Fix ambiguity errors with polymorphic implicits

Previously, `isAsSpecific(alt1, tp1, alt2, tp2)` did not handle
having `tp2` be a polymorphic non-method type like `[A]Foo[A]`.

Also update the documentation of `isAsSpecific` to account for this
change, the new documentation is based on SLS § 6.26.3 but
adapted to reflect the code.

2 files changed, 15 insertions, 0 deletions

diff --git a/tests/run/implicits_poly.check b/tests/run/implicits_poly.check
new file mode 100644
index 000000000..0b148ee47
--- /dev/null
+++ b/tests/run/implicits_poly.check
@@ -0,0 +1 @@
+barFoo
diff --git a/tests/run/implicits_poly.scala b/tests/run/implicits_poly.scala
new file mode 100644
index 000000000..2a5d68f73
--- /dev/null
+++ b/tests/run/implicits_poly.scala
@@ -0,0 +1,14 @@
+class Foo[A](val x: String)
+class Bar[A](x: String) extends Foo[A](x)
+
+object Test {
+  implicit def anyRefFoo[A <: AnyRef]: Foo[A] = new Foo("anyRefFoo")
+  implicit def fooFoo[A]: Foo[Foo[A]] = new Foo("fooFoo")
+  implicit def barFoo[A]: Bar[Foo[A]] = new Bar("barFoo")
+
+  def getFooFoo(implicit ev: Foo[Foo[Int]]) = ev
+
+  def main(args: Array[String]): Unit = {
+    println(getFooFoo.x)
+  }
+}