Fixed #2497

9 files changed, 27 insertions, 24 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
index d273af60c5..31ebdc5906 100644
--- a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
@@ -234,7 +234,7 @@ abstract class RefChecks extends InfoTransform {
       }
 
       /** Check that all conditions for overriding <code>other</code> by
-       *  <code>member</code> are met.
+       *  <code>member</code> of class <code>clazz</code> are met.
        */
       def checkOverride(clazz: Symbol, member: Symbol, other: Symbol) {
 
@@ -271,9 +271,9 @@ abstract class RefChecks extends InfoTransform {
         // return if we already checked this combination elsewhere
         if (member.owner != clazz) {
           if ((member.owner isSubClass other.owner) && (member.isDeferred || !other.isDeferred)) {
-                //Console.println(infoString(member) + " shadows1 " + infoString(other) " in " + clazz);//DEBUG
-                return;
-              }
+            //Console.println(infoString(member) + " shadows1 " + infoString(other) " in " + clazz);//DEBUG
+            return;
+          }
           if (clazz.info.parents exists (parent =>
             (parent.typeSymbol isSubClass other.owner) && (parent.typeSymbol isSubClass member.owner) &&
             (member.isDeferred || !other.isDeferred))) {
@@ -287,6 +287,11 @@ abstract class RefChecks extends InfoTransform {
             }
         }
 
+        /** Is the intersection between given two lists of overridden symbols empty?
+         */
+        def intersectionIsEmpty(syms1: List[Symbol], syms2: List[Symbol]) =
+          !(syms1 exists (syms2 contains))
+
         if (member hasFlag PRIVATE) { // (1.1)
           overrideError("has weaker access privileges; it should not be private")
         }
@@ -310,6 +315,12 @@ abstract class RefChecks extends InfoTransform {
         } else if ((member hasFlag (OVERRIDE | ABSOVERRIDE)) &&
                    (other hasFlag ACCESSOR) && other.accessed.isVariable && !other.accessed.hasFlag(LAZY)) {
           overrideError("cannot override a mutable variable")
+        } else if ((member hasFlag (OVERRIDE | ABSOVERRIDE)) &&
+                   !(member.owner isSubClass other.owner) &&
+                   !member.isDeferred && !other.isDeferred &&
+                   intersectionIsEmpty(member.allOverriddenSymbols, other.allOverriddenSymbols)) {
+          overrideError("cannot override a concrete member without a third member that's overridden by both "+
+                        "(this rule is designed to prevent ``accidental overrides'')")
         } else if (other.isStable && !member.isStable) { // (1.4)
           overrideError("needs to be a stable, immutable value")
         } else if (member.isValue && (member hasFlag LAZY) &&
diff --git a/src/library/scala/collection/TraversableLike.scala b/src/library/scala/collection/TraversableLike.scala
index 57f9840804..4fdaa6fee2 100644
--- a/src/library/scala/collection/TraversableLike.scala
+++ b/src/library/scala/collection/TraversableLike.scala
@@ -63,7 +63,7 @@ import annotation.experimental
  *  @version 2.8
  *  @since   2.8
  */
-trait TraversableLike[+A, +Repr] {
+trait TraversableLike[+A, +Repr] extends HasNewBuilder[A, Repr] {
 self =>
 
   import Traversable.breaks._
diff --git a/src/library/scala/collection/generic/GenericTraversableTemplate.scala b/src/library/scala/collection/generic/GenericTraversableTemplate.scala
index 50a7aa3fe0..cf4f3abdd2 100644
--- a/src/library/scala/collection/generic/GenericTraversableTemplate.scala
+++ b/src/library/scala/collection/generic/GenericTraversableTemplate.scala
@@ -18,7 +18,7 @@ import annotation.unchecked.uncheckedVariance
 /**
  * @since 2.8
  */
-trait GenericTraversableTemplate[+A, +CC[X] <: Traversable[X]] {
+trait GenericTraversableTemplate[+A, +CC[X] <: Traversable[X]] extends HasNewBuilder[A, CC[A] @uncheckedVariance] {
 
   def foreach[U](f: A => U): Unit
   def head: A
diff --git a/src/library/scala/collection/mutable/FlatHashTable.scala b/src/library/scala/collection/mutable/FlatHashTable.scala
index 1861953eec..1d55933050 100644
--- a/src/library/scala/collection/mutable/FlatHashTable.scala
+++ b/src/library/scala/collection/mutable/FlatHashTable.scala
@@ -40,10 +40,6 @@ trait FlatHashTable[A] {
    */
   protected var threshold: Int = newThreshold(initialSize)
 
