Let's write RBS! RubyKaigi 2023
 13th May


● Work for Money Forward, Inc. ○ a Rails app engineer ○ an RBS maintainer ● Live in Okayama ● NOT flat earth believer Masataka Pocke Kuwabara GitHub: @pocke Twitter: @p_ck_ @[email protected]

Before this talk, thanks for all RBS contributors!👏👏 4geru, AaronLasseigne, DmitryPogrebnoy, HoneyryderChuck, M-Yamashita01, MITSUBOSHI, MSP-Greg, POPPIN-FUMI, ParadoxV5, TsubasaKawajiri, VTRyo, akito-fujisaki, autopp, buzztaiki, castwide, cky, coorasse, craftscat, dleavitt, fabon-f, fugakkbn, hana-da, hanazuki, hjwylde, hsbt, ioquatix, joker1007, kachick, kaiquekandykoga, kenchan, koic, kotaokubo, koukikitamura, ksss, kymmt90, lauratpa, m11o, mame, meqif, myronmarston, nipe0324, nobu, nogtk, nurse, nvh0412, osatoh, osyo-manga, palkan, paracycle, piotaixr, pocke, raosush, rmitchell-sq, sadgb, sanfrecce-osaka, sevenc-nanashi, shugo, snaka, soutaro, sue445, takahashim, tatematsu-k, thinca, tisonkun, tlvu2697, ujihisa, unasuke, ursm, yassenb, ybiquitous, ydah, yyamanoi1222, yykamei, znz All contributors to ruby/rbs and ruby/gem_rbs_collection from the previous list in the past Kaigi to RBS 3.1 except dependabot.
 This is generated with the following script: https://gist.github.com/pocke/ef809d411bd7f26f02e5850d44db82f2


Agenda

Agenda This talks has two parts.
 ● Part 1: Introduce RBS features
 ○ Introduce new features of RBS 3.1
 ○ Introduce rbs tools to write signatures (I don't have enough time!)
 ● Part 2: Demonstrate writing RBS
 ○ in an application
 ○ in ruby/rbs repository (I don't have enough time!)


● RBS basics
 ○ syntax, usage, etc
 ○ rbs collection
 ● RBS related tools
 ○ Steep, RBS Rails, etc
 I wrote an article to learn them (Japanese). https://pocke.hatenablog.com/entry/2023/ 05/08/184814
 What I will NOT talk about in this presentation

The new features of RBS 3.1

rbs subtract

What is rbs subtract rbs subtract removes duplicate RBS definitions.
 Usage:
 # Display the result of (a.rbs - b.rbs) $ rbs subtract a.rbs b.rbs # Overwrite a.rbs with the result directly $ rbs subtract --write a.rbs b.rbs This feature was developed by Saito-san (@tadd), and I took over it.

rbs subtract behavior $ rbs subtract a.rbs b.rbs # output (a.rbs - b.rbs) class C def bar: () -> untyped end # a.rbs class C def foo: () -> untyped def bar: () -> untyped end # b.rbs class C def foo: () -> Integer end You can find more examples from https://github.com/ruby/rbs/blob/master/test/rbs/subtractor_test.rb


Why rbs subtract is necessary It is necessary to modify auto-generated RBS files in a maintainable way.


● You are developing a large Ruby app, and you want to introduce RBS to the app.
 ● You run an RBS generator.
 ○ It generate RBS files from your codebase.
 ○ Generator is necessary because it's hard to write RBS files for entire application.
 Why necessary: example situation

Generated code is not perfect.
 $ cat test.rb class C def foo(int) = int.to_s end $ rbs prototype rb test.rb class C def foo: (untyped int) -> untyped end Why necessary: generated RBS

If you write a method definition to a separate file, you will get a duplication error.
 Why necessary: problem # auto-generated.rbs class C def foo: (untyped int) -> untyped end # hand-written.rbs class C def foo: (Integer int) -> String end # ::C#foo has duplicated definitions in hand-written.rbs

rbs subtract solves this problem.
 It removes well-described method definitions from auto-generated RBS files.
 
