Add a test for -Zirrefutable-generator-patterns

Author: puffnfresh

test/files/pos/Zirrefutable-generator-patterns.flags

@@ -0,0 +1 @@
+-Zirrefutable-generator-patterns

test/files/pos/Zirrefutable-generator-patterns.scala

@@ -0,0 +1,11 @@
+case class Foo[A](a: A) {
+  def map[B](f: A => B): Foo[B] = Foo(f(a))
+  def flatMap[B](f: A => Foo[B]): Foo[B] = Foo(f(a).a)
+}
+
+object Test {
+  for {
+    (a, b) <- Foo((1, 'd'))
+    (c, d, e) <- Foo((1, true, "three"))
+  } yield (a + c, e :+ b, !d)
+}