Fix hole in scan for outer references

Type tests of singletons need to be considered as well.

Author: odersky

compiler/src/dotty/tools/dotc/transform/ExplicitOuter.scala

@@ -282,6 +282,9 @@ object ExplicitOuter {
       case TypeRef(prefix, _) => isOuterRef(prefix)
       case _ => false
     }
+    def containsOuterRefs(tp: Type): Boolean = tp match
+      case tp: SingletonType => isOuterRef(tp)
+      case tp: AndOrType => containsOuterRefs(tp.tp1) || containsOuterRefs(tp.tp2)
     tree match {
       case _: This | _: Ident => isOuterRef(tree.tpe)
       case nw: New =>
@@ -292,6 +295,9 @@ object ExplicitOuter {
           // newCls might get proxies for free variables. If current class is
           // properly contained in newCls, it needs an outer path to newCls access the
           // proxies and forward them to the new instance.
+      case app: TypeApply if app.symbol.isTypeTest =>
+        // Type tests of singletons translate to `eq` tests with references, which might require outer pointers
+        containsOuterRefs(app.args.head.tpe)
       case _ =>
         false
     }

compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala

@@ -295,7 +295,7 @@ object TypeTestsCasts {
             derivedTree(expr, defn.Any_asInstanceOf, testType)
         }
 
-        /** Transform isInstanceOf OrType
+        /** Transform isInstanceOf
          *
          *    expr.isInstanceOf[A | B]  ~~>  expr.isInstanceOf[A] | expr.isInstanceOf[B]
          *    expr.isInstanceOf[A & B]  ~~>  expr.isInstanceOf[A] & expr.isInstanceOf[B]

tests/pos/i12616.scala

@@ -0,0 +1,9 @@
+class Foo:
+
+  //object Bar
+  val Bar = 22
+
+  object Baz:
+    def f(x: Any): Unit =
+      x match
+        case s: (Bar.type & x.type) =>