Merge pull request #1879 from adriaanm/ticket-6955

SI-6955 switch emission no longer foiled by type alias

3 files changed, 28 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala b/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
index d73fb680f2..d8cfd5a765 100644
--- a/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
@@ -3522,7 +3522,7 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
     override def emitSwitch(scrut: Tree, scrutSym: Symbol, cases: List[List[TreeMaker]], pt: Type, matchFailGenOverride: Option[Tree => Tree], unchecked: Boolean): Option[Tree] = { import CODE._
       val regularSwitchMaker = new RegularSwitchMaker(scrutSym, matchFailGenOverride, unchecked)
       // TODO: if patterns allow switch but the type of the scrutinee doesn't, cast (type-test) the scrutinee to the corresponding switchable type and switch on the result
-      if (regularSwitchMaker.switchableTpe(scrutSym.tpe)) {
+      if (regularSwitchMaker.switchableTpe(scrutSym.tpe.dealias)) { // TODO: switch to dealiasWiden in 2.11
         val caseDefsWithDefault = regularSwitchMaker(cases map {c => (scrutSym, c)}, pt)
         if (caseDefsWithDefault isEmpty) None // not worth emitting a switch.
         else {
diff --git a/test/files/run/t6955.check b/test/files/run/t6955.check
new file mode 100644
index 0000000000..0cfbf08886
--- /dev/null
+++ b/test/files/run/t6955.check
@@ -0,0 +1 @@
+2
diff --git a/test/files/run/t6955.scala b/test/files/run/t6955.scala
new file mode 100644
index 0000000000..2610acdec4
--- /dev/null
+++ b/test/files/run/t6955.scala
@@ -0,0 +1,26 @@
+import scala.tools.partest.IcodeTest
+
+class Switches {
+  type Tag = Byte
+
+  def switchBad(i: Tag): Int = i match { // notice type of i is Tag = Byte
+    case 1 => 1
+    case 2 => 2
+    case 3 => 3
+    case _ => 0
+  }
+
+  def switchOkay(i: Byte): Int = i match { // notice type of i is Byte
+    case 1 => 1
+    case 2 => 2
+    case 3 => 3
+    case _ => 0
+  }
+}
+
+object Test extends IcodeTest {
+  // ensure we get two switches out of this -- ignore the rest of the output for robustness
+  // exclude the constant we emit for the "SWITCH ..." string below (we get the icode for all the code you see in this file)
+  override def show() = println(collectIcode("").filter(x => x.indexOf("SWITCH ...") >= 0 && x.indexOf("CONSTANT(") == -1).size)
+}
+