SI-6956 determine switchability by type, not tree

Constant folding will set the type of a constant tree
to `ConstantType(Constant(folded))`, while the tree
itself can be many different things (in casu, an Ident).

We used to look at the tree directly when deciding whether
to emit a switch. Now we look at the tree's type. Voilà.

2 files changed, 27 insertions, 0 deletions

diff --git a/test/files/run/t6956.check b/test/files/run/t6956.check
new file mode 100644
index 0000000000..0cfbf08886
--- /dev/null
+++ b/test/files/run/t6956.check
@@ -0,0 +1 @@
+2
diff --git a/test/files/run/t6956.scala b/test/files/run/t6956.scala
new file mode 100644
index 0000000000..4a6583ca45
--- /dev/null
+++ b/test/files/run/t6956.scala
@@ -0,0 +1,26 @@
+import scala.tools.partest.IcodeTest
+
+class Switches {
+  private[this] final val ONE = 1
+
+  def switchBad(i: Byte): Int = i match {
+    case ONE => 1
+    case 2 => 2
+    case 3 => 3
+    case _ => 0
+  }
+
+  def switchOkay(i: Byte): Int = i match {
+    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)
+}
+