Stack overflow on `member` of some refined types.

[nicolasstucki]

The following type will generate a stack overflow when we call member on it.

   val badType =
      RefinedType(
        ctx.requiredClassRef("scala.collection.AbstractIterator"),
        "GroupedIterator".toTypeName,
        TypeRef(ctx.requiredClassRef("scala.collection.AbstractIterator"), "GroupedIterator".toTypeName))

    badType.member("GroupedIterator".toTypeName)

This a blocker for #1840 and only started happening after rebasing on the new bootstrap.

I have set up a simple test in this branch to reproduce the bug with sbt "testOnly dotc.tests".

Looking at the stack it is possible to see that it loops over glb making the types larger each time.

[nicolasstucki]

@odersky, could you have a look at this one, it is a minimized version of the blocker for the call graph that we talked about last week.

[nicolasstucki]

I also noticed that this only happens on inner classes that have a type parameter.

[odersky]

@nicolasstucki Can you provide more context? I tried to reconstruct your description in this test case:

import dotty.tools.dotc._
import core._
import Types._
import Contexts._
import Symbols._
import Decorators._

object Test {
  def f(implicit ctx: Context) = {
    val badType =
      RefinedType(
        ctx.requiredClassRef("scala.collection.AbstractIterator"),
        "GroupedIterator".toTypeName,
        TypeRef(ctx.requiredClassRef("scala.collection.AbstractIterator"), "GroupedIterator".toTypeName))
    badType.member("bar".toTermName)
  }
  def main(args: Array[String]): Unit = {
    implicit val ctx = (new ContextBase).initialCtx
    ctx.base.initialize()
    f
  }
}

But that one runs OK, no StackOverflow. It would be good to have a self-contained test case that exhibits the problem.

[nicolasstucki]

Try to run the tests in the branch that is in the link above.

[odersky]

No, I need more control over the compiler. So it would be great to have a self-contained test.

[nicolasstucki]

I will try to make it self contained.

[odersky]

I found it. You get the stackoverflow if you do a member with the type name "GroupedIterator" instead of the term name "bar".

[odersky]

... and I think I also found the cause: It's a type name refinement with a value type as the refined info. This should never happen. You need to insert a TypeAlias like this:

      RefinedType(
        ctx.requiredClassRef("scala.collection.AbstractIterator"),
        "GroupedIterator".toTypeName,
        TypeAlias(TypeRef(ctx.requiredClassRef("scala.collection.AbstractIterator"), "GroupedIterator".toTypeName)))

It would be good to put an assertion in the constructor of RefinedType that verifies that
term refinements come with term types and type refinements come with type types. Let me try to add that.

[DarkDimius]

AFAIK this is resolved. Please re-open if it isn't.