compareTo implemented for enums

Author: anatoliykmetyuk

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

@@ -82,9 +82,6 @@ class SyntheticMethods(thisPhase: DenotTransformer) {
 
     def removeColors(msg: String): String = msg.replaceAll("\u001b\\[.*?m", "")
     def syntheticDef(sym: Symbol): Tree = {
-      // if (removeColors(sym.show) == "method getDeclaringClass")
-      //   println(s"Sym ${sym.show} info ${sym.denot.info.show} asf ${clazz.info.parents.head.show}: " +
-      //     s"${sym.denot.asSeenFrom(clazz.info.parents.head).info.show}")
       val synthetic = sym
         .copy(
           owner = clazz,
@@ -112,13 +109,35 @@ class SyntheticMethods(thisPhase: DenotTransformer) {
         // Enum Methods
         case nme.name => _ => Literal(Constant("Hello World"))
         case nme.ordinal => _ => Literal(Constant(0))
-        case nme.compareTo => _ => Literal(Constant(0))
+        case nme.compareTo => vrefss => compareToBody(vrefss.head.head)
         case nme.getDeclaringClass => _ => Literal(Constant(null))
       }
       ctx.log(s"adding $synthetic to $clazz at ${ctx.phase}")
       DefDef(synthetic, syntheticRHS(ctx.withOwner(synthetic))).withSpan(ctx.owner.span.focus)
     }
 
+    /** An enum case `X` in
+     *
+     * ```
+     * enum Foo { case X }
+     * ```
+     *
+     * gets the `compareTo` method:
+     *
+     * ```
+     * def compareTo(other: Foo): Int =
+     *   new Integer(this).ordinal.compareTo(new Integer(other.ordinal))
+     * ```
+     */
+    def compareToBody(other: Tree): Tree = {
+      val thisOrdinal = This(clazz).select(defn.Enum_ordinal)
+      val thisOrdinalBoxed = New(defn.BoxedIntType, thisOrdinal :: Nil)
+      val otherOrdinal = other.select(defn.Enum_ordinal)
+      val otherOrdinalBoxed = New(defn.BoxedIntType, otherOrdinal :: Nil)
+      val thisOrdinalCompareTo = thisOrdinalBoxed.select(defn.Comparable_compareTo)
+      Apply(thisOrdinalCompareTo, otherOrdinalBoxed :: Nil)
+    }
+
     /** The class
      *
      *  ```