closes #3373, #3177: validity check of an impli...

closes #3373, #3177: validity check of an implicit value should consider
the value as well as its accessor review by odersky

1 files changed, 39 insertions, 0 deletions

diff --git a/test/files/pos/t3177.scala b/test/files/pos/t3177.scala
new file mode 100644
index 0000000000..9f9528faec
--- /dev/null
+++ b/test/files/pos/t3177.scala
@@ -0,0 +1,39 @@
+trait InvariantFunctor[F[_]] {
+  def xmap[A, B](ma: F[A], f: A => B, g: B => A): F[B]
+}
+
+object InvariantFunctor {
+  import Endo._
+
+  implicit val EndoInvariantFunctor = new InvariantFunctor[Endo] {
+    def xmap[A, B](ma: Endo[A], f: A => B, g: B => A): Endo[B] = (b: B) => f(ma(g(b)))
+  }
+
+  // The definition about fails with:
+  // anon-type.scala:9: error: not found: value b
+  //       def xmap[A, B](ma: Endo[A], f: A => B, g: B => A): Endo[B] = (b: B) => f(ma(g(b)))
+  //                                                                                     ^
+  //   anon-type.scala:8: error: not found: type $anon
+  //     implicit val EndoInvariantFunctor = new InvariantFunctor[Endo] {
+  //                                         ^
+
+
+  // These both work:
+  // implicit val EndoInvariantFunctorAscribed: InvariantFunctor[Endo] = new InvariantFunctor[Endo] {
+  //   def xmap[A, B](ma: Endo[A], f: A => B, g: B => A): Endo[B] = (b: B) => f(ma(g(b)))
+  // }
+  //
+  // implicit val EndoInvariantFunctorStubbed = new InvariantFunctor[Endo] {
+  //   def xmap[A, B](ma: Endo[A], f: A => B, g: B => A): Endo[B] = error("stub")
+  // }
+}
+
+trait Endo[X]
+
+object Endo {
+  implicit def EndoTo[A](f: A => A): Endo[A] = new Endo[A] {
+    def apply(a: A) = f(a)
+  }
+
+  implicit def EndoFrom[A](e: Endo[A]): A => A = e.apply(_)
+}
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