Infinity loop on compileIncremental stage after switching to 3.0.0-M1

[catap]

I'm switching one project to 3.0.0-M1 from 0.27.0-RC1.

The steps:

1. update sbt plugin from 0.4.2 to 0.4.6
2. update scala version from 0.27.0-RC1 to 3.0.0-M1

After the first step everything is fine, but when I switched to 3.0.0-M1 sbt is stuck on compileIncremental phase.

This project compiles for dozen of seconds, like 10-15, so I start panic after a few minutes of compileIncremental.

I've attached a few pictures from attached JProfile to show where it is looping.

[bishabosha]

Hello, please may you try and find the smallest set of code that triggers this issue and update this issue with the code

[odersky]

That stacktrace looks familiar... I think it is already fixed by #10271.

@catap Would it be possible to try this with the current nightly?

[catap]

@odersky yes and testing a night-build is much better idea than start to cutting a lot of code to discover that is broking the compiler.

[odersky]

Do you by any chance have union types with many alternatives? That's what borke in the other issue.

[catap]

@odersky this is code that is cross compiling to 2.11, 2.12, 2.13 and now 3.0.0/0.27, so, not any union types or new features from scala3.

And I'd like to confirm that 3.0.0-M2-bin-20201115-3c04f9b-NIGHTLY is fixing the issue.

[catap]

At my case it is triggered by creation a a field inside an object that is called BytesStream [here it is important because it has a lot of cross-references] that looks like:

val DESERIALIZERS: Map[BytesStream.Kind, DeserializableBytesStream[_ <: SerializableBytesStream]] = Map(
...
)

BytesStream.Kind is type for Enumeration.Value and each value at the map is object at the same package like:

sealed trait Foo extends SerializableBytesStream {
...
}

case class XXX(...) extends Foo {
...
 override val bytesStreamKind: BytesStream.Kind = BytesStream.Kinds.XXX
}

object XXX extends DeserializableBytesStream[XXX] {
 ....
 override val bytesStreamKind: BytesStream.Kind = BytesStream.Kinds.XXX
}

Yes, XXX is the same name of object and enum's value.

If the map has 20 or more elements, it is triggered infinity loop.