Set scene for Predef.$scope's demise.

When there's no Predef.$scope but xml is being used,
the compiler aliases scala.xml.TopScope to $scope.

There must be a scala.xml package when xml literals were parsed.

For compatibility with the old library, which relied on $scope being in scope,
synthesize a `import scala.xml.{TopScope => $scope}` when xml is needed,
but there's no Predef.$scope and the old library is detected (scala.xml.TopScope exists).

1 files changed, 7 insertions, 1 deletions

diff --git a/src/library/scala/Predef.scala b/src/library/scala/Predef.scala
index 5ba38600b6..a188602543 100644
--- a/src/library/scala/Predef.scala
+++ b/src/library/scala/Predef.scala
@@ -134,7 +134,13 @@ object Predef extends LowPriorityImplicits with DeprecatedPredef {
   @inline def implicitly[T](implicit e: T) = e    // for summoning implicit values from the nether world -- TODO: when dependent method types are on by default, give this result type `e.type`, so that inliner has better chance of knowing which method to inline in calls like `implicitly[MatchingStrategy[Option]].zero`
   @inline def locally[T](x: T): T  = x    // to communicate intent and avoid unmoored statements
 
-  // Apparently needed for the xml library
+  // TODO: remove `val $scope = ...` as soon as 2.11.0-M4 is released and used as STARR
+  // As it has a '$' in its name, we don't have to deprecate first.
+  // The compiler now aliases `scala.xml.TopScope` to `$scope` (unless Predef.$scope is still there).
+  // This definition left in place for older compilers and to compile quick with pre-2.11.0-M4 STARR.
+  // In principle we don't need it to compile library/reflect/compiler (there's no xml left there),
+  // so a new locker can be built without this definition, and locker can build quick
+  // (partest, scaladoc still require xml).
   val $scope = scala.xml.TopScope
 
   // errors and asserts -------------------------------------------------