Fix equals method for value classes

Before this commit, the following class:
  class VC(val x: Int) extends AnyVal
resulted in the creation of the method:
  def equals(val x$0: Any): Boolean =
    x$0 match {
      case x$0 @ _: VC => true
      case _: Any => false
    }
After this commit, we get instead:
  def equals(val x$0: Any): Boolean =
    x$0 match {
      case x$0 @ _: VC => VC.this.a.==(x$0.a)
      case _: Any => false
    }

Author: smarter

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

@@ -79,6 +79,9 @@ class SymUtils(val self: Symbol) extends AnyVal {
   def accessorNamed(name: TermName)(implicit ctx: Context): Symbol =
     self.owner.info.decl(name).suchThat(_ is Accessor).symbol
 
+  def termParamAccessors(implicit ctx: Context): List[Symbol] =
+    self.info.decls.filter(_ is TermParamAccessor).toList
+
   def caseAccessors(implicit ctx:Context) =
     self.info.decls.filter(_ is CaseAccessor).toList
 

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

@@ -49,7 +49,11 @@ class SyntheticMethods extends MiniPhaseTransform with IdentityDenotTransformer
    */
   def syntheticMethods(clazz: ClassSymbol)(implicit ctx: Context): List[Tree] = {
     val clazzType = clazz.typeRef
-    lazy val accessors = clazz.caseAccessors
+    lazy val accessors =
+      if (isDerivedValueClass(clazz))
+        clazz.termParamAccessors
+      else
+        clazz.caseAccessors
 
     val symbolsToSynthesize: List[Symbol] =
       if (clazz.is(Case)) caseSymbols