better fix for see #3667.

4 files changed, 15 insertions, 6 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/NamesDefaults.scala b/src/compiler/scala/tools/nsc/typechecker/NamesDefaults.scala
index d846412185..35bb661377 100644
--- a/src/compiler/scala/tools/nsc/typechecker/NamesDefaults.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/NamesDefaults.scala
@@ -512,7 +512,15 @@ trait NamesDefaults { self: Analyzer =>
   def companionModuleOf(clazz: Symbol, context: Context) = {
     var res = clazz.companionModule
     if (res == NoSymbol)
-      res = context.lookup(clazz.name.toTermName, clazz.owner)
+      res = context.lookup(clazz.name.toTermName, clazz.owner).suchThat(sym =>
+        sym.hasFlag(MODULE) && sym.isCoDefinedWith(clazz))
+    res
+  }
+
+  def companionClassOf(module: Symbol, context: Context) = {
+    var res = module.companionClass
+    if (res == NoSymbol)
+      res = context.lookup(module.name.toTypeName, module.owner).suchThat(_.isCoDefinedWith(module))
     res
   }
 
diff --git a/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala b/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala
index 44930ffc81..0da00f5b83 100644
--- a/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala
@@ -290,15 +290,18 @@ trait SyntheticMethods extends ast.TreeDSL {
       }
 
       if (clazz.isModuleClass) {
-        if (!hasSerializableAnnotation(clazz))
-          clazz addAnnotation AnnotationInfo(SerializableAttr.tpe, Nil, Nil)
+        if (!hasSerializableAnnotation(clazz)) {
+          val comp = companionClassOf(clazz, context)
+          if (comp.hasFlag(Flags.CASE) || hasSerializableAnnotation(comp))
+            clazz addAnnotation AnnotationInfo(SerializableAttr.tpe, Nil, Nil)
+        }
 
         /** If you serialize a singleton and then deserialize it twice,
          *  you will have two instances of your singleton, unless you implement
          *  the readResolve() method (see http://www.javaworld.com/javaworld/
          *  jw-04-2003/jw-0425-designpatterns_p.html)
          */
-        if (!hasImplementation(nme.readResolve))
+        if (hasSerializableAnnotation(clazz) && !hasImplementation(nme.readResolve))
           ts += readResolveMethod
       }
     } catch {
diff --git a/test/files/scalap/packageObject/result.test b/test/files/scalap/packageObject/result.test
index 324992aae1..6a8d6ae1d5 100644
--- a/test/files/scalap/packageObject/result.test
+++ b/test/files/scalap/packageObject/result.test
@@ -2,5 +2,4 @@ package object PackageObject extends java.lang.Object with scala.ScalaObject {
   def this() = { /* compiled code */ }
   type A = scala.Predef.String
   def foo(i : scala.Int) : scala.Int = { /* compiled code */ }
-  protected def readResolve() : java.lang.Object = { /* compiled code */ }
 }
diff --git a/test/files/scalap/traitObject/result.test b/test/files/scalap/traitObject/result.test
index 8978873fc7..0d7de1535d 100644
--- a/test/files/scalap/traitObject/result.test
+++ b/test/files/scalap/traitObject/result.test
@@ -5,5 +5,4 @@ trait TraitObject extends java.lang.Object with scala.ScalaObject {
 object TraitObject extends java.lang.Object with scala.ScalaObject {
   def this() = { /* compiled code */ }
   def bar : scala.Int = { /* compiled code */ }
-  protected def readResolve() : java.lang.Object = { /* compiled code */ }
 }