Corrects behavior of finalResultType.

The implementation had come to depend on finalResultType
accidentally doing things beyond its charter - in particular,
widening types. After hunting down and fixing the call sites
depending on the bugs, I was able to rewrite the method to do
only what it's supposed to do.

I threw in a different way of writing it entirely to suggest how
some correctness might be obtained in the future. It's a lot
harder for a method written like this to break.

1 files changed, 49 insertions, 2 deletions

diff --git a/test/files/pos/infersingle.scala b/test/files/pos/infersingle.scala
index 6830fcd799..60f4ff07e6 100644
--- a/test/files/pos/infersingle.scala
+++ b/test/files/pos/infersingle.scala
@@ -1,5 +1,52 @@
-object Test {
+object Test1 {
   def one[T](x: T): Option[T] = Some(x)
   val x = "one"
   val y: Option[x.type] = one(x)
-}
\ No newline at end of file
+}
+
+object Test2 {
+  // Has never worked, but seems desirable given the recent changes to
+  // pattern type inference.
+  val a = ""
+  object Id {
+    def unapply(xxxx: Any): Some[a.type] = Some[a.type](a)
+  }
+  val b: a.type = (a: a.type) match {
+    case Id(x) => x
+  }
+}
+
+object Test3 {
+  val a = ""
+  object Id {
+    def unapply(xxxx: Any): Some[Test3.type] = Some[Test3.type](Test3)
+  }
+  val b: Test3.type = a match {
+    case Id(x) => x
+  }
+}
+
+class Test4 {
+  val a = ""
+  object Id {
+    def unapply(xxxx: Any): Some[Test4.this.type] = Some[Test4.this.type](Test4.this)
+  }
+  val b: Test4.this.type = a match {
+    case Id(x) => x
+  }
+}
+
+class Super5 {
+  final val q = ""
+  def q1: q.type = q
+}
+
+class Test5 extends Super5 {
+  val a = ""
+  object Id {
+    def unapply(xxxx: Any): Some[Test5.super.q.type] = Some[Test5.super.q.type](q1)
+  }
+  val b: Test5.super.q.type = a match {
+    case Id(x) => x
+  }
+}