Unable to import and use a namespaced effect because of escaping its lexical scope

[Jiří Beneš]

This bug was originally discovered when attempting to use the network library from #432, but the bug is independent of that PR.

The issue requires two files to reproduce:

module mystate

namespace internal {
  interface State {
    def get(): Int
    def set(a: Int): Unit
  }

  def withState[R](a: Int) { prog: => R / State }: R = {
    var ref = a
    try { prog() }
    with State {
      def get() = resume(ref)
      def set(a: Int) = {
        ref = a
        resume(())
      }
    }
  }
}

module other

import mystate

def foo(): Unit / internal::State = {
  val n = do internal::get()
  do internal::set(n + 42)
}

The compiler is very dissatisfied with this function and reports the following error:

Effect State leaves its defining lexical scope as part of the inferred type

However, if you inline the mystate directly, no error is reported and everything works!