Fix #1258: correct behavior for annotated values

Annotated values are encapsulated in a `ConcreteAnnotation`, as such,
the statement `tpe isRef defn.IntClass` would yield false despite the
annotated reference being an Int.

The tpe is now unwrapped if it has an annotation. If the transformation
fails despite having the annotation the compiler will warn.

1 files changed, 13 insertions, 5 deletions

diff --git a/src/dotty/tools/dotc/transform/PatternMatcher.scala b/src/dotty/tools/dotc/transform/PatternMatcher.scala
index 740fd5460..f8f32131b 100644
--- a/src/dotty/tools/dotc/transform/PatternMatcher.scala
+++ b/src/dotty/tools/dotc/transform/PatternMatcher.scala
@@ -307,10 +307,15 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer {thisTrans
       // TODO Deal with guards?
 
       def isSwitchableType(tpe: Type): Boolean = {
-        (tpe isRef defn.IntClass) ||
-        (tpe isRef defn.ByteClass) ||
-        (tpe isRef defn.ShortClass) ||
-        (tpe isRef defn.CharClass)
+        val actualTpe = tpe match {
+          case t @ AnnotatedType(inner, _) => inner
+          case x => x
+        }
+
+        (actualTpe isRef defn.IntClass) ||
+        (actualTpe isRef defn.ByteClass) ||
+        (actualTpe isRef defn.ShortClass) ||
+        (actualTpe isRef defn.CharClass)
       }
 
       object IntEqualityTestTreeMaker {
@@ -423,7 +428,8 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer {thisTrans
         Match(intScrut, newCases :+ defaultCase)
       }
 
-      if (isSwitchableType(scrut.tpe.widenDealias) && cases.forall(isSwitchCase)) {
+      val dealiased = scrut.tpe.widenDealias
+      if (isSwitchableType(dealiased) && cases.forall(isSwitchCase)) {
         val valuesToCases = cases.map(extractSwitchCase)
         val values = valuesToCases.map(_._1)
         if (values.tails.exists { tail => tail.nonEmpty && tail.tail.exists(doOverlap(_, tail.head)) }) {
@@ -433,6 +439,8 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer {thisTrans
           Some(makeSwitch(valuesToCases))
         }
       } else {
+        if (dealiased hasAnnotation defn.SwitchAnnot)
+          ctx.warning("failed to emit switch for `@switch` annotated match")
         None
       }
     }