-  /** Returns the number of entires in this hash table.
-   */
-  def size: Int = tableSize
-
   def findEntry(elem: A): Option[A] = {
     var h = index(elemHashCode(elem))
     var entry = table(h)
@@ -163,7 +159,7 @@ trait FlatHashTable[A] {
     (size.toLong * lf / loadFactorDenum ).toInt
   }
 
-  protected def clear() {
+  protected def clearTable() {
     var i = table.length - 1
     while (i >= 0) { table(i) = null; i -= 1 }
     tableSize = 0
diff --git a/src/library/scala/collection/mutable/HashMap.scala b/src/library/scala/collection/mutable/HashMap.scala
index 2591557c78..b2f259e4e9 100644
--- a/src/library/scala/collection/mutable/HashMap.scala
+++ b/src/library/scala/collection/mutable/HashMap.scala
@@ -23,8 +23,8 @@ class HashMap[A, B] extends Map[A, B]
                        with HashTable[A] {
 
   override def empty: HashMap[A, B] = HashMap.empty[A, B]
-  override def clear() = super.clear()
-  override def size: Int = super[HashTable].size
+  override def clear() = clearTable()
+  override def size: Int = tableSize
 
   type Entry = DefaultEntry[A, B]
 
diff --git a/src/library/scala/collection/mutable/HashSet.scala b/src/library/scala/collection/mutable/HashSet.scala
index 9f24a0b341..9144a4be88 100644
--- a/src/library/scala/collection/mutable/HashSet.scala
+++ b/src/library/scala/collection/mutable/HashSet.scala
@@ -28,7 +28,7 @@ class HashSet[A] extends Set[A]
                     with FlatHashTable[A] {
   override def companion: GenericCompanion[HashSet] = HashSet
 
-  override def size = super.size
+  override def size = tableSize
 
   def contains(elem: A): Boolean = containsEntry(elem)
 
@@ -38,7 +38,7 @@ class HashSet[A] extends Set[A]
   override def add(elem: A): Boolean = addEntry(elem)
   override def remove(elem: A): Boolean = removeEntry(elem).isDefined
 
-  override def clear() = super.clear()
+  override def clear() = clearTable()
 
   override def foreach[U](f: A =>  U) {
     var i = 0
diff --git a/src/library/scala/collection/mutable/HashTable.scala b/src/library/scala/collection/mutable/HashTable.scala
index 9d3a35376c..9dd8a7aeb0 100644
--- a/src/library/scala/collection/mutable/HashTable.scala
+++ b/src/library/scala/collection/mutable/HashTable.scala
@@ -75,10 +75,6 @@ trait HashTable[A] {
    */
   protected var threshold: Int = initialThreshold
 
-  /** Returns the size of this hash table.
-   */
-  def size = tableSize
-
   /** Find entry with given key in table, null if not found
    */
   protected def findEntry(key: A): Entry = {
@@ -154,7 +150,7 @@ trait HashTable[A] {
 
   /** Remove all entries from table
    */
-  def clear() {
+  protected def clearTable() {
     var i = table.length - 1
     while (i >= 0) { table(i) = null; i = i - 1 }
     tableSize = 0
diff --git a/src/library/scala/collection/mutable/LinkedHashMap.scala b/src/library/scala/collection/mutable/LinkedHashMap.scala
index 5c17ef1cfb..b0cad79ef4 100644
--- a/src/library/scala/collection/mutable/LinkedHashMap.scala
+++ b/src/library/scala/collection/mutable/LinkedHashMap.scala
@@ -35,7 +35,7 @@ class LinkedHashMap[A, B] extends Map[A, B]
                              with HashTable[A] {
 
   override def empty = LinkedHashMap.empty[A, B]
-  override def size = super[HashTable].size
+  override def size = tableSize
 
   type Entry = LinkedEntry[A, B]
 
@@ -112,7 +112,7 @@ class LinkedHashMap[A, B] extends Map[A, B]
   }
 
   override def clear() {
-    super[HashTable].clear()
+    clearTable()
     firstEntry = null
   }
 }
diff --git a/src/library/scala/collection/mutable/LinkedHashSet.scala b/src/library/scala/collection/mutable/LinkedHashSet.scala
index fd606badec..081b068723 100644
--- a/src/library/scala/collection/mutable/LinkedHashSet.scala
+++ b/src/library/scala/collection/mutable/LinkedHashSet.scala
@@ -27,7 +27,7 @@ class LinkedHashSet[A] extends Set[A]
 
   protected val ordered = new ListBuffer[A]
 
-  override def size = super.size
+  override def size = tableSize
 
   def contains(elem: A): Boolean = containsEntry(elem)
 
@@ -46,7 +46,7 @@ class LinkedHashSet[A] extends Set[A]
 
   override def clear() {
     ordered.clear()
-    super.clear()
+    clearTable()
   }
 
   override def iterator = ordered.iterator