Fix #3588: Do not emit switch when matching on Any

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

@@ -812,7 +812,8 @@ object PatternMatcher {
           plan :: Nil
       }
 
-      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(
@@ -181,6 +182,7 @@ class CompilationTests extends ParallelTesting {
     compileFile("../tests/neg-custom-args/overloadsOnAbstractTypes.scala", allowDoubleBindings) +
     compileFile("../tests/neg-custom-args/xfatalWarnings.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("../tests/neg-custom-args/pureStatement.scala", defaultOptions.and("-Xfatal-warnings")) +
+    compileFile("../tests/neg-custom-args/i3589-a.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("../tests/neg-custom-args/phantom-overload.scala", allowDoubleBindings) +
     compileFile("../tests/neg-custom-args/phantom-overload-2.scala", allowDoubleBindings) +
     compileFile("../tests/neg-custom-args/structural.scala", defaultOptions.and("-Xfatal-warnings"))

tests/neg-custom-args/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
+  }
+}

tests/pos/i3588.scala

@@ -0,0 +1,51 @@
+class Foo {
+  val a: Any = 3
+  a match {
+    case 1 =>
+    case 2 =>
+    case 3 =>
+    case _ =>
+  }
+}
+
+class Bar[T] {
+  val a: T = ???
+  a match {
+    case 1 =>
+    case 2 =>
+    case 3 =>
+    case _ =>
+  }
+}
+
+class Baz {
+  val a: Double = 1.0
+  a match {
+    case 1 =>
+    case 2 =>
+    case 3 =>
+    case _ =>
+  }
+}
+
+class Foo2 {
+  val a: AnyVal = 3
+  a match {
+    case 1 =>
+    case 2 =>
+    case 3 =>
+    case _ =>
+  }
+}
+
+
+case class A(i: Int) extends AnyVal
+class Foo3 {
+  val a: A = new A(3)
+  a match {
+    case A(1) =>
+    case A(2) =>
+    case A(3) =>
+    case _ =>
+  }
+}