[SPARK-5371][SQL] Propagate types after function conversion, before futher resolution

Before it was possible for a query to flip back and forth from a resolved state, allowing resolution to propagate up before coercion had stabilized.  The issue was that `ResolvedReferences` would run after `FunctionArgumentConversion`, but before `PropagateTypes` had run.  This PR ensures we correctly `PropagateTypes` after any coercion has applied.

Author: Michael Armbrust <michael@databricks.com>

Closes #5278 from marmbrus/unionNull and squashes the following commits:

dc3581a [Michael Armbrust] [SPARK-5371][SQL] Propogate types after function conversion / before futher resolution

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

@@ -78,6 +78,7 @@ trait HiveTypeCoercion {
     FunctionArgumentConversion ::
     CaseWhenCoercion ::
     Division ::
+    PropagateTypes ::
     Nil
 
   /**

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicOperators.scala

@@ -80,7 +80,7 @@ case class Union(left: LogicalPlan, right: LogicalPlan) extends BinaryNode {
 
   override lazy val resolved: Boolean =
     childrenResolved &&
-    !left.output.zip(right.output).exists { case (l,r) => l.dataType != r.dataType }
+    left.output.zip(right.output).forall { case (l,r) => l.dataType == r.dataType }
 
   override def statistics: Statistics = {
     val sizeInBytes = left.statistics.sizeInBytes + right.statistics.sizeInBytes

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/SQLQuerySuite.scala

@@ -41,8 +41,32 @@ case class NestedArray1(a: NestedArray2)
  */
 class SQLQuerySuite extends QueryTest {
 
+  test("SPARK-5371: union with null and sum") {
+    val df = Seq((1, 1)).toDF("c1", "c2")
+    df.registerTempTable("table1")
+
+    val query = sql(
+      """
+        |SELECT
+        |  MIN(c1),
+        |  MIN(c2)
+        |FROM (
+        |  SELECT
+        |    SUM(c1) c1,
+        |    NULL c2
+        |  FROM table1
+        |  UNION ALL
+        |  SELECT
+        |    NULL c1,
+        |    SUM(c2) c2
+        |  FROM table1
+        |) a
+      """.stripMargin)
+    checkAnswer(query, Row(1, 1) :: Nil)
+  }
+
   test("explode nested Field") {
-    Seq(NestedArray1(NestedArray2(Seq(1,2,3)))).toDF.registerTempTable("nestedArray")
+    Seq(NestedArray1(NestedArray2(Seq(1, 2, 3)))).toDF.registerTempTable("nestedArray")
     checkAnswer(
       sql("SELECT ints FROM nestedArray LATERAL VIEW explode(a.b) a AS ints"),
       Row(1) :: Row(2) :: Row(3) :: Nil)