps?
Feel free to reach out!
- https://errorprone.info
- https://error-prone.picnic.tech
Special thanks to:
Stephan Schroevers - stephan.schroevers@teampicnic.com
https://github.com/Stephan202
Contact details:
Rick Ossendrijver - rick.ossendrijver@teampicnic.com
https://github.com/rickie