Merge pull request #9226 from lrytz/t12002b

Keep `private[this] var` class parameter fields that are only read

src/compiler/scala/tools/nsc/transform/Constructors.scala

@@ -172,7 +172,7 @@ abstract class Constructors extends Statics with Transform with TypingTransforme
       //   class Outer { def test = {class LocalParent; class LocalChild extends LocalParent } }
       //
       // See run/t9408.scala for related test cases.
-      def omittableParamAcc(sym: Symbol) = sym.isParamAccessor && sym.isPrivateLocal
+      def omittableParamAcc(sym: Symbol) = sym.isParamAccessor && sym.isPrivateLocal && !sym.isVariable
       def omittableOuterAcc(sym: Symbol) = isEffectivelyFinal && sym.isOuterAccessor && !sym.isOverridingSymbol
       val omittables = mutable.Set.empty[Symbol] ++ (decls filter (sym => omittableParamAcc(sym) || omittableOuterAcc(sym))) // the closure only captures isEffectivelyFinal
 
@@ -192,28 +192,10 @@ abstract class Constructors extends Statics with Transform with TypingTransforme
             }
           }
       }
-      class DetectAssigns(targets: mutable.Set[Symbol]) extends InternalTraverser {
-        override def traverse(tree: Tree): Unit = if (targets.nonEmpty) {
-          tree match {
-            case Assign(lhs, _) if targets(lhs.symbol) =>
-              targets -= lhs.symbol
-              omittables -= lhs.symbol
-              tree.traverse(this)
-            case _ => tree.traverse(this)
-          }
-        }
-      }
 
       if (omittables.nonEmpty)
         (defs.iterator ++ auxConstructors.iterator) foreach detectUsages.traverse
 
-      if (omittables.nonEmpty) {
-        val omittedVars = omittables.filter(_.isVariable)
-        if (omittedVars.nonEmpty) {
-          val detector = new DetectAssigns(omittedVars)
-          constructor.foreach(detector.traverse)
-        }
-      }
       omittables.toSet
     }
   } // OmittablesHelper

test/files/run/t12002.check

@@ -1 +1,10 @@
 good boy!
+List()
+List()
+List(private int C.x)
+List(private int D.x)
+List(private int E.x)
+List(private int F.x)
+List(private int G.x)
+List(private final int H.x)
+List(private int I.x)

test/files/run/t12002.scala

@@ -1,17 +1,24 @@
-// cf t6880
-class C(private[this] var c: String) {
+class C0(private[this] var c: String) {
   private[this] var x: String = _
   c = "good"
   x = c + " boy!"
   override def toString = x
 }
 
+class A(x: Int) { assert(x == 1) } // elided
+class B(private[this] val x: Int) { assert(x == 1) } // elided
+class C(private[this] var x: Int) { } // kept
+class D(private[this] var x: Int) { assert(x == 1) } // kept
+class E(private[this] var x: Int) { x = 2 } // kept
+class F(private[this] var x: Int) { x = 2; assert(x == 2) } // kept
+class G(private[this] var x: Int) { x = 2; assert(x == 2); def m() = assert(x == 2, "m" + x); m() } // kept
+class H(private val x: Int) { } // kept
+class I(private var x: Int) { } // kept
+
 object Test {
-  def main(args: Array[String]) = println {
-    new C("bad")
+  def fs(o: AnyRef) = println(o.getClass.getDeclaredFields.toList)
+  def main(args: Array[String]): Unit = {
+    println(new C0("bad"))
+    List(new A(1), new B(1), new C(1), new D(1), new E(1), new F(1), new G(1), new H(1), new I(1)).foreach(fs)
   }
 }
-
-// was
-// java.lang.NoSuchFieldError: c
-//         at C.<init>(t12002.scala:6)