Autocorrect: when T::Boolean to when true, false

[jez]

Input

→ View on sorbet.run

# typed: true
extend T::Sig

sig {params(x: T.any(T::Boolean, String)).void}
def example(x)
  case x
  when T::Boolean
    T.reveal_type(x)
  end

  case x
  when true, false
    T.reveal_type(x)
  end
end

Observed output

editor.rb:7: Call to method === on T::Boolean mistakes a type for a value https://srb.help/7030
     7 |  when T::Boolean
               ^^^^^^^^^^

editor.rb:8: Revealed type: T.any(TrueClass, FalseClass, String) https://srb.help/7014
     8 |    T.reveal_type(x)
            ^^^^^^^^^^^^^^^^
  Got T.any(TrueClass, FalseClass, String) originating from:
    editor.rb:5:
     5 |def example(x)
                    ^

editor.rb:13: Revealed type: T::Boolean https://srb.help/7014
    13 |    T.reveal_type(x)
            ^^^^^^^^^^^^^^^^
  Got T::Boolean originating from:
    editor.rb:5:
     5 |def example(x)
                    ^
    editor.rb:12:
    12 |  when true, false
                     ^^^^^
Errors: 3

Expected behavior

It would be great if we could get an autocorrect to convert the when T::Boolean into when true, false, because this is a common error.

---

[amomchilov]

Would it be reasonable to implement === so this "just works"?

There's a real stigma against a bool type in Ruby, but if we're going to have a type system that has a bool type anyway, may as well use it, right?

[jez]

We have resisted implementing support for === on type objects, because there are type objects where it doesn't make sense, for example generic types, proc types, T.self_type, etc. which can't be checked at runtime (docs).