Fix #1991: Use classtag where available in unapply

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/run/i1991.scala b/tests/run/i1991.scala
new file mode 100644
index 000000000..524a3f311
--- /dev/null
+++ b/tests/run/i1991.scala
@@ -0,0 +1,20 @@
+import scala.reflect.ClassTag
+
+class A[Foo](implicit tag: ClassTag[Foo]) {
+  object ExtractFoo {
+    def unapply(foo: Foo): Boolean = true
+  }
+
+  def isFoo(x: Any) = x match {
+    case ExtractFoo() => true
+    //case foo: Foo => true
+    case _ => false
+  }
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    assert((new A[String]).isFoo("foo")) // OK
+    assert(!(new A[String]).isFoo(42)) // OK in scalac, fails in Dotty
+  }
+}