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.

3 files changed, 152 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
+  }
+}
diff --git a/test/files/pos/private-types-after-typer.scala b/test/files/pos/private-types-after-typer.scala
new file mode 100644
index 0000000000..79ef934063
--- /dev/null
+++ b/test/files/pos/private-types-after-typer.scala
@@ -0,0 +1,9 @@
+// Testing that the type of the outer accessor in O2
+// doesn't crash the compiler over private type escaping scope.
+trait T {
+  class C {
+     private object O1 {
+        object O2
+     }
+  }
+}
\ No newline at end of file
diff --git a/test/files/run/compiler-asSeenFrom.check b/test/files/run/compiler-asSeenFrom.check
index 47d40b0331..7305504115 100644
--- a/test/files/run/compiler-asSeenFrom.check
+++ b/test/files/run/compiler-asSeenFrom.check
@@ -1,6 +1,54 @@
 class C {
   type                       seen from prefix           is
   ----                       ----------------           --
+  C.this.I[Int]              C[List[T3]]                C[List[T3]]#I[Int]
+  C.this.I[Int]              C[T1]                      C[T1]#I[Int]
+  C.this.I[Int]              D[A1]                      D[A1]#I[Int]
+  C.this.I[Int]              D[T3]                      D[T3]#I[Int]
+  C.this.I[List[Int]]        C[List[T3]]                C[List[T3]]#I[List[Int]]
+  C.this.I[List[Int]]        C[T1]                      C[T1]#I[List[Int]]
+  C.this.I[List[Int]]        D[A1]                      D[A1]#I[List[Int]]
+  C.this.I[List[Int]]        D[T3]                      D[T3]#I[List[Int]]
+  C.this.I[T1]               C[List[T3]]                C[List[T3]]#I[List[T3]]
+  C.this.I[T1]               C[T1]                      C[T1]#I[T1]
+  C.this.I[T1]               D[A1]                      D[A1]#I[A1]
+  C.this.I[T1]               D[T3]                      D[T3]#I[T3]
+  C.this.I[T2]               C[List[T3]]                C[List[T3]]#I[T2]
+  C.this.I[T2]               C[T1]                      C[T1]#I[T2]
+  C.this.I[T2]               D[A1]                      D[A1]#I[T2]
+  C.this.I[T2]               D[T3]                      D[T3]#I[T2]
+  C.this.I[T3]               C[List[T3]]                C[List[T3]]#I[T3]
+  C.this.I[T3]               C[T1]                      C[T1]#I[T3]
+  C.this.I[T3]               D[A1]                      D[A1]#I[T3]
+  C.this.I[T3]               D[T3]                      D[T3]#I[T3]
+  C.this.I[T4]               C[List[T3]]                C[List[T3]]#I[T4]
+  C.this.I[T4]               C[T1]                      C[T1]#I[T4]
+  C.this.I[T4]               D[A1]                      D[A1]#I[T4]
+  C.this.I[T4]               D[T3]                      D[T3]#I[T4]
+  C.this.J[Int]              C[List[T3]]                C[List[T3]]#J[Int]
+  C.this.J[Int]              C[T1]                      C[T1]#J[Int]
+  C.this.J[Int]              D[A1]                      D[A1]#J[Int]
+  C.this.J[Int]              D[T3]                      D[T3]#J[Int]
+  C.this.J[List[Int]]        C[List[T3]]                C[List[T3]]#J[List[Int]]
+  C.this.J[List[Int]]        C[T1]                      C[T1]#J[List[Int]]
+  C.this.J[List[Int]]        D[A1]                      D[A1]#J[List[Int]]
+  C.this.J[List[Int]]        D[T3]                      D[T3]#J[List[Int]]
+  C.this.J[T1]               C[List[T3]]                C[List[T3]]#J[List[T3]]
+  C.this.J[T1]               C[T1]                      C[T1]#J[T1]
+  C.this.J[T1]               D[A1]                      D[A1]#J[A1]
+  C.this.J[T1]               D[T3]                      D[T3]#J[T3]
+  C.this.J[T2]               C[List[T3]]                C[List[T3]]#J[T2]
+  C.this.J[T2]               C[T1]                      C[T1]#J[T2]
+  C.this.J[T2]               D[A1]                      D[A1]#J[T2]
+  C.this.J[T2]               D[T3]                      D[T3]#J[T2]
+  C.this.J[T3]               C[List[T3]]                C[List[T3]]#J[T3]
+  C.this.J[T3]               C[T1]                      C[T1]#J[T3]
+  C.this.J[T3]               D[A1]                      D[A1]#J[T3]
+  C.this.J[T3]               D[T3]                      D[T3]#J[T3]
+  C.this.J[T4]               C[List[T3]]                C[List[T3]]#J[T4]
+  C.this.J[T4]               C[T1]                      C[T1]#J[T4]
+  C.this.J[T4]               D[A1]                      D[A1]#J[T4]
+  C.this.J[T4]               D[T3]                      D[T3]#J[T4]
   C[List[T3]]#I[T1]          D[A1]                      C[List[T3]]#I[A1]
   C[List[T3]]#I[T1]          D[T3]                      C[List[T3]]#I[T3]
