rewriter::Flatten pulls sig call out of method body even if it's not actually a method signature

[jez]

Input

→ View on sorbet.run

# typed: true

class A
  extend T::Sig

  def foo(x)
    x.sig { void }
  end
end

Observed output

class <emptyTree><<C <root>>> < (::<todo sym>)
  class <emptyTree>::<C A><<C <todo sym>>> < (::<todo sym>)
    def foo<<todo method>>(x, &<blk>)
      nil
    end

    x.sig() do ||
      <self>.void()
    end

    <self>.extend(<emptyTree>::<C T>::<C Sig>)

    <runtime method definition of foo>
  end
end
editor.rb:7: Method sig does not exist on NilClass https://srb.help/7003
     7 |    x.sig { void }
              ^^^
  Got NilClass originating from:
    editor.rb:3: Possibly uninitialized (NilClass) in:
     3 |class A
     4 |  extend T::Sig
     5 |
     6 |  def foo(x)
     7 |    x.sig { void }
     8 |  end
     9 |end

editor.rb:7: Method void does not exist on T.class_of(A) https://srb.help/7003
     7 |    x.sig { void }
                    ^^^^
  Did you mean load? Use -a to autocorrect
    editor.rb:7: Replace with load
     7 |    x.sig { void }
                    ^^^^
    https://github.com/sorbet/sorbet/tree/master/rbi/core/kernel.rbi#L1664: Defined here
    1664 |  def load(filename, arg0=T.unsafe(nil)); end
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Errors: 2

Expected behavior

Sorbet pulls the x.sig { void } call out to the top level of the class definition in an attempt to flatten all nested method definitions. That's not what should have happened—this method call doesn't actually match what a sig would look like, nor is there a call to a method immediately after this sig call.

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