Incremental compiler fails when type parameter in trait is inferred

[Anghammar]

Compiler version

3.6.3

Minimized code

File 1:

object IncrementalCompilerBug {
  import IncrementalCompilerBugOtherFile.Foo
  val x: Foo.InnerTrait = Foo.ExplicitTypeParameter
  val y: Foo.InnerTrait = Foo.TypeParameterFromInference
}

File 2:

object IncrementalCompilerBugOtherFile {
  trait SuperTrait {
    trait InnerTrait
    trait TraitWithTypeParameter[A](a: A) extends InnerTrait
  }
  object Foo extends SuperTrait {
    object ExplicitTypeParameter extends TraitWithTypeParameter[Int](3)
    object TypeParameterFromInference extends TraitWithTypeParameter(3)
  }
}

Output

Found:    IncrementalCompilerBugOtherFile.Foo.TypeParameterFromInference.type
Required: IncrementalCompilerBugOtherFile.Foo.InnerTrait [4:27]

Expectation

File 1 and 2 compiles just fine when you compile them both, e.g. when doing clean and compile in SBT. However, doing any irrelevant change in file 1 (like adding a comment or whitespace) without touching file 2 and recompiling with SBT will result in the compilation failure above at val y since TypeParameterFromInference extends TraitWithTypeParameter using type inference. In comparison, the compiler never have any problem with val x.

[Gedochao]

I managed to reproduce it with SBT, but it doesn't occur with Scala CLI.
Seems to be SBT-specific.

[Gedochao]

@adpi2 any clue?

[som-snytt]

It reproduces for me with separate compilation (second file first).

➜  i22651 ~/projects/dotty/bin/scalacQ -d ~/sandbox b.scala
➜  i22651 ~/projects/dotty/bin/scalacQ -d ~/sandbox -cp ~/sandbox a.scala
-- [E007] Type Mismatch Error: a.scala:5:30 ------------------------------------
5 |  val y: Foo.InnerTrait = Foo.TypeParameterFromInference
  |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |Found:    IncrementalCompilerBugOtherFile.Foo.TypeParameterFromInference.type
  |Required: IncrementalCompilerBugOtherFile.Foo.InnerTrait
  |
  | longer explanation available when compiling with `-explain`
1 error found
➜  i22651