add an isCompanionMethod convenience method

Author: smarter

src/dotty/tools/dotc/core/SymDenotations.scala

@@ -370,6 +370,15 @@ object SymDenotations {
     final def isAnonymousModuleVal(implicit ctx: Context) =
       this.symbol.is(ModuleVal) && (initial.asSymDenotation.name startsWith nme.ANON_CLASS)
 
+    /** Is this a companion class method or companion object method?
+     *  These methods are generated by Symbols#synthesizeCompanionMethod
+     *  and used in SymDenotations#companionClass and
+     *  SymDenotations#companionModule .
+     */
+    final def isCompanionMethod(implicit ctx: Context) =
+      name.toTermName == nme.COMPANION_CLASS_METHOD ||
+      name.toTermName == nme.COMPANION_MODULE_METHOD
+
     /** Is symbol a primitive value class? */
     def isPrimitiveValueClass(implicit ctx: Context) = defn.ScalaValueClasses contains symbol
 

src/dotty/tools/dotc/core/TypeErasure.scala

@@ -142,14 +142,14 @@ object TypeErasure {
    *   - For $asInstanceOf           : [T]T
    *   - For $isInstanceOf           : [T]Boolean
    *   - For all abstract types      : = ?
-   *   - For COMPANION_CLASS_METHOD  : the erasure of their type with semiEraseVCs = false,
-   *                                   this is needed to keep [[SymDenotation#companionClass]]
-   *                                   working after erasure for value classes.
+   *   - For companion methods       : the erasure of their type with semiEraseVCs = false.
+   *                                   The signature of these methods are used to keep a
+   *                                   link between companions and should not be semi-erased.
    *   - For all other symbols       : the semi-erasure of their types, with
    *                                   isJava, isConstructor set according to symbol.
    */
   def transformInfo(sym: Symbol, tp: Type)(implicit ctx: Context): Type = {
-    val semiEraseVCs = sym.name ne nme.COMPANION_CLASS_METHOD
+    val semiEraseVCs = !sym.isCompanionMethod
     val erase = erasureFn(sym is JavaDefined, semiEraseVCs, sym.isConstructor, wildcardOK = false)
 
     def eraseParamBounds(tp: PolyType): Type =

src/dotty/tools/dotc/transform/ValueClasses.scala

@@ -25,7 +25,7 @@ object ValueClasses {
       !d.isConstructor &&
       !d.is(SuperAccessor) &&
       !d.is(Macro) &&
-      !(d.name eq nme.COMPANION_MODULE_METHOD)
+      !d.isCompanionMethod
 
   /** The member that of a derived value class that unboxes it. */
   def valueClassUnbox(d: ClassDenotation)(implicit ctx: Context): Symbol =