[SPARK-7834] [SQL] Better window error messages

Author: Michael Armbrust <michael@databricks.com>

Closes #6363 from marmbrus/windowErrors and squashes the following commits:

516b02d [Michael Armbrust] [SPARK-7834] [SQL] Better window error messages

(cherry picked from commit 3c1305107a)
Signed-off-by: Michael Armbrust <michael@databricks.com>

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CheckAnalysis.scala

@@ -71,6 +71,11 @@ trait CheckAnalysis {
               s"invalid expression ${b.prettyString} " +
               s"between ${b.left.dataType.simpleString} and ${b.right.dataType.simpleString}")
 
+          case WindowExpression(UnresolvedWindowFunction(name, _), _) =>
+            failAnalysis(
+              s"Could not resolve window function '$name'. " +
+              "Note that, using window functions currently requires a HiveContext")
+
           case w @ WindowExpression(windowFunction, windowSpec) if windowSpec.validate.nonEmpty =>
             // The window spec is not valid.
             val reason = windowSpec.validate.get

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/AnalysisSuite.scala

@@ -166,6 +166,19 @@ class AnalysisSuite extends FunSuite with BeforeAndAfter {
     }
   }
 
+  errorTest(
+    "unresolved window function",
+    testRelation2.select(
+      WindowExpression(
+        UnresolvedWindowFunction(
+          "lead",
+          UnresolvedAttribute("c") :: Nil),
+        WindowSpecDefinition(
+          UnresolvedAttribute("a") :: Nil,
+          SortOrder(UnresolvedAttribute("b"), Ascending) :: Nil,
+          UnspecifiedFrame)).as('window)),
+      "lead" :: "window functions currently requires a HiveContext" :: Nil)
+
   errorTest(
     "too many generators",
     listRelation.select(Explode('list).as('a), Explode('list).as('b)),