Add tests and only try switches for Char, Int, Short and Byte

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -791,6 +791,12 @@ object PatternMatcher {
      *  plan and following onSuccess plans.
      */
     private def collectSwitchCases(plan: TestPlan): List[Plan] = {
+      def isSwitchableType(tpe: Type): Boolean =
+        (tpe isRef defn.IntClass) ||
+        (tpe isRef defn.ByteClass) ||
+        (tpe isRef defn.ShortClass) ||
+        (tpe isRef defn.CharClass)
+
       val scrutinee = plan.scrutinee
 
       def isIntConst(tree: Tree) = tree match {
@@ -805,9 +811,9 @@ object PatternMatcher {
         case _ =>
           plan :: Nil
       }
-      val cls = scrutinee.tpe.widen.classSymbol
-      if (cls == defn.AnyClass || cls == defn.AnyValClass) Nil
-      else recur(plan)
+
+      if (isSwitchableType(scrutinee.tpe.widen)) recur(plan)
+      else Nil
     }
 
     /** Emit cases of a switch */

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -55,6 +55,7 @@ class CompilationTests extends ParallelTesting {
     compileFile("../tests/pos-scala2/rewrites.scala", scala2Mode.and("-rewrite")).copyToTarget() +
     compileFile("../tests/pos-special/utf8encoded.scala", explicitUTF8) +
     compileFile("../tests/pos-special/utf16encoded.scala", explicitUTF16) +
+    compileFile("../tests/pos-special/i3589-b.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileList(
       "compileMixed",
       List(
@@ -179,6 +180,7 @@ class CompilationTests extends ParallelTesting {
     compileFile("../tests/neg/customArgs/overloadsOnAbstractTypes.scala", allowDoubleBindings) +
     compileFile("../tests/neg/customArgs/xfatalWarnings.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("../tests/neg/customArgs/pureStatement.scala", defaultOptions.and("-Xfatal-warnings")) +
+    compileFile("../tests/neg/customArgs/i3589-a.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("../tests/neg/customArgs/phantom-overload.scala", allowDoubleBindings) +
     compileFile("../tests/neg/customArgs/phantom-overload-2.scala", allowDoubleBindings) +
     compileFile("../tests/neg/tailcall/t1672b.scala", defaultOptions) +

tests/neg/customArgs/i3589-a.scala

@@ -0,0 +1,10 @@
+object Test {
+  case class IntAnyVal(x: Int) extends AnyVal
+
+  def test(x: IntAnyVal) = (x: @annotation.switch) match { //error: warning: could not emit switch
+    case IntAnyVal(1) => 1
+    case IntAnyVal(2) => 2
+    case IntAnyVal(3) => 3
+    case _ => 4
+  }
+}

tests/pos-special/i3589-b.scala

@@ -0,0 +1,7 @@
+class Test {
+  def test(x: 1) = (x: @annotation.switch) match {
+    case 1 => 1
+    case 2 => 2
+    case 3 => 3
+  }
+}