From 8f7fd96fb343ba41a77cc13114e04beef41724ba Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Thu, 27 May 2021 10:52:55 +0200
Subject: [PATCH] Fix hole in scan for outer references

Type tests of singletons need to be considered as well.
---
 .../src/dotty/tools/dotc/transform/ExplicitOuter.scala   | 7 +++++++
 .../src/dotty/tools/dotc/transform/TypeTestsCasts.scala  | 2 +-
 tests/pos/i12616.scala                                   | 9 +++++++++
 3 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/i12616.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/ExplicitOuter.scala b/compiler/src/dotty/tools/dotc/transform/ExplicitOuter.scala
index 8b13633e6125..7a211631a481 100644
--- a/compiler/src/dotty/tools/dotc/transform/ExplicitOuter.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ExplicitOuter.scala
@@ -282,6 +282,10 @@ 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)
+      case _ => false
     tree match {
       case _: This | _: Ident => isOuterRef(tree.tpe)
       case nw: New =>
@@ -292,6 +296,9 @@ 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
     }
diff --git a/compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala b/compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala
index 2679fbeaf94d..894bbc433dca 100644
--- a/compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala
+++ b/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]
diff --git a/tests/pos/i12616.scala b/tests/pos/i12616.scala
new file mode 100644
index 000000000000..ff5a6bf204fd
--- /dev/null
+++ 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) =>
\ No newline at end of file