Fix #938

src/dotty/tools/dotc/core/Phases.scala

@@ -7,6 +7,7 @@ import dotty.tools.backend.jvm.{LabelDefs, GenBCode}
 import util.DotClass
 import DenotTransformers._
 import Denotations._
+import Decorators._
 import config.Printers._
 import scala.collection.mutable.{ListBuffer, ArrayBuffer}
 import dotty.tools.dotc.transform.TreeTransforms.{TreeTransformer, MiniPhase, TreeTransform}
@@ -121,10 +122,9 @@ object Phases {
               phase
             }
           squashedPhases += phaseToAdd
-          val shouldAddYCheck = YCheckAfter.exists(nm => phaseToAdd.phaseName.contains(nm)) || YCheckAll
+          val shouldAddYCheck = YCheckAfter.containsPhase(phaseToAdd) || YCheckAll
           if (shouldAddYCheck) {
             val checker = new TreeChecker
-
             squashedPhases += checker
           }
         }

src/dotty/tools/dotc/core/TypeComparer.scala

@@ -488,6 +488,9 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
         case _ => tp2 isRef ObjectClass
       }
       compareJavaArray
+    case tp1: ExprType if ctx.phase.id > ctx.gettersPhase.id =>
+      // getters might have converted T to => T, need to compensate.
+      isSubType(tp1.widenExpr, tp2)
     case _ =>
       false
   }

src/dotty/tools/dotc/typer/TypeAssigner.scala

@@ -46,10 +46,9 @@ trait TypeAssigner {
         // TODO: measure the cost of using `existsPart`, and if necessary replace it
         // by a `TypeAccumulator` where we have set `stopAtStatic = true`.
         tp existsPart {
-          case tp: NamedType =>
-            forbidden contains tp.symbol
-          case _ =>
-            false
+          case tp: NamedType => forbidden contains tp.symbol
+          case tp: ThisType => forbidden contains tp.cls
+          case _ => false
         }
       def apply(tp: Type): Type = tp match {
         case tp: TermRef if toAvoid(tp) && variance > 0 =>

test/dotc/scala-collections.whitelist

@@ -186,7 +186,7 @@
 ./scala-scala/src/library/scala/collection/SortedSetLike.scala
 ./scala-scala/src/library/scala/collection/Traversable.scala
 
-# https://github.com/lampepfl/dotty/issues/938
+# https://github.com/lampepfl/dotty/issues/938 (but relies also on #937 being fixed)
 #./scala-scala/src/library/scala/collection/TraversableLike.scala
 
 ./scala-scala/src/library/scala/collection/TraversableProxy.scala

tests/pos/i938.scala

@@ -0,0 +1,21 @@
+object Test {
+  import scala.collection._
+
+  trait T {
+    def f() : Unit
+  }
+
+  def view = new T {
+    def f() = ()
+  }
+
+  trait TLike[+A, RR] { self =>
+
+    def repr: RR = ???
+
+    def view2 = new TraversableView[A, RR] {
+      protected lazy val underlying = self.repr
+      override def foreach[U](f: A => U): Unit = ???
+    }
+  }
+}