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.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala b/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
index d8cfd5a765..454d9210ff 100644
--- a/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
@@ -3494,8 +3494,10 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
       val alternativesSupported = true
       val canJump = true
 
-      object SwitchablePattern { def unapply(pat: Tree): Option[Tree] = pat match {
-        case Literal(const@Constant((_: Byte ) | (_: Short) | (_: Int  ) | (_: Char ))) =>
+      // Constant folding sets the type of a constant tree to `ConstantType(Constant(folded))`
+      // The tree itself can be a literal, an ident, a selection, ...
+      object SwitchablePattern { def unapply(pat: Tree): Option[Tree] = pat.tpe match {
+        case ConstantType(const@Constant((_: Byte ) | (_: Short) | (_: Int  ) | (_: Char ))) =>
           Some(Literal(Constant(const.intValue))) // TODO: Java 7 allows strings in switches
         case _ => None
       }}