as_stubbed_const causes Sorbet type error when stubbing .new with instance_double despite RSpec::Sorbet.allow_doubles!

[baka-san]

I'm running into a runtime TypeError from Sorbet when mocking a class constructor with as_stubbed_const, even though RSpec::Sorbet.allow_doubles! is enabled.

Problem

I'm testing a method that returns an instance of a class (Thing). In the spec, I:

• Stub Thing.new to return an thing_instance = instance_double(Thing)
• Use class_double(Thing, new: thing_instance).as_stubbed_const
• Enable RSpec::Sorbet.allow_doubles!

Despite that, Sorbet raises this error:

TypeError:
  Return value: Expected type Thing,
  got type RSpec::Mocks::InstanceVerifyingDouble with value #<InstanceDouble(Thing)>

However, if I remove class_double(Thing, new: thing_instance).as_stubbed_const and just do:

allow(Thing).to receive(:new).and_return(thing_instance)

…it works fine and Sorbet doesn’t complain.

Minimal Repro

# typed: true

class Thing
  extend T::Sig

  sig { params(name: String).void }
  def initialize(name:); end
end

class Widget
  extend T::Sig

  sig { params(name: String).returns(Thing) }
  def build(name)
    Thing.new(name: name)
  end
end

# spec/models/widget_spec.rb
require "rails_helper"
RSpec::Sorbet.allow_doubles!

RSpec.describe Widget do
  let(:thing_instance) { instance_double(Thing) }

  before do
    class_double(Thing, new: thing_instance).as_stubbed_const
  end

  it "returns a Thing" do
    result = Widget.new.build("hello")
    expect(result).to eq(thing_instance)
  end
end

Question

Is it expected that class_double(...).as_stubbed_const causes Sorbet to raise a type error when the class under test returns an instance_double of that class?

Calling allow(MyClass).to receive(:new).and_return(my_instance_double) works fine without as_stubbed_const, but adding as_stubbed_const leads to Sorbet rejecting the return value, even when RSpec::Sorbet.allow_doubles! is used.

Is this a known issue, or is there a recommended way to configure rspec-sorbet to allow this?

Thanks!