Add code to disable old implicit closure syntax in blocks

This will no longer be supported. On the other hand, as long as
the alternative is not yet legal in Scala2.x we cannot flag this
as an error. So the migration warning/error and patch code is
currently disabled.

Author: odersky

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

@@ -1128,8 +1128,18 @@ object Parsers {
         val name = bindingName()
         val t =
           if (in.token == COLON && location == Location.InBlock) {
+            if (false) // Don't error yet, as the alternative syntax "implicit (x: T) => ... "
+                       // is not supported by Scala2.x
+              migrationWarningOrError(s"This syntax is no longer supported; parameter needs to be enclosed in (...)")
+
             in.nextToken()
-            infixType()
+            val t = infixType()
+
+            if (false && in.isScala2Mode) {
+              patch(source, Position(start), "(")
+              patch(source, Position(in.lastOffset), ")")
+            }
+            t
           }
           else TypeTree()
         (atPos(start) { makeParameter(name, t, mods) }) :: Nil