Fix #1976: Hack to support scala.xml's $scope (#1977)

This is a gross hack to support the need for a $scope
binding when XML literals are created. It should go away
once we phase out XML literals.  A library-based
solution should use implicits instead.

Author: odersky

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -527,6 +527,8 @@ class Definitions {
   lazy val EqType = ctx.requiredClassRef("scala.Eq")
   def EqClass(implicit ctx: Context) = EqType.symbol.asClass
 
+  lazy val XMLTopScopeModuleRef = ctx.requiredModuleRef("scala.xml.TopScope")
+
   // Annotation base classes
   lazy val AnnotationType              = ctx.requiredClassRef("scala.annotation.Annotation")
   def AnnotationClass(implicit ctx: Context) = AnnotationType.symbol.asClass

compiler/src/dotty/tools/dotc/core/StdNames.scala

@@ -533,6 +533,7 @@ object StdNames {
     val nullRuntimeClass: N     = "scala.runtime.Null$"
 
     val synthSwitch: N          = "$synthSwitch"
+    val _scope: N               = "$scope"
 
     // unencoded operators
     object raw {

compiler/src/dotty/tools/dotc/parsing/SymbolicXMLBuilder.scala

@@ -55,7 +55,6 @@ class SymbolicXMLBuilder(parser: Parser, preserveWS: Boolean)(implicit ctx: Cont
     val _buf: TermName      = "$buf"
     val _md: TermName       = "$md"
     val _plus: TermName     = "$amp$plus"
-    val _scope: TermName    = "$scope"
     val _tmpscope: TermName = "$tmpscope"
     val _xml: TermName      = "xml"
   }

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -351,6 +351,11 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
     val ownType =
       if (rawType.exists)
         ensureAccessible(rawType, superAccess = false, tree.pos)
+      else if (name == nme._scope) {
+        // gross hack to support current xml literals.
+        // awaiting a better implicits based solution for library-supported xml
+        return ref(defn.XMLTopScopeModuleRef)
+      }
       else
         errorType(new MissingIdent(tree, kind, name.show), tree.pos)
 

tests/pos/i1976.scala

@@ -0,0 +1,4 @@
+object Test {
+  import scala.xml._
+  val node = <node>{ "whatever " }</node>
+}