1 files changed, 36 insertions, 0 deletions
diff --git a/test/files/run/t6900.scala b/test/files/run/t6900.scala
new file mode 100644
index 0000000000..a29d388129
--- /dev/null
+++ b/test/files/run/t6900.scala
@@ -0,0 +1,36 @@
+import annotation.tailrec
+
+trait Universe {
+  type T <: AnyRef
+}
+
+final class Bug {
+  var i = 1
+  def stop() = { i -= 1; i < 0 }
+  // the alias bypasses the fast path in erasures InfoTransformer
+  // predicated on `TypeMap.noChangeToSymbols`
+  type Alias = Any
+
+  @tailrec
+  // So we get two symbols for `universe`, the original on the ValDef
+  // and a clone in the MethodType of `f`.
+  def f(universe: Universe, l: Alias): universe.T = {
+    if (stop()) null.asInstanceOf[universe.T] else f(universe, null)
+  }
+
+  @tailrec
+  def g(universe: Universe)(l: Alias): universe.T = {
+    if (stop()) null.asInstanceOf[universe.T] else g(universe)(l)
+  }
+
+  @tailrec
+  def h(universe: Universe)(l: List[universe.T]): List[universe.T] = {
+    if (stop()) Nil else h(universe)(l)
+  }
+}
+
+object Test extends App {
+  assert(new Bug().f(null, null) == null)
+  assert(new Bug().g(null)(null) == null)
+  assert(new Bug().h(null)(null) == Nil)
+}
+\ No newline at end of file