chore: Consider source code as Scala 2 under -Ycompile-scala2-library

Author: hamzaremmal

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -246,7 +246,9 @@ class Namer { typer: Typer =>
 
     tree match {
       case tree: TypeDef if tree.isClassDef =>
-        val flags = checkFlags(tree.mods.flags)
+        var flags = checkFlags(tree.mods.flags)
+        if ctx.settings.YcompileScala2Library.value then
+          flags |= Scala2x
         val name = checkNoConflict(tree.name, flags.is(Private), tree.span).asTypeName
         val cls =
           createOrRefine[ClassSymbol](tree, name, flags, ctx.owner,

project/Scala2LibraryBootstrappedMiMaFilters.scala

@@ -69,17 +69,10 @@ object Scala2LibraryBootstrappedMiMaFilters {
         ProblemFilters.exclude[FinalMethodProblem]("scala.io.Source.NoPositioner"),
         ProblemFilters.exclude[FinalMethodProblem]("scala.io.Source.RelaxedPosition"),
         ProblemFilters.exclude[FinalMethodProblem]("scala.io.Source.RelaxedPositioner"),
-        ProblemFilters.exclude[IncompatibleResultTypeProblem]("scala.collection.immutable.SortedMapOps.coll"),
-        ProblemFilters.exclude[IncompatibleResultTypeProblem]("scala.collection.immutable.TreeMap.empty"),
-        ProblemFilters.exclude[IncompatibleResultTypeProblem]("scala.collection.immutable.TreeMap.fromSpecific"),
-        ProblemFilters.exclude[IncompatibleResultTypeProblem]("scala.collection.mutable.ArrayBuilder#ofUnit.addAll"),
-        ProblemFilters.exclude[IncompatibleResultTypeProblem]("scala.collection.mutable.TreeMap.empty"),
-        ProblemFilters.exclude[IncompatibleResultTypeProblem]("scala.collection.mutable.TreeMap.fromSpecific"),
         ProblemFilters.exclude[IncompatibleResultTypeProblem]("scala.reflect.ManifestFactory#NothingManifest.newArray"),
         ProblemFilters.exclude[IncompatibleResultTypeProblem]("scala.reflect.ManifestFactory#NullManifest.newArray"),
         ProblemFilters.exclude[MissingFieldProblem]("scala.collection.ArrayOps#ReverseIterator.xs"),
         ProblemFilters.exclude[MissingFieldProblem]("scala.runtime.NonLocalReturnControl.value"),
-        ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.collection.immutable.SortedMapOps.coll"),
       ) ++
       Seq( // DirectMissingMethodProblem
         "scala.collection.LinearSeqIterator#LazyCell.this",