The State of Ruby Static Typing at Shopify

The State of Ruby Static Typing at Shopify

Shopify changes a lot. We merge around 400 commits to the main branch daily and deploy a new version of our core monolith 40 times a day. The Monolith is also big: 37,000 Ruby files, 622,000 methods, more than 2,000,000 calls. At this scale with a dynamic language, even with the most rigorous review process and over 150,000 automated tests, it’s a challenge to ensure everything works properly. Developers benefit from a short feedback loop to ensure the stability of our monolith for our merchants.

Since 2018, our Ruby Infrastructure team has looked at ways to make the development process safer, faster, and more enjoyable for Ruby developers. While Ruby is different from other languages and brings amazing features allowing Shopify to be what it is today, we felt there was a feature from other languages missing: static typing.

Shipit! Presents: The State of Ruby Static Typing at Shopify

On November 25, 2020, Shipit!, our monthly event series, presented The State of Ruby Static Typing at Shopify. Alexandre Terrasa and I talked about the history of static typing at Shopify and our adoption of Sorbet.

We weren't able to answer all the questions during the event, so we've included answers to them below.

What are some challenges with adopting Sorbet? What was some code you could not type?

So far most of our problems are in modules that use ActiveSupport::Concern (many layers deep, even) and modules that assume they will be included in a certain kind of class, but have no way of making that explicit. For example, a module that assumes it will be included in an ActiveRecord model could be calling before_save to add a hook, but Sorbet would have no idea where before_save is defined. We are also looking to make those kinds of dependencies between modules and include sites explicit in Sorbet.

Inclusion requirements is also something we’re trying to fix right now, mostly for our helpers. The problem is explained in the description of this pull-request: https://github.com/sorbet/sorbet/pull/3409.

If a method has an array in argument, do you have to specify it is an array of what type? And if not, how do Sorbet makes the method you call on the array's element exists?

It depends on the type of elements inside the array. For simple types like Integer or Foo, you can easily type it as T::Array[Integer] and Sorbet will be able to type check method calls. For more complex types like arrays containing hashes it depends, you may use T::Array[T.untyped] in which case Sorbet won’t be able to check the calls. Using T.untyped you can go as deep and precise you want it to be: T::Array[T::Hash[String, T.untyped]], T::Array[T::Hash[String, T::Array[T.untyped]]], T::Array[T::Hash[String, T::Array[Integer]]] and Sorbet will check the calls on what it knows about. Note that as your type becomes more and more complex, maybe you should start thinking about making a class about it so you can just use T::Array[MyNewClass].

How would you compare the benefits of Sorbet to Ruby relative to the benefits of Typescript to Javascript?

There are similar benefits, but Ruby is a much more dynamic language than JavaScript and Sorbet is a much younger project than TypeScript. So the coverage of Ruby features and expressiveness of the type system of Sorbet lags behind the same benefits that TypeScript brings to JavaScript.On the other hand, Sorbet annotations are pure Ruby. That means you don’t have to learn a new language and you can keep using your existing editors and tooling to work with it. There is also no compilation of Ruby code with types to plain Ruby, like how you need to compile TypeScript to JavaScript. Finally, Sorbet also has a runtime type-checker and it can verify your types and alert you if they don’t check when your application is running, which is a great additional safety that TypeScript does not have.

Could you quickly relate Sorbet with RBS and what is the future of sorbet after Ruby 3.0?

Stripe gave an interesting answer to this question: https://sorbet.org/blog/2020/07/30/ruby-3-rbs-sorbet. RBS is about the language to write the signatures, you still need a type checker to check those signatures against your code. We see Sorbet as one of the solution that can use those types, and currently it’s the fastest solution. One limitation of RBS is the lack of inline type annotations, for example there is no syntax to cast a variable to another type. So type checkers have to use additional syntax to make this possible. Even if Sorbet doesn’t support RBS at the moment, it might in the future. And in the case it never happens, remember that it’s easier to go from one type specification to another rather than an untyped codebase to a typed one. So all the efforts are not lost.

Does Tapioca support Enums etc?

Tapioca is able to generate RBI files for T::Enum definitions coming from gems. It can also generate method definitions for the ActiveRecord enums as DSL generators.

In which scenarios would you NOT use Sorbet?

I guess the one scenario where using Sorbet would be counterproductive is if there is no team buy-in for adopting Sorbet. If I were on such a team and I couldn’t convince the rest of the team of the utility of it, I would not push to use Sorbet.Other than that, I can only think of a code base that has a LOT of metaprogramming idioms to be a bad target for using Sorbet. You would still get some benefits from even running Sorbet at typed: false but it might not be worth the effort.

What editors do you personally use? Any standardization across the organization?

We have not standardized on a single editor across the company and we probably will not do so, since we believe in developers’ freedom to use the tools that make them the most productive. However, we also cannot build tooling for all editors, either. So, most of our developer acceleration team builds tooling primarily for VSCode, today. Ufuk personally uses VSCode and Alex uses VIM.

Is there a roadmap for RBI -> RBS conversion for when Ruby 3.0 comes out?

No official roadmap yet, we’re still experimenting with this on the side of our main project: 100% typed: true files in our monolith. We can already say that some features from RBS will not directly translate to RBI and vice versa. You can see a comparison of both specifications here: https://github.com/Shopify/rbs_parser#whats-supported (might not be completely up-to-date with the latest version of RBS).

What are the major challenges you had or are having with Ruby GraphQL libraries?

Our team tried to marry the GraphQL typing system and the Sorbet types using RBI generation but we got stuck in some very dynamic usages of GraphQL resolvers, so we paused that work for now. On the other hand, there are teams within Shopify who have been using Sorbet and GraphQL together by changing the way they write GraphQL endpoints. You can read more about the technical details of that from the blog post of one of the Shopify engineers that has worked on that: https://gmalette.dev/posts/graphql-and-sorbet-and-unit-tests/.

What would be the first step in getting started with typing in a Rails project? What are kind of files that should be checked in to a repo?

The fastest way to start is to use the steps listed on the Sorbet site to start running with Sorbet. After doing that, you can take a look at using sorbet-rails to generate Rails RBI files for you, or you can look at tapioca to generate gem RBIs. Since you can go gradual it’s totally up to you.

Our advice would be to first target all files at typed: false. If you use tapioca, the price is really low and already brings a lot of benefit. Then try to move the files to type: true where it does not create new type errors (you can use spoom for that: https://github.com/Shopify/spoom#change-the-sigil-used-in-files).

When it comes to adding signatures, prefer the files that are the most reused or, if you track the errors from production, going first with the files that create the most errors might be a good choice. Files touched by many teams are also an interesting target as signatures make collaboration easier. Files with a lot of churn. Or files defining methods reused a lot across your codebase.

As for the files that you need to check-in to a repository, the best practice is to check-in all the files (mostly RBI files) generated by Sorbet and/or tapioca/sorbet-typed. Those files enable the code to be type checked, so should be available to all the developers that work on the code base.

Additional Information

Open Source


We're planning to DOUBLE our engineering team in 2021 by hiring 2,021 new technical roles (see what we did there?). Our platform handled record-breaking sales over BFCM and commerce isn't slowing down. Help us scale & make commerce better for everyone.