From cd7951356808238cfb9545c2077d14a242e3bc20 Mon Sep 17 00:00:00 2001
From: Allan Renucci <allan.renucci@gmail.com>
Date: Wed, 3 Jan 2018 18:30:14 +0100
Subject: [PATCH] Fix #2840: Add regression test

---
 .../src/dotty/tools/dotc/transform/PatternMatcher.scala   | 2 +-
 tests/pickling/i2840.scala                                | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 tests/pickling/i2840.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
index 599c577dd2f0..d810ec420bb7 100644
--- a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
+++ b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
@@ -969,7 +969,7 @@ object PatternMatcher {
         }
         def numConsts(cdefs: List[CaseDef]): Int = {
           val tpes = cdefs.map(_.pat.tpe)
-          tpes.toSet.size: Int // without the type ascription, testPickling fails because of #2840.
+          tpes.toSet.size
         }
         if (numConsts(resultCases) < numConsts(original.cases))
           ctx.warning(UnableToEmitSwitch(), original.pos)
diff --git a/tests/pickling/i2840.scala b/tests/pickling/i2840.scala
new file mode 100644
index 000000000000..a2459c25eb2d
--- /dev/null
+++ b/tests/pickling/i2840.scala
@@ -0,0 +1,8 @@
+object Test {
+  class Type
+  def f(x: Type): Type = ???
+  def g(xs: List[Type]): Int = {
+    val ys = xs.map(f)
+    ys.toSet.size
+  }
+}