Add a json_api_client DSL compiler

[lavoiesl]

Motivation

Fixes #1554

This could perhaps be implemented in https://github.com/JsonApiClient/json_api_client as a tapioca extension, but it's worth noting that the gem is used in several places at Shopify and is the spec used by the Vault API, namely used in iHub.

Implementation

The implementation was largely cargo-culted from the smart-properties compiler.

I paired with @Morriar

See comments for some of the design decisions.

[lavoiesl]

Disabled rubocop rule because it was a false positive

[lavoiesl]

There is a test for this

[lavoiesl]

Unfortunately, all of those things can be nullable when an object is created without being loaded via the API

[lavoiesl]

Properties with default values are always initialized with their default value, even when creating a bare object.

We made the decision to make those properties non-nilable to make the usage cleaner.

That being said, it is possible today to have a nil:

class User < JsonApiClient::Resource
  property :name, type: :string, default: "foo"
end

> u = User.new
=> #<User:@attributes={"type"=>"users", "name"=>"foo"}>

> u.name
=> "foo"

> u.name = 123
=> 123

> u.name # Casts to string
=> "123"

> u.name = nil

> u.name # Actually nil
=> nil

[KaanOzkan]

Don't have context on json_api_client but the compiler mostly LGTM.

I'm not sure if it should be a default compiler inside tapioca though 😕 I'll discuss with the team.

[KaanOzkan]

Should we rescue and rethrow a better error telling the user that the association is broken?

[lavoiesl]

That's what I wanted to do at first, but @Morriar 's argument was that this would show a stack within the gem, with a full stack trace, instead of us catching it. It's a problem of the user misusing the gem, not misusing tapioca/sorbet.

Another point is that this is forward compatible. If the gem changes its implementation, we don't have to change anything.

I'm okay either way, just highlighting the discussion.

[paracycle]

We have a way for compilers to signal errors that we use in AR associations compiler, for example:

tapioca/lib/tapioca/dsl/compilers/active_record_associations.rb

Lines 168 to 176 in bc6805e

	rescue SourceReflectionError
	add_error(<<~MSG.strip)
	Cannot generate association `#{reflection.name}` on `#{constant}` since the source of the through association is missing.
	MSG
	rescue MissingConstantError => error
	add_error(<<~MSG.strip)
	Cannot generate association `#{declaration(reflection)}` on `#{constant}` since the constant `#{error.class_name}` does not exist.
	MSG
	end

[paracycle]

The problem with raising an exception in a compiler is that the end-user has very little control over the cause of the exception (especially if the code is not under their control, like when the constant is coming from a gem) but their whole DSL generation process is now interrupted, so they can't finish generating all their DSL RBI files.