- TypeProf is a static type analyzer for Ruby that can infer types without annotations by analyzing code and tests. - A new TypeProf extension for VSCode provides modern IDE features like on-the-fly type checking, method signature hints, and error reporting without needing type annotations. - The extension demonstrates how TypeProf can enhance the development experience in Ruby by bringing features like autocompletion and error checking traditionally requiring type systems.

1. Enjoy Ruby Programming
in IDE and TypeProf
Yusuke Endoh (@mametter)
RubyConf 2021

2. Yusuke Endoh / @mametter
•A Ruby committer working at Cookpad w/ @ko1
•Main contribution so far:
• Designed and implemented keyword arguments
• Implemented test coverage feature
• Implementing TypeProf  Today's topic
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3. A recent contribution: error_highlight
3
json = { foo: { bar: { baz: 42 } } }
json[:foo][:barr][:baz]
# Ruby 3.0
$ ruby t.rb
t.rb:2:in `<main>': undefined method `[]' for nil:NilClass (NoMethodError)
# Ruby 3.1
$ ruby t.rb
t.rb:2:in `<main>': undefined method `[]' for nil:NilClass (NoMethodError)
json[:foo][:barr][:baz]
^^^^^^
Credit: The original author of its prototype is @yui-knk
https://github.com/ruby/ruby/pull/4470

4. Index
•What is TypeProf?
•TypeProf for IDE
•How to use TypeProf for IDE
•Conclusion
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5. TypeProf: A static analyzer for Ruby 3
•TypeProf analyzes non-annotated Ruby code
• guess types of method arguments and a return value
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class User
def initialize(name)
@name = name
end
end
User.new("John")
Ruby code
class User
def initialize:(String name)->void
end
RBS
TypeProf

6. TypeProf? RBS? Steep? Sorbet?
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Name What
RBS
TypeProf
Steep
Sorbet
The Ruby official type definition language
A static type analyzer for Ruby
A static type analyzer for Ruby
A static type analyzer for Ruby

7. Comparison between static analyzers
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TypeProf Steep Sorbet
Type inference Strong Weak Weak
Accuracy Weak Strong Strong
Analysis speed Slow Fast Very fast
RBS support Yes Yes Not yet
IDE support No → Yes Yes Yes

8. RBS: An official language for Ruby types
• Common complaint: "Header files suck"
• TypeProf for IDE may solve this issue
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class User
def initialize(name)
@name = name
end
end
User.new("John")
user.rb
class User
def initialize:
(String name) -> void
end
user.rbs

9. Index
•What is TypeProf?
•TypeProf for IDE
•How to use TypeProf for IDE
•Conclusion
9

10. Today's topic: TypeProf for IDE
10
VSCode TypeProf
code changed
error found
complete "5.ti"
maybe "5.times"
5.ti|
Do you mean:
5.times
1 + "str"
1 + "str"
Is this a bug?
• A VSCode extension for Ruby powered by TypeProf

11. Demo: TypeProf for IDE
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12. The modern development experience
with TypeProf for IDE
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On-the-fly method signature

13. The modern development experience
with TypeProf for IDE
13
On-the-fly error reporting

14. The modern development experience
with TypeProf for IDE
14

15. The modern development experience
with TypeProf for IDE
15
On-the-fly type inference
Completion

16. The modern development experience
with TypeProf for IDE
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Hint for arguments

17. Demo: Summary
•Modern development experience comes to Ruby
without type annotations
•RBS are interspersed to Ruby files
• One possible answer to "Header files suck"
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18. Index
•What is TypeProf?
•TypeProf for IDE
•How to use TypeProf for IDE
•Conclusion
18

19. How to configure TypeProf for IDE
• Use ruby 3.1.0-dev (development version☺)
• Add for your Gemfile
• Configure RBS collection
• if you use gems
• Install VSCode extension→
• search "typeprof"
• Open your folder with VSCode and pray
• More detail: https://github.com/ruby/typeprof/blob/master/doc/ide.md
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gem "typeprof"

20. Protips™
•Write a simple test in a file
•Write RBS 😞
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21. Demo: Tests instead of type annotations
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untyped
String

22. Demo: Passing an unknown type
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The method signature is changed
to accept a new type
Error in the callee side

23. Demo: Manual RBS specification
23
Click here
A prototype RBS is
created

24. Demo: Manual RBS specification (cont'd)
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Error in the caller side
# means RBS-defined

25. Protips™
•Write a simple test in a file
• TypeProf requires a test to guess method signatures
•Write RBS to fix method signatures (if needed)
• This makes TypeProf analysis faster
• This is also useful to make TypeProf faster
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26. Index
•What is TypeProf?
•TypeProf for IDE
•How to use TypeProf for IDE
•Conclusion
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27. Release plan
•TypeProf for IDE will be released in Ruby 3.1
• Happy if you could play with it and give us feedback
•Ready for production?
• Experimental, but hopefully works for small programs
• For large code base, please write RBS for gems first!
• https://github.com/ruby/gem_rbs_collection
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28. Special thanks
•Hideki Miura
•Ruby committers: matz, akr, ko1, soutaro
•Katsuhiro Ueno & Eijiro Sumii
•Stripe team & Shopify team & Jeff Foster
•Yuta Saito (@kateinoigakukun)
• Many improvements of TypeProf for IDE
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29. Conclusion
•The modern development experience is possible
without full type annotations by TypeProf for IDE
•Ruby 3.1 will bundle TypeProf for IDE
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