[SPARK-5040][SQL] Support expressing unresolved attributes using $"attribute name" notation in SQL DSL.

Author: Reynold Xin <rxin@databricks.com>

Closes #3862 from rxin/stringcontext-attr and squashes the following commits:

9b10f57 [Reynold Xin] Rename StrongToAttributeConversionHelper
72121af [Reynold Xin] [SPARK-5040][SQL] Support expressing unresolved attributes using $"attribute name" notation in SQL DSL.

1 files changed, 9 insertions, 0 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/dsl/package.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/dsl/package.scala
index 8e39f79d2c..9608e15c0f 100755
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/dsl/package.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/dsl/package.scala
@@ -135,6 +135,15 @@ package object dsl {
     implicit def symbolToUnresolvedAttribute(s: Symbol): analysis.UnresolvedAttribute =
       analysis.UnresolvedAttribute(s.name)
 
+    /** Converts $"col name" into an [[analysis.UnresolvedAttribute]]. */
+    implicit class StringToAttributeConversionHelper(val sc: StringContext) {
+      // Note that if we make ExpressionConversions an object rather than a trait, we can
+      // then make this a value class to avoid the small penalty of runtime instantiation.
+      def $(args: Any*): analysis.UnresolvedAttribute = {
+        analysis.UnresolvedAttribute(sc.s(args :_*))
+      }
+    }
+
     def sum(e: Expression) = Sum(e)
     def sumDistinct(e: Expression) = SumDistinct(e)
     def count(e: Expression) = Count(e)