Merge pull request scala#9653 from dwijnand/fix-prefixAlign

Fix prefixAligns, avoid spurious outer test warnings on patdep types

Author: dwijnand

src/compiler/scala/tools/nsc/transform/patmat/MatchTreeMaking.scala

@@ -393,8 +393,9 @@ trait MatchTreeMaking extends MatchCodeGen with Debugging {
                   case TypeRef(pre, _, _) if !pre.isStable => // e.g. _: Outer#Inner
                     false
                   case TypeRef(pre, sym, args) =>
-                    val testedBinderClass = testedBinder.info.upperBound.typeSymbol
-                    // alternatively..... = testedBinder.info.baseClasses.find(_.isClass).getOrElse(NoSymbol)
+                    val testedBinderClass = testedBinder.info.baseClasses.find { sym =>
+                      sym.isClass && !sym.isRefinementClass
+                    }.getOrElse(NoSymbol)
                     val testedBinderType = testedBinder.info.baseType(testedBinderClass)
 
                     val testedPrefixIsExpectedTypePrefix = pre =:= testedBinderType.prefix

test/files/pos/t12392.scala

@@ -1,3 +1,4 @@
+// scalac: -Werror
 import scala.reflect.api.Universe
 
 object Test {

test/files/pos/t12398.scala

@@ -0,0 +1,11 @@
+// scalac: -Werror
+import scala.reflect.api.Universe
+
+object Test {
+  type SingletonUniverse = Universe with Singleton
+
+  def foo[U <: SingletonUniverse](u: U)(typ: u.Type): List[u.Annotation] = typ match {
+    case t: u.AnnotatedTypeApi => t.annotations // was: "The outer reference in this type test cannot be checked at run time."
+    case _                     => Nil
+  }
+}

test/files/pos/t12398b.scala

@@ -0,0 +1,11 @@
+// scalac: -Werror
+import scala.reflect.api.Universe
+
+object Test {
+  type SingletonUniverse = Universe with Singleton
+
+  def foo[U <: SingletonUniverse](u: U)(typ: U#Type): List[U#Annotation] = typ match {
+    case t: U#AnnotatedTypeApi => t.annotations // as a comparison, this wasn't emitting a warning
+    case _                     => Nil
+  }
+}