Fix t10100: add test

Author: liufengyun

tests/patmat/t10100.check

@@ -0,0 +1 @@
+12: Pattern Match Exhaustivity: (_, FancyFoo(_))

tests/patmat/t10100.scala

@@ -0,0 +1,27 @@
+sealed trait Foo {
+  val index: Int
+}
+
+case class BasicFoo(index: Int) extends Foo
+
+class NonExhaustive {
+  case class FancyFoo(index: Int) extends Foo
+
+  def convert(foos: Vector[Foo]): Vector[Int] = {
+    foos.foldLeft(Vector.empty[Int]) {
+      case (acc, basic: BasicFoo) => acc :+ basic.index
+      case (acc, fancy: FancyFoo) => acc :+ fancy.index
+    }
+  }
+}
+
+@main
+def Test = {
+  val a = new NonExhaustive
+  val b = new NonExhaustive
+
+  val fa: Foo = a.FancyFoo(3)
+  val fb: Foo = b.FancyFoo(4)
+
+  a.convert(Vector(fa, fb))
+}