 Why necessary: solution # auto-generated.rbs class C def foo: (untyped int) -> untyped end # hand-written.rbs class C def foo: (Integer int) -> String end # subtracted.rbs class C # No `foo` definition end

# Generate RBSs for all Ruby code under sig/prototype directory $ rbs prototype rb --out-dir=sig/prototype --base-dir=. app lib # Write type definitions by hand $ $EDITOR sig/hand-written/foo.rbs # Remove hand-written methods from generated RBSs $ rbs subtract --write sig/prototype sig/rbs_rails sig/hand-written # Type-check with the RBS files $ steep check A simple example workflow

This feature is implemented in ruby/rbs#1287.
 The design is described in a HackMD document. https://hackmd.io/seoMijXwRdG2uFITm2lLq w
 For more information

rbs parse

What is rbs parse ● rbs parse parses a .rbs file and report syntax errors.
 $ rbs parse valid.rbs # Print nothing $ rbs parse invalid.rbs test.rbs:4:0...4:3: Syntax error: cannot start a declaration, token=`end` (kEND) This feature is available since the first release (ruby/rbs#207).


What's New Two kinds of options has been available since RBS v3.1 (ruby/rbs#1252).
 ● -e CODE ○ Same as Ruby.
 ○ We can use this command without saving RBS code to a file.
 ● --type, --method-type ○ It specifies parsing context.


Unfortunately I do not have enough time. Skip the next slides…

Example: -e Previously we need to save RBS code to a file to run rbs parse
 $ $EDITOR test.rbs && rbs parse test.rbs Since RBS 3.1, you do not need to save a file.
 $ rbs parse -e "class C end"

Example: --type and --method-type These option is useful with -e.
 # Check whole RBS code $ rbs parse -e "class C def f: (Integer) -> { code: Integer } end" # Check only method type $ rbs parse --method-type -e "(Integer) -> { code: Integer }" # Check only type $ rbs parse --type -e "{ code: Integer }"

Other tools (skip)

rbs collection ● It manages dependent libraries' RBSs.
 ● In short, Bundler for RBS.
 See my slides at RubyKaigi Takeout 2021 for more details https://rubykaigi.org/2021-tak eout/presentations/p_ck_.html


rbs prototype rbs prototype generates RBS from Ruby code.
 I use rbs prototype rb in the demo.


Other tools I also uses the following tools in the demonstration.
 ● Steep
 ○ Steep is a type checker working on RBS.
 ○ https://github.com/soutaro/steep
 ● RBS Rails
 ○ RBS Rails is an RBS generator for Rails applications.
 ○ https://github.com/pocke/rbs_rails


Editor integrations

Editor Integrations Today I use VS Code and the following two extensions for the demonstration.
 ● RBS Syntax
 ● Steep
 But you can also uses other editors that support LSP.
 https://github.com/ruby/rbs/blob/master/d ocs/tools.md
 


Demonstrations

Demonstrations There are two one demos.
 ● Introduce RBS to an existing app
 ○ On ruby/rubyci
 ● Show development experience using RBS
 ○ On ruby/rbs


https://github.com/ruby/rubyci
 1. Introduce rbs collection
 2. Introduce Steep
 3. Introduce rbs subtract
 4. Write .rbs files with subtract
 Introduce RBS to an existing app

After Events

【Money Forward x Shippio】 BaySide Tech Nite ● Shippio and Money Forward host this event.
 ● Talk about RubyKaigi and Ruby in English
 ● 2023-05-19 Tokyo
 https://moneyforward.connpass.co m/event/281065/
 Unfortunately I cannot attend this event😢


● I, mame-san, and sinsoku-san will talk about OSS contribution in this event.
 ● 2023-05-25 Tokyo and Online
 ● Talk in Japanese
 https://timeedev.connpass.com/event/ 279568/
 
 
 OSSへのコントリビュート - Techmee vol.7 (Contribute to OSS)

Conclusion

● I shared new features of RBS 3.1 ○ rbs subtract is a useful tool when you introduce RBS to a large app.
 ○ rbs prase evolved with new options.
 ● I shared demonstrations of introducing RBS.
 
 Thanks for listening to my talk!
 Conclusion \ WE ARE HIRING / Scan to apply now!