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

Author: nicolasstucki

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

@@ -834,7 +834,9 @@ object PatternMatcher {
       }
       plan match {
         case plan: TestPlan =>
-          val switchCases = collectSwitchCases(plan)
+          val switchCases =
+            if (plan.scrutinee.tpe.widen.classSymbol == defn.AnyClass) Nil
+            else collectSwitchCases(plan)
           if (switchCases.lengthCompare(4) >= 0) // at least 3 cases + default
             Match(plan.scrutinee, emitSwitchCases(switchCases))
           else

tests/pos/i3588.scala

@@ -0,0 +1,19 @@
+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 _ =>
+  }
+}