This document summarizes lessons learned from failures in backporting bug fixes to Ruby stable branches: - Don't backport performance improvements or fixes for imaginary use cases as they can introduce regressions. - Be careful backporting fixes related to parsing, constants/method search, and refinements as they are complex and prone to causing new bugs. - Some long-standing bugs may not need fixing if no real applications are affected. It's better to avoid regressions. - Consider an application's needs before backporting - don't backport fixes if no one requested or needs them. Be practical.

1. 2019-04-19
All bug-fixes are incompatibilities
nagachika @ RubyKaigi 2019

2. Important Notification about RubyGems.org
The attackers try to hijack your
account with compromised
password list.
Example: bootstrap-sass was
compromised by this attack. It was
injected the vulnerable RCE code.
We should prepare the multi-factor
authentication on RubyGems.org
for protecting from them.

3. ✤ @nagachika
✤ CRuby committer
✤ CRuby stable branch maintainer (2.5 → 2.6)
✤ ruby trunk changes
✤ Fukuoka.rb/TFUG Fukuoka
WHO AM I

4. ✤ @nagachika
✤ CRuby committer
✤ CRuby stable branch maintainer (2.5 → 2.6)
✤ ruby trunk changes
✤ Fukuoka.rb/TFUG Fukuoka
WHO AM I

5. “What’s the Ruby’s
stable branch maintenance?”

6. ✤ We backport fixes into stable branches from trunk
Ruby’s stable branch model
EoL
ruby_2_2
ruby_2_5
ruby_2_6
backport
trunk
bugfix

7. ✤ We backport fixes into stable branches from trunk
Ruby’s stable branch model
nurse
unak
Release
Manager
Stable
Branch
Maintainer
EoL
ruby_2_2
ruby_2_5
ruby_2_6
backport
trunk
bugfix
nagachika

8. ✤ Backport bug-fixes from trunk into stable branches
✤ Release stable packages.
✤ Handle security issues in concert with
stakeholders.
Stable Branch Maintainer

9. ✤ Backport bug-fixes from trunk into stable branches
✤ Release stable packages
✤ Handle security issues in concert with
stakeholders
Stable Branch Maintainer

10. ✤ Watch commits on trunk.
✤ Backport bug-fixes.
Stable Branch Maintainer’s daily work

11. ✤ Watch commits on trunk
→ Watch backport requests on Redmine.
✤ Backport bug-fixes.
Stable Branch Maintainer’s daily work

12. ✤ Redmine: bugs.ruby-lang.org
Ruby’s stable maintenance policy

13. ✤ File tickets with rubyʼs version information
Ruby’s stable maintenance policy

14. ✤ You can maintain only one stable branch at once.
Ruby’s stable branch model
nurse
nagachika
unak
Release
Manager
Stable
Branch
Maintainer
EoL
ruby_2_2
ruby_2_5
ruby_2_6
backport
trunk
bugfix

15. “How can I become a Ruby stable
maintainer?”

16. Requirements for Stable Branch Maintainers

17. ✤ Wide understandings for the Ruby implementation
✤ Sustainability to some extent
✤ Understanding maintenance policy
Requirements for Stable Branch Maintainers

18. ✤ Backport bug-fixes
✤ Donʼt backport new features/spec changes
Ruby’s maintenance policy
stable
trunk
bug-fix
new feature

19. IO.read could execute a command
IO.read(“|cmd…”) executes the command
(same as Kernel#open)

20. IO.read and File.read

21. IO.read and File.read

22. % ruby -ve 'puts File.read("|echo foo")'
ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-darwin15]
foo
% ruby -ve 'puts File.read("|echo foo")'
ruby 2.5.4p155 (2019-03-13 revision 67245) [x86_64-darwin15]
-e:1: warning: IO.read called on File to invoke external command
foo
% ruby -ve 'puts File.read("|echo foo")'
ruby 2.6.2p47 (2019-03-13 revision 67232) [x86_64-darwin15]
Traceback (most recent call last):
1: from -e:1:in `<main>'
-e:1:in `read': No such file or directory @ rb_sysopen - |echo foo (Errno::ENOENT)
IO.read and File.read

23. ✤ 2.0.0: 469
✤ 2.1: 250
✤ 2.2: 205
✤ 2.3: 217
✤ 2.4: 190
✤ 2.5: 101
Backport commits by nagachika

24. ✤ 2.0.0: 469
✤ 2.1: 250
✤ 2.2: 205
✤ 2.3: 217
✤ 2.4: 190
✤ 2.5: 101
Backport commits by nagachika
include
Documentation,
performance improvement,
memory usage improvement…

25. Lessons learned from
failures

26. Backport performance improvements

28. ✤ The change broke CI on mswin
Backport performance improvements

29. ✤ The lesson learned
✤ Donʼt backport performance improvements
Backport performance improvements

30. Backport introduced memory violation

31. Backport introduced memory violation

32. Backport introduced memory violation

33. ✤ The lesson learned
✤ Bug-fixes for Method/Constants search in edge
cases sometimes introduce another memory
violation.
✤ Fixing a minor bug can introduce severe bugs
Backport introduced memory violation

34. Refinements

35. Refinements

36. ✤ The lesson learned
✤ “Refinements” is not a matured feature and
continue expanding its scope of adaptation.
✤ Deal it carefully.
Refinements

37. Fixing SyntaxError caused another SyntaxError

38. Fixing SyntaxError caused another SyntaxError

39. Fixing SyntaxError caused another SyntaxError

40. cond ? expr1 :expr2
Fixing SyntaxError caused another SyntaxError
{ key:(expr rescue nil) }
{ key:<<EOF }
EOF

41. ✤ The lesson learned
✤ parse.y is “魔境” (mass of legendary complexity)
✤ SyntaxError is the one of the most severe issues
✤ Monkey patching cannot get rid of SyntaxError
Fixing SyntaxError caused another SyntaxError

42. Fixing SyntaxError caused another SyntaxError(2)

43. Fixing SyntaxError caused another SyntaxError(2)

44. Fixing SyntaxError caused another SyntaxError(2)

45. def foo key1:
…
end
Fixing SyntaxError caused another SyntaxError(2)
{ key:if foo then 1 else 0 }

46. ✤ The lesson learned(?)
✤ Fixing the SyntaxError introduced another
SyntaxError in the more rare case
✤ But the prior SyntaxError was in the new syntax
(Mandatory keyword arguments)
✤ There was maybe no real application affected
by the prior SyntaxError.
Fixing SyntaxError caused another SyntaxError(2)

47. Fixing SyntaxError caused another SyntaxError(3)

48. Fixing SyntaxError caused another SyntaxError(3)

49. Fixing SyntaxError caused another SyntaxError(3)

50. ✤ The lesson learned
✤ parse.y is “魔境”
✤ Long-standing bugs have less priority
→ “Long-standing” means thereʼs no real
application affected
✤ “Known bug” can be better than “Regression”
Fixing SyntaxError caused another SyntaxError(3)

51. Load FIFO

52. ✤ Release GVL during open fd for `load`
Load FIFO

53. ✤ Performance degradation of YAML.parse on
multi-threads environments
Load FIFO

54. ✤ The lesson learned
✤ Donʼt backport bug-fixes for imaginary use case.
No one wanted to load from FIFO!
Load FIFO

55. ✤ Donʼt backport performance improvements
✤ Donʼt backport fix for the long-standing bugs
✤ Donʼt jump at the fix in parse.y, constants/
methods search and refinements
✤ Donʼt backport fixes on one wanted to backport
The Lessons Learned from failures

56. ✤ Be-Practical!
The Lessons Learned from failures