ParamForwarding: do not require param accessors to be private[this]

Also mark the forwarder as Stable otherwise we get a RefChecks error.

This fixes scala#608.

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

@@ -43,13 +43,13 @@ class ParamForwarding(thisTransformer: DenotTransformer) {
         stat match {
           case stat: ValDef =>
             val sym = stat.symbol.asTerm
-            if (sym is (PrivateLocalParamAccessor, butNot = Mutable)) {
+            if (sym is (ParamAccessor, butNot = Mutable)) {
               val idx = superArgs.indexWhere(_.symbol == sym)
               if (idx >= 0 && superParamNames(idx) == stat.name) { // supercall to like-named parameter
                 val alias = inheritedAccessor(sym)
                 if (alias.exists) {
                   def forwarder(implicit ctx: Context) = {
-                    sym.copySymDenotation(initFlags = sym.flags | Method, info = sym.info.ensureMethodic)
+                    sym.copySymDenotation(initFlags = sym.flags | Method | Stable, info = sym.info.ensureMethodic)
                       .installAfter(thisTransformer)
                     val superAcc =
                       Super(This(currentClass), tpnme.EMPTY, inConstrCall = false).select(alias)

tests/run/paramForwarding.check

@@ -0,0 +1,16 @@
+B:
+private final int B.theValue$$local
+private final int B.theValueInB$$local
+Bz:
+private final int Bz.theValue$$local
+private final int Bz.theValueInBz$$local
+C:
+
+D:
+private final int D.other$$local
+NonVal:
+
+X:
+private final int X.theValue$$local
+Y:
+private final int Y.theValue$$local

tests/run/paramForwarding.scala

@@ -0,0 +1,89 @@
+// A contains a field A.theValue$$local accessible using the
+// generated getter A.theValue()
+class A(val theValue: Int) {
+  val theValueInA = theValue // use the constructor parameter theValue
+
+  def getTheValue = theValue // virtual call to the getter theValue()
+}
+
+// B contains a field B.theValue$$local accessible using the getter
+// B.theValue() which overrides A.theValue()
+class B(override val theValue: Int) extends A(42) {
+  val theValueInB = theValue
+}
+
+// Bz contains a field Bz.theValue$$local accessible using the getter
+// Bz.theValue() which overrides A.theValue()
+class Bz extends A(42) {
+  override val theValue: Int = 10
+  val theValueInBz = theValue
+}
+
+// C does not contains a field C.theValue$$local, it contains
+// a getter C.theValue() which only calls super.theValue()
+class C(override val theValue: Int) extends A(theValue)
+
+// D contains a field D.other$$local and a corresponding getter.
+class D(val other: Int) extends A(other)
+
+
+// NonVal does not contain a field NonVal.theValue$$local.
+class NonVal(theValue: Int) extends A(theValue) {
+  def getTheValueInNonVal = theValue // use the constructor parameter theValue
+}
+
+// X contains a field X.theValue$$local accessible using the getter
+// X.theValue() which overrides A.theValue()
+class X(override val theValue: Int) extends NonVal(0)
+
+// Y contains a field Y.theValue$$local accessible using the getter
+// Y.theValue() which overrides A.theValue()
+class Y(override val theValue: Int) extends NonVal(theValue)
+
+
+object Test {
+  def printFields(obj: Any) =
+    println(obj.getClass.getDeclaredFields.map(_.toString).sorted.deep.mkString("\n"))
+
+  def main(args: Array[String]): Unit = {
+    val b10 = new B(10)
+    val bz = new Bz
+    val c11 = new C(11)
+    val d12 = new D(12)
+    val nv13 = new NonVal(13)
+    val x14 = new X(14)
+    val y15 = new Y(15)
+
+    println("B:")
+    printFields(b10)
+    println("Bz:")
+    printFields(bz)
+    println("C:")
+    printFields(c11)
+    println("D:")
+    printFields(d12)
+    println("NonVal:")
+    printFields(nv13)
+    println("X:")
+    printFields(x14)
+    println("Y:")
+    printFields(y15)
+
+
+    assert(b10.getTheValue == 10)
+    assert(b10.theValue == 10)
+    assert(b10.theValueInB == 10)
+    assert(b10.theValueInA == 42)
+
+    assert(bz.getTheValue == 10)
+    assert(bz.theValue == 10)
+    assert(bz.theValueInBz == 10)
+    assert(bz.theValueInA == 42)
+
+
+    assert(x14.theValue == 14)
+    assert(x14.getTheValue == 14)
+    assert(x14.getTheValueInNonVal == 0)
+    assert(x14.theValueInA == 0)
+  }
+}