Type binding cannot be read from TASTY

[nicolasstucki]

When compiling from tasty (tests in tests/posFromTasty/)

trait Map2[K] {
  def get(k: K): K = k
  def foo: K = {
    this match {
      case that: Map2[b] => that.get(3.asInstanceOf[b])
      case that: Map2[b] => that.get(3.asInstanceOf[K])
      case _ => get(5.asInstanceOf[K])
    }
  }
}

When recompiling the code loaded from tasty, the references of b become redefinitions of b. There are also positions missing from.

[smarter]

This was previously discussed but not fully resolved in #2958

[nicolasstucki]

https://github.com/dotty-staging/dotty/tree/fix-bind-ambiguity has a first step that @DarkDimius implemented back then and some work I made on top to finish it. Unfortunately I currently a bit blocked on this one.

@DarkDimius do you still remember this issue and do you have some useful pointers?

[nicolasstucki]

After that file is compiled, we can reproduce the issue with dotc -from-tasty -classpath . Map2 -Ycheck:all or dotc -decompile -classpath . Map2