Improves exhaustiveness analysis to not warn ab...

Improves exhaustiveness analysis to not warn about types which cannot
match due to nonconformant type parameters. Also, look at the different
warnings emitted in the test case based on the presence of a constraint.
Nifty! Closes #3683, no review.

7 files changed, 67 insertions, 3 deletions

diff --git a/test/files/neg/bug3683a.check b/test/files/neg/bug3683a.check
new file mode 100644
index 0000000000..a1c5b9c56d
--- /dev/null
+++ b/test/files/neg/bug3683a.check
@@ -0,0 +1,6 @@
+bug3683a.scala:14: error: match is not exhaustive!
+missing combination             XX
+
+    w match {
+    ^
+one error found
diff --git a/test/files/neg/bug3683a.flags b/test/files/neg/bug3683a.flags
new file mode 100644
index 0000000000..85d8eb2ba2
--- /dev/null
+++ b/test/files/neg/bug3683a.flags
@@ -0,0 +1 @@
+-Xfatal-warnings
diff --git a/test/files/neg/bug3683a.scala b/test/files/neg/bug3683a.scala
new file mode 100644
index 0000000000..6d1915213a
--- /dev/null
+++ b/test/files/neg/bug3683a.scala
@@ -0,0 +1,20 @@
+sealed trait Foo
+sealed trait Bar extends Foo
+sealed trait W[T >: Bar <: Foo]
+case class X() extends W[Foo]
+case class XX() extends W[Bar]
+case class Y() extends W[Bar]
+case class Z[T >: Bar <: Foo](
+  z1: W[T]
+) extends W[T]
+
+object Main {
+  // should warn for not including XX()
+  def f1(w: W[Bar]): Int = {
+    w match {
+      // case XX() => 2
+      case Y() => 1
+      case Z(z) => f1(z)
+    }
+  }
+}
\ No newline at end of file
diff --git a/test/files/neg/bug3683b.check b/test/files/neg/bug3683b.check
new file mode 100644
index 0000000000..3952633d1d
--- /dev/null
+++ b/test/files/neg/bug3683b.check
@@ -0,0 +1,6 @@
+bug3683b.scala:15: error: constructor cannot be instantiated to expected type;
+ found   : X
+ required: W[Bar]
+      case X() => 1
+           ^
+one error found
diff --git a/test/files/neg/bug3683b.scala b/test/files/neg/bug3683b.scala
new file mode 100644
index 0000000000..646e418121
--- /dev/null
+++ b/test/files/neg/bug3683b.scala
@@ -0,0 +1,21 @@
+sealed trait Foo
+sealed trait Bar extends Foo
+sealed trait W[T >: Bar <: Foo]
+case class X() extends W[Foo]
+case class XX() extends W[Bar]
+case class Y() extends W[Bar]
+case class Z[T >: Bar <: Foo](
+  z1: W[T]
+) extends W[T]
+
+object Main {
+  // should fail for including X()
+  def f1(w: W[Bar]): Int = {
+    w match {
+      case X() => 1
+      case XX() => 2
+      case Y() => 1
+      case Z(z) => f1(z)
+    }
+  }
+}
\ No newline at end of file
diff --git a/test/files/neg/exhausting.check b/test/files/neg/exhausting.check
index 6383a6eaca..d3f2251f79 100644
--- a/test/files/neg/exhausting.check
+++ b/test/files/neg/exhausting.check
@@ -14,11 +14,16 @@ missing combination           Bar3
   def fail3[T](x: Foo[T]) = x match {
                             ^
 exhausting.scala:31: error: match is not exhaustive!
+missing combination           Bar2          Bar2
+
+  def fail4[T <: AnyRef](xx: (Foo[T], Foo[T])) = xx match {
+      ^
+exhausting.scala:36: error: match is not exhaustive!
 missing combination           Bar1          Bar2
 missing combination           Bar1          Bar3
 missing combination           Bar2          Bar1
 missing combination           Bar2          Bar2
 
-  def fail4[T](xx: (Foo[T], Foo[T])) = xx match {
+  def fail5[T](xx: (Foo[T], Foo[T])) = xx match {
       ^
-four errors found
+5 errors found
diff --git a/test/files/neg/exhausting.scala b/test/files/neg/exhausting.scala
index 8b1ea817e4..0741d7467b 100644
--- a/test/files/neg/exhausting.scala
+++ b/test/files/neg/exhausting.scala
@@ -28,7 +28,12 @@ object Test {
     case Bar1   => "ok"
     case Bar2   => "ok"
   }
-  def fail4[T](xx: (Foo[T], Foo[T])) = xx match {
+  def fail4[T <: AnyRef](xx: (Foo[T], Foo[T])) = xx match {
+    case (Bar1, Bar1) => ()
+    case (Bar2, Bar3) => ()
+    case (Bar3, _) => ()
+  }
+  def fail5[T](xx: (Foo[T], Foo[T])) = xx match {
     case (Bar1, Bar1) => ()
     case (Bar2, Bar3) => ()
     case (Bar3, _) => ()