Adding a new case to subtype tests.

This one handles situations like

  val sym: Symbol
  sym.type <:< Symbol { type ThisType = sym.ThisType }

1 files changed, 19 insertions, 8 deletions

diff --git a/src/dotty/tools/dotc/core/TypeComparer.scala b/src/dotty/tools/dotc/core/TypeComparer.scala
index 0d76155f1..5dbfc894d 100644
--- a/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -292,14 +292,25 @@ class TypeComparer(initctx: Context) extends DotClass {
           // optimized case; all info on tp1.name2 is in refinement tp1.refinedInfo.
           isSubType(tp1, parent2) && isSubType(tp1.refinedInfo, tp2.refinedInfo)
         case _ =>
-          def hasMatchingMember(name: Name): Boolean = traceIndented(s"hasMatchingMember($name)") {
-            tp1.member(name).hasAltWith(alt => isSubType(alt.info, tp2.refinedInfo)) ||
-            name.isHkParamName && {
-              val idx = name.hkParamIndex
-              val tparams = tp1.typeParams
-              idx < tparams.length && hasMatchingMember(tparams(idx).name)
-            }
-          }
+          def hasMatchingMember(name: Name): Boolean = traceIndented(s"hasMatchingMember($name)") (
+               tp1.member(name).hasAltWith(alt => isSubType(alt.info, tp2.refinedInfo))
+            ||
+               { // special case for situations like:
+                 //    foo <: C { type T = foo.T }
+                 tp2.refinedInfo match {
+                   case TypeBounds(lo, hi) if lo eq hi =>
+                     val ref = tp1 select name
+                     isSubType(ref, lo) && isSubType(hi, ref)
+                   case _ => false
+                 }
+               }
+            ||
+               name.isHkParamName && {
+                 val idx = name.hkParamIndex
+                 val tparams = tp1.typeParams
+                 idx < tparams.length && hasMatchingMember(tparams(idx).name)
+               }
+          )
           isSubType(tp1, parent2) && (
                name2 == nme.WILDCARD
             || hasMatchingMember(name2)