`T.self_type` does not work for union types (e.g. `T::Boolean#tap` returns `TrueClass`)

[ipvalverde]

Input

→ View on sorbet.run

# typed: true
extend T::Sig

my_boolean = rand(10).even?

boolean_tap_result = my_boolean.tap { puts "Do nothing" }
T.reveal_type(boolean_tap_result) # <== TrueClass!?


MyUnionType = T.type_alias { T.any(String, Integer) }

union_type_instance =
  if rand(10).even?
    "Hey there!"
  else
    1
  end

union_type_tap_result = union_type_instance.tap { puts "Do nothing" }
T.reveal_type(union_type_tap_result) # <== Integer!?

Observed output

editor.rb:7: Revealed type: TrueClass https://srb.help/7014
     7 |T.reveal_type(boolean_tap_result) # <== TrueClass!?
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  Got TrueClass originating from:
    editor.rb:6:
     6 |boolean_tap_result = my_boolean.tap { puts "Do nothing" }
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

editor.rb:20: Revealed type: Integer https://srb.help/7014
    20 |T.reveal_type(union_type_tap_result) # <== Integer!?
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  Got Integer originating from:
    editor.rb:19:
    19 |union_type_tap_result = union_type_instance.tap { puts "Do nothing" }
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Errors: 2

Expected behavior

The T.self_type should respect the union type. So instead of just retuning a (random?!) type from the union, it should return the whole union type definition.

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