TypeProf for IDE: Enrich Development Experience without Annotations

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TypeProf for IDE: Enrich Development Experience without Annotations Yusuke Endoh (@mametter) RubyKaigi Takeout 2021

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Yusuke Endoh / @mametter •A Ruby committer working at Cookpad w/ @ko1 • TypeProf: A static type analyzer for Ruby 3 •An esoteric Ruby programmer • See my RubyKaigi bio 2

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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 `': undefined method `[]' for nil:NilClass (NoMethodError) # Ruby 3.1 $ ruby t.rb t.rb:2:in `': 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

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"I love static typing" … or do you? •Static typing is a means, not an end •The end is the modern development experience • Demo: TypeScript 4

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The modern development experience with TypeScript 5 On-the-fly error reporting

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The modern development experience with TypeScript 6 On-the-fly type inference

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The modern development experience with TypeScript 7 Go to definition

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The modern development experience with TypeScript 8 •Completion Completion

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The modern development experience with TypeScript 9 Hint for arguments

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"I love static typing" … or do you? •Static typing is a means, not an end • The end is the modern development experience • On-the-fly error reporting, go-to-definition, completion, argument hint, etc. •Q: Isn't it possible to achieve the experience without changing the Ruby language? • My answer is "Possible!" 10 (under some conditions)

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Today's topic: TypeProf for IDE •A VSCode extension for Ruby • Powered by TypeProf (a static type analyzer for Ruby) •Demo 11

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The modern development experience with TypeProf for IDE 12 On-the-fly method signature

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

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The modern development experience with TypeProf for IDE 14

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

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

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Demo: Summary •The modern development experience is possible without full type annotations by TypeProf for IDE 17

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Agenda ➔ Recap: Types for Ruby 3  •TypeProf • TypeProf for IDE • Conclusion 18

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Recap: Types for Ruby 3 19 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

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RBS: Ruby official type definition language 20 class User def initialize: (String) -> void def name: () -> String end

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What a static type analyzer does •Infers the types of a given program • Reports a potential runtime type error • Supports IDE 21 msg = "Hello, " + user.name msg: String msg = "Hello, " + user.naame Error!

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Differences of each static analyzer 22 Type inference Error reporting IDE support Analysis speed TypeProf 🙂Strong ☹️Weak No → Yes ☹️Slow Steep ☹️Weak 🙂Strong Yes 🙂Fast

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Agenda •Recap: Types for Ruby 3 ➔ TypeProf  • TypeProf for IDE • Conclusion 23

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The key idea of TypeProf Runs a Ruby code in "type-level" Traditional interpreter def foo(n) n.to_s end foo(42) Calls w/ 42 Returns "42" TypeProf def foo(n) n.to_s end foo(42) Calls w/ Integer Returns String Object#foo :: (Integer) -> String 24

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The user-facing feature of TypeProf •Ruby 3.0 • A type inference tool to create a prototype of RBS • No IDE support • Ruby 3.1~ • + IDE support! 25

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Demo (memo) •Test instead of type annotations •Passing an unknown type • Manual RBS specification • Flow-sensitive analysis • Manual overloading •Block, RBSWiki example 26

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Demo: Tests instead of type annotations 27 untyped String

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Demo: Passing an unknown type 28 The method signature is changed to accept a new type Error in the callee side

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Demo: Manual RBS specification 29 Click here A prototype RBS is created

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Demo: Manual RBS specification (cont'd) 30 Error in the caller side # means RBS-defined

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Demo: Flow-sensitive analysis 31 No error type case

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Demo: Manual overloading 32 No error Write RBS for overloading Argument hint is selectable

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Demo: Block 33

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Demo: Works with a simple Rack app 34

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Agenda •Recap: Types for Ruby 3 •TypeProf ➔TypeProf for IDE • Conclusion 35

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Language Server Protocol (LSP) 36 LSP client (vscode) LSP server (TypeProf for IDE) 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?

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Currently supported LSP features •Show method signatures •Show potential errors • Go to definition of methods/variables • Find references of methods/variables • Completion •Show hint about method arguments 37

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Not-implemented-yet LSP Features 38 Type hover Documentation • More challenging features • Auto refactoring (renaming), quick fix suggestion, etc. • Contribution is welcome!!!

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Future work: the parser needs more ♥ •An AST node knows only the beginning and end of the source code • The parser returns nothing when syntax is broken • Cannot complete an incomplete call 39 current implementation desired behavior foo(k:)

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About analysis performance •TypeProf is very slow • It traces "require 'foo'" (even if it is a gem) •TypeProf for IDE stops the analysis in one second • Nothing will be reported where it couldn't analyze within the time limit 40

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How to make TypeProf fast •Write RBS for gems • so that TypeProf don't have to analyze gem sources • Watch pocke's talk (Day 2) • Divide your application to components • and write RBS against their interfaces • We need experiment with a practical use case 41

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Agenda •Recap: Types for Ruby 3 •TypeProf • TypeProf for IDE • Implementation ➔Conclusion 42

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Release plan •TypeProf for IDE will be released in Ruby 3.1 • Happy if you could play with it and give us feedback • How to run the development version https://gist.github.com/mame/86234de6a58352b9f994e0f8a6d6fbc2 (in Japanese) •Ready for production? • Experimental, but hopefully works for small programs • For large code base, please write RBS for gems first! 43

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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 44

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Conclusion •The modern development experience is possible without full type annotations by TypeProf for IDE •Ruby 3.1 will bundle TypeProf for IDE 45