dotty-doc-bootstrapped can't be compiled with -Ycheck:all

[gsps]

In the current build dotty-doc is not compiled with any -Ychecks, but if ones does, e.g., by adding scalacOptions ++= "-Ycheck:all" to dottyDocSettings in Build.scala, then the bootstrapped compiler fails as follows:

[error] (dotty-doc-bootstrapped/compile:compileIncremental) java.lang.AssertionError: assertion failed: Types differ
[error] Original type : Map[String, Nothing]
[error] After checking: Map[String, Any]
[error] Original tree : Map.empty[String, Any]
[error] After checking: Map.empty[String, Any]
[error] Why different :
[error]              Subtype trace:
[error]   ==> Map[String, Any] <:< Map[String, Nothing]
[error]     ==> compareAppliedType2 Map[String, Any], Map[String, Nothing]
[error]       ==> scala.collection.immutable.type(scala.collection.immutable) <:< scala.collection.immutable.type(scala.collection.immutable)
[error]       <== scala.collection.immutable.type(scala.collection.immutable) <:< scala.collection.immutable.type(scala.collection.immutable) = true
[error]       ==> String <:< String
[error]         ==> String <:< String
[error]         <== String <:< String = true
[error]       <== String <:< String = true
[error]       ==> String <:< String
[error]         ==> String <:< String
[error]           ==> String <:< String
[error]             ==> String <:< String
[error]             <== String <:< String = true
[error]           <== String <:< String = true
[error]         <== String <:< String = true
[error]       <== String <:< String = true
[error]       ==> Any <:< Nothing
[error]         ==> Any <:< Nothing
[error]         <== Any <:< Nothing = false
[error]       <== Any <:< Nothing = false
[error]       ==> compareAppliedType1 Map[String, Any], Map[String, Nothing]
[error]       <== compareAppliedType1 Map[String, Any], Map[String, Nothing] = false
[error]     <== compareAppliedType2 Map[String, Any], Map[String, Nothing] = false
[error]   <== Map[String, Any] <:< Map[String, Nothing] = false

The culprit here is the Map.empty in

implicit class OptMap(val opt: Option[JMap[String, _]]) extends AnyVal {
  def asJava = opt.getOrElse(Map.empty.asJava)
}

found in JavaConverters.scala.

One can work around the problem by adding a type parameter to OptMap[V] and instantiating the types in Map.empty[String, V] explicitly, but I suppose the Checker should be adapted.

[smarter]

Could you make a minimal example reproducing the problem? Also can you check if it happens on top of #4183 ?

[gsps]

Given that #4183 has been merged, I'll try again once I've rebased my branch on top of master.

[OlivierBlanvillain]

Seams to be fixed on master