From 9fa65772dafb274741b7b6f7a8a8082ddd4dea50 Mon Sep 17 00:00:00 2001
From: Jasper Moeys <jaspermoeys@hotmail.com>
Date: Mon, 30 Aug 2021 12:50:08 +0200
Subject: [PATCH] support AppliedType in outerTestNeeded

---
 .../tools/dotc/transform/PatternMatcher.scala | 11 +++++---
 tests/run/t13418.check                        |  3 +++
 tests/run/t13418.scala                        | 26 +++++++++++++++++++
 3 files changed, 36 insertions(+), 4 deletions(-)
 create mode 100644 tests/run/t13418.check
 create mode 100644 tests/run/t13418.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
index 536c566bfead..5a640c8f1d98 100644
--- a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
+++ b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
@@ -719,16 +719,19 @@ object PatternMatcher {
           val expectedTp = tpt.tpe
 
           // An outer test is needed in a situation like  `case x: y.Inner => ...`
-          def outerTestNeeded: Boolean =
-            // See the test for SI-7214 for motivation for dealias. Later `treeCondStrategy#outerTest`
-            // generates an outer test based on `patType.prefix` with automatically dealises.
-            expectedTp.dealias match {
+          def outerTestNeeded: Boolean = {
+            def go(expected: Type): Boolean = expected match {
               case tref @ TypeRef(pre: SingletonType, _) =>
                 tref.symbol.isClass &&
                 ExplicitOuter.needsOuterIfReferenced(tref.symbol.asClass)
+              case AppliedType(tpe, _) => go(tpe)
               case _ =>
                 false
             }
+            // See the test for SI-7214 for motivation for dealias. Later `treeCondStrategy#outerTest`
+            // generates an outer test based on `patType.prefix` with automatically dealises.
+            go(expectedTp.dealias)
+          }
 
           def outerTest: Tree = thisPhase.transformFollowingDeep {
             val expectedOuter = singleton(expectedTp.normalizedPrefix)
diff --git a/tests/run/t13418.check b/tests/run/t13418.check
new file mode 100644
index 000000000000..7614df8ec464
--- /dev/null
+++ b/tests/run/t13418.check
@@ -0,0 +1,3 @@
+ok
+ok
+ok
diff --git a/tests/run/t13418.scala b/tests/run/t13418.scala
new file mode 100644
index 000000000000..344bae8a274b
--- /dev/null
+++ b/tests/run/t13418.scala
@@ -0,0 +1,26 @@
+class A { class B }
+val a1 = new A
+val a2 = new A
+val b: Any = new a1.B
+
+class X { class Y[Q] }
+val x1 = new X
+val x2 = new X
+val y: Any = new x1.Y[Int]
+type Foo = [Q] =>> x2.Y[Q]
+type Bar = [Q] =>> x1.Y[Q]
+
+@main def Test() = {
+  b match {
+    case _: a2.B => println("wrong")
+    case _: a1.B => println("ok")
+  }
+  y match {
+    case _: x2.Y[_] => println("wrong")
+    case _: x1.Y[_] => println("ok")
+  }
+  y match {
+    case _: Foo[_] => println("wrong")
+    case _: Bar[_] => println("ok")
+  }
+}