   C[List[T3]]#J[T1]          D[A1]                      C[List[T3]]#J[A1]
@@ -49,6 +97,8 @@ class C {
 class D {
   type                       seen from prefix           is
   ----                       ----------------           --
+  C.this.I[T3]               D[A1]                      C.this.I[A1]
+  C.this.J[T3]               D[A1]                      C.this.J[A1]
   C[List[T3]]#I[Int]         D[A1]                      C[List[A1]]#I[Int]
   C[List[T3]]#I[List[Int]]   D[A1]                      C[List[A1]]#I[List[Int]]
   C[List[T3]]#I[T1]          D[A1]                      C[List[A1]]#I[T1]
@@ -73,6 +123,42 @@ class D {
 class I {
   type                       seen from prefix           is
   ----                       ----------------           --
+  C.this.I[Int]              D.this.J[T4]               D.this.cD.I[Int]
+  C.this.I[Int]              Z.dZ.J[A2]                 Z.dZ.cD.I[Int]
+  C.this.I[Int]              Z.dZ.J[P]                  Z.dZ.cD.I[Int]
+  C.this.I[List[Int]]        D.this.J[T4]               D.this.cD.I[List[Int]]
+  C.this.I[List[Int]]        Z.dZ.J[A2]                 Z.dZ.cD.I[List[Int]]
+  C.this.I[List[Int]]        Z.dZ.J[P]                  Z.dZ.cD.I[List[Int]]
+  C.this.I[T1]               D.this.J[T4]               D.this.cD.I[List[T3]]
+  C.this.I[T1]               Z.dZ.J[A2]                 Z.dZ.cD.I[List[A1]]
+  C.this.I[T1]               Z.dZ.J[P]                  Z.dZ.cD.I[List[A1]]
+  C.this.I[T2]               D.this.J[T4]               D.this.cD.I[T4]
+  C.this.I[T2]               Z.dZ.J[A2]                 Z.dZ.cD.I[A2]
+  C.this.I[T2]               Z.dZ.J[P]                  Z.dZ.cD.I[P]
+  C.this.I[T3]               D.this.J[T4]               D.this.cD.I[T3]
+  C.this.I[T3]               Z.dZ.J[A2]                 Z.dZ.cD.I[T3]
+  C.this.I[T3]               Z.dZ.J[P]                  Z.dZ.cD.I[T3]
+  C.this.I[T4]               D.this.J[T4]               D.this.cD.I[T4]
+  C.this.I[T4]               Z.dZ.J[A2]                 Z.dZ.cD.I[T4]
+  C.this.I[T4]               Z.dZ.J[P]                  Z.dZ.cD.I[T4]
+  C.this.J[Int]              D.this.J[T4]               D.this.cD.J[Int]
+  C.this.J[Int]              Z.dZ.J[A2]                 Z.dZ.cD.J[Int]
+  C.this.J[Int]              Z.dZ.J[P]                  Z.dZ.cD.J[Int]
+  C.this.J[List[Int]]        D.this.J[T4]               D.this.cD.J[List[Int]]
+  C.this.J[List[Int]]        Z.dZ.J[A2]                 Z.dZ.cD.J[List[Int]]
+  C.this.J[List[Int]]        Z.dZ.J[P]                  Z.dZ.cD.J[List[Int]]
+  C.this.J[T1]               D.this.J[T4]               D.this.cD.J[List[T3]]
+  C.this.J[T1]               Z.dZ.J[A2]                 Z.dZ.cD.J[List[A1]]
+  C.this.J[T1]               Z.dZ.J[P]                  Z.dZ.cD.J[List[A1]]
+  C.this.J[T2]               D.this.J[T4]               D.this.cD.J[T4]
+  C.this.J[T2]               Z.dZ.J[A2]                 Z.dZ.cD.J[A2]
+  C.this.J[T2]               Z.dZ.J[P]                  Z.dZ.cD.J[P]
+  C.this.J[T3]               D.this.J[T4]               D.this.cD.J[T3]
+  C.this.J[T3]               Z.dZ.J[A2]                 Z.dZ.cD.J[T3]
+  C.this.J[T3]               Z.dZ.J[P]                  Z.dZ.cD.J[T3]
+  C.this.J[T4]               D.this.J[T4]               D.this.cD.J[T4]
+  C.this.J[T4]               Z.dZ.J[A2]                 Z.dZ.cD.J[T4]
+  C.this.J[T4]               Z.dZ.J[P]                  Z.dZ.cD.J[T4]
   C[List[T3]]#I[T1]          D.this.J[T4]               C[List[T3]]#I[List[T3]]
   C[List[T3]]#I[T1]          Z.dZ.J[A2]                 C[List[T3]]#I[List[A1]]
   C[List[T3]]#I[T1]          Z.dZ.J[P]                  C[List[T3]]#I[List[A1]]
@@ -137,6 +223,14 @@ class I {
 class J {
   type                       seen from prefix           is
   ----                       ----------------           --
+  C.this.I[T3]               Z.dZ.J[A2]                 C.this.I[A1]
+  C.this.I[T3]               Z.dZ.J[P]                  C.this.I[A1]
+  C.this.I[T4]               Z.dZ.J[A2]                 C.this.I[A2]
+  C.this.I[T4]               Z.dZ.J[P]                  C.this.I[P]
+  C.this.J[T3]               Z.dZ.J[A2]                 C.this.J[A1]
+  C.this.J[T3]               Z.dZ.J[P]                  C.this.J[A1]
+  C.this.J[T4]               Z.dZ.J[A2]                 C.this.J[A2]
+  C.this.J[T4]               Z.dZ.J[P]                  C.this.J[P]
   C[List[T3]]#I[Int]         Z.dZ.J[A2]                 C[List[A1]]#I[Int]
   C[List[T3]]#I[Int]         Z.dZ.J[P]                  C[List[A1]]#I[Int]
   C[List[T3]]#I[List[Int]]   Z.dZ.J[A2]                 C[List[A1]]#I[List[Int]]