Fix #3588: Do not emit switch when matching on non switchable types

Author: nicolasstucki

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

@@ -811,8 +811,8 @@ object PatternMatcher {
         case _ =>
           plan :: Nil
       }
-
-      recur(plan)
+      if (isSwitchableType(scrutinee.tpe)) recur(plan)
+      else Nil
     }
 
     /** Emit cases of a switch */

tests/pos/i3588.scala

@@ -0,0 +1,29 @@
+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 _ =>
+  }
+}