Make currentClass available from Symbols

It's needed beyond MacroTransform, and its definition
is independent.

Also, make `defn` in Symbols not implicit. (I think its
implicitness was an oversight).

Author: odersky

src/dotty/tools/dotc/core/Symbols.scala

@@ -552,13 +552,17 @@ object Symbols {
         ctx.newSymbol(owner, name, flags, info, privateWithin, coord)
   }
 
-  implicit def defn(implicit ctx: Context): Definitions = ctx.definitions
-
   /** Makes all denotation operations available on symbols */
   implicit def toDenot(sym: Symbol)(implicit ctx: Context): SymDenotation = sym.denot
 
   /** Makes all class denotations available on class symbols */
   implicit def toClassDenot(cls: ClassSymbol)(implicit ctx: Context): ClassDenotation = cls.classDenot
 
+  /** The Definitions object */
+  def defn(implicit ctx: Context): Definitions = ctx.definitions
+  
+  /** The current class */
+  def currentClass(implicit ctx: Context): ClassSymbol = ctx.owner.enclosingClass.asClass
+
   var stubs: List[Symbol] = Nil // diagnostic
 }

src/dotty/tools/dotc/transform/MacroTransform.scala

@@ -38,11 +38,6 @@ abstract class MacroTransform extends Phase {
       ctx.fresh.setTree(tree).setOwner(owner)
     }
 
-    /** The current enclosing class
-     *  @pre  We must be inside a class
-     */
-    def currentClass(implicit ctx: Context): ClassSymbol = ctx.owner.enclosingClass.asClass
-
     def transformStats(trees: List[Tree], exprOwner: Symbol)(implicit ctx: Context): List[Tree] = {
       def transformStat(stat: Tree): Tree = stat match {
         case _: Import | _: DefTree => transform(stat)