Add support for Polytypes (#79)

* Add PolyType to TPrintImpl

* Add TPrint test for polytype

* Tweak based on PR feedback

* Allow Polytypes to be different on 2.12 vs 2.13

Author: valencik

pprint/src-2/TPrintImpl.scala

@@ -221,6 +221,12 @@ object TPrintLowPri{
             .map(typePrintImplRec(c)(_, true))
             .reduceLeft[fansi.Str]((l, r) => l  ++ " with " ++ r)
         (pre + (if (defs.isEmpty) "" else "{" ++ defs.mkString(";") ++ "}"), WrapType.NoWrap)
+      case PolyType(typeParams, resultType) =>
+        val params = printArgSyms(typeParams)
+        (
+          params ++ typePrintImplRec(c)(resultType, true),
+          WrapType.NoWrap
+        )
       case ConstantType(value) =>
         val pprintedValue =
           pprint.PPrinter.BlackWhite.copy(colorLiteral = fansi.Color.Green).apply(value.value)

pprint/test/src-2/test/pprint/TPrintTests.scala

@@ -235,6 +235,22 @@ object TPrintTests extends TestSuite{
       import scala.reflect.runtime.universe._
       check[Nothing]("Nothing")
     }
+    test("polytype"){
+      import scala.language.implicitConversions
+      type Foo[+A] = Unit
+      trait Bar[F[_], A]
+      object Bar {
+        implicit def anyToBar[A](a: A): Bar[Foo, A] = new Bar[Foo, A] {}
+        def apply[F[_], A](b: Bar[F, A]): Bar[F, A] = b
+      }
+      object Print {
+        def tprint[A](a: A)(implicit t: pprint.TPrint[A]) = t.render
+      }
+      val rendered = Print.tprint(Bar(1)).toString()
+
+      val is213Plus = classOf[Seq[Int]].getName != "scala.collection.Seq"
+      assert(rendered == (if (is213Plus) "Bar[[A]Foo[A], Int]" else "Bar[Foo, Int]"))
+    }
   }
 }