Overhaul of JavaConver{sions,ters}.

Initially motivated by SI-5580, then just motivated.  I broke up
the opaquely named JavaConversions and JavaConverters into the following
traits encapsulating some permutation of

  { to java, to scala, bidirectional }
  { wrappers, decorators }

I named everything consistently in terms of either Wrappers
or Decorators.  Decorators install those asJava/asScala methods
onto collections of the right kind; Wrappers hide the process.

JavaConversions then reduces to an object which (ill-advisedly)
extends both WrapAsJava and WrapAsScala.  And JavaConverters is
an object extending DecorateAsScala and DecorateAsJava.  However
other more clearly named vals exist in the newly created
scala.collection.convert package object.

  val decorateAsJava  = new DecorateAsJava { }
  val decorateAsScala = new DecorateAsScala { }
  val decorateAll     = new DecorateAsJava with DecorateAsScala { }
  val wrapAsJava      = new WrapAsJava { }
  val wrapAsScala     = new WrapAsScala { }
  val wrapAll         = new WrapAsJava with WrapAsScala { }

So for instance to import asScala decorators, and only those:

  scala> import scala.collection.convert.decorateAsScala._
  import scala.collection.convert.decorateAsScala._

  scala> new java.util.ArrayList[String].asScala groupBy (x => x)
  res0: scala.collection.immutable.Map[String,scala.collection.mutable.Buffer[String]] = Map()

I propose we put those vals or a subset of them in the scala
package object rather than way down in scala.collection.convert.

1 files changed, 19 insertions, 0 deletions

diff --git a/test/files/pos/t5580b.scala b/test/files/pos/t5580b.scala
new file mode 100644
index 0000000000..d5a4a0a2b2
--- /dev/null
+++ b/test/files/pos/t5580b.scala
@@ -0,0 +1,19 @@
+/** It's a pos test because it does indeed compile,
+ *  not so much because I'm glad it does.  Testing
+ *  that error messages created and discarded during
+ *  implicit search don't blow it up.
+ */
+
+import scala.collection.mutable.WeakHashMap
+import scala.collection.JavaConversions._
+
+class bar { }
+
+class foo {
+  val map = WeakHashMap[AnyRef, collection.mutable.Map[bar, collection.mutable.Set[bar]]]()
+
+  def test={
+    val tmp:bar=null
+    if (map.get(tmp).isEmpty) map.put(tmp,collection.mutable.Set())
+  }
+}