T.cast is not "useless" when used to narrow an untyped type

[jez]

Input

→ View on sorbet.run

# typed: strict
extend T::Sig


class A; end
class B < A; end

my_b = T.let(B.new, B)
original = T.let({}, T::Hash[Symbol, String])
a = T.cast(original, T::Hash[Symbol, T.untyped])
a = T.let(original, T::Hash[Symbol, T.untyped])
a = T.cast('string', T.untyped)
a = T.let('string', T.untyped)

Observed output

editor.rb:10: T.cast is useless because T::Hash[Symbol, String] is already a subtype of T::Hash[Symbol, T.untyped] https://srb.help/7015
    10 |a = T.cast(original, T::Hash[Symbol, T.untyped])
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  Got T::Hash[Symbol, String] originating from:
    editor.rb:9:
     9 |original = T.let({}, T::Hash[Symbol, String])
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  Autocorrect: Use -a to autocorrect
    editor.rb:10: Replace with original
    10 |a = T.cast(original, T::Hash[Symbol, T.untyped])
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

editor.rb:12: Please use T.unsafe to cast to T.untyped https://srb.help/7015
    12 |a = T.cast('string', T.untyped)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  Autocorrect: Use -a to autocorrect
    editor.rb:12: Replace with T.unsafe('string')
    12 |a = T.cast('string', T.untyped)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
Errors: 2

Expected behavior

In this case, the type specified in the T.cast is better than the untyped Hash.

Sorbet should suggest changing the T.cast to T.let instead of removing the T.cast entirely.

---

[jez]

Another example

Input

→ View on sorbet.run

# typed: true
class Foo
  extend T::Sig

  sig {
    params(
      proc: T.nilable(T.proc.params(foo: String, bar: String).void)
    ).void
  }
  def initialize(proc: nil)
    if proc.nil?
      proc = T.let(->(foo,bar) {}, T.proc.params(foo: String, bar: String).void)
    end
    @proc = proc
  end
end

Observed output

No errors! Great job.