From 678e8e47b630786df7548c1be5bee744342f826c Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Sat, 28 Jan 2017 17:11:56 +1100
Subject: [PATCH] Disallow polymorphic refinements in stuctural types.

We can't handle them with the proposed scheme. I made a note in #1886.
---
 compiler/src/dotty/tools/dotc/typer/Typer.scala |  4 +++-
 tests/neg/structural.scala                      | 11 +++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 tests/neg/structural.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index ec4c135f74c2..48636c27c430 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -1039,7 +1039,9 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
     for (refinement <- refinements1) { // TODO: get clarity whether we want to enforce these conditions
       typr.println(s"adding refinement $refinement")
       checkRefinementNonCyclic(refinement, refineCls, seen)
-    }
+      val rsym = refinement.symbol
+      if (rsym.info.isInstanceOf[PolyType] && rsym.allOverriddenSymbols.isEmpty)
+        ctx.error(i"polymorphic refinement $rsym without matching type in parent $tpt1 is no longer allowed", refinement.pos)    }
     assignType(cpy.RefinedTypeTree(tree)(tpt1, refinements1), tpt1, refinements1, refineCls)
   }
 
diff --git a/tests/neg/structural.scala b/tests/neg/structural.scala
new file mode 100644
index 000000000000..aab52b2cb74d
--- /dev/null
+++ b/tests/neg/structural.scala
@@ -0,0 +1,11 @@
+object Test3 {
+  import scala.reflect.Selectable.reflectiveSelectable
+  def g(x: { type T ; def t: T ; def f(a: T): Boolean }) = x.f(x.t) // error: no ClassTag for x.T
+  g(new { type T = Int; def t = 4; def f(a:T) = true })
+  g(new { type T = Any; def t = 4; def f(a:T) = true })
+  val y: { type T = Int; def t = 4; def f(a:T) = true }
+    = new { type T = Int; def t = 4; def f(a:T) = true }
+
+  def h(x: { def f[T](a: T): Int }) = x.f[Int](4) // error: polymorphic refinement method ... no longer allowed
+
+}