[SPARK-12271][SQL] Improve error message when Dataset.as[ ] has incompatible schemas.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/ScalaReflection.scala

@@ -184,7 +184,7 @@ object ScalaReflection extends ScalaReflection {
         val TypeRef(_, _, Seq(optType)) = t
         val className = getClassNameFromType(optType)
         val newTypePath = s"""- option value class: "$className"""" +: walkedTypePath
-        WrapOption(constructorFor(optType, path, newTypePath))
+        WrapOption(constructorFor(optType, path, newTypePath), dataTypeFor(optType))
 
       case t if t <:< localTypeOf[java.lang.Integer] =>
         val boxedType = classOf[java.lang.Integer]

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/encoders/ExpressionEncoder.scala

@@ -251,6 +251,7 @@ case class ExpressionEncoder[T](
 
     val plan = Project(Alias(unbound, "")() :: Nil, LocalRelation(schema))
     val analyzedPlan = SimpleAnalyzer.execute(plan)
+    SimpleAnalyzer.checkAnalysis(analyzedPlan)
     val optimizedPlan = SimplifyCasts(analyzedPlan)
 
     // In order to construct instances of inner classes (for example those declared in a REPL cell),

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects.scala

@@ -23,11 +23,9 @@ import scala.reflect.ClassTag
 import org.apache.spark.SparkConf
 import org.apache.spark.serializer._
 import org.apache.spark.sql.Row
-import org.apache.spark.sql.catalyst.analysis.SimpleAnalyzer
-import org.apache.spark.sql.catalyst.plans.logical.{Project, LocalRelation}
-import org.apache.spark.sql.catalyst.util.GenericArrayData
 import org.apache.spark.sql.catalyst.InternalRow
-import org.apache.spark.sql.catalyst.expressions.codegen.{GeneratedExpressionCode, CodeGenContext}
+import org.apache.spark.sql.catalyst.expressions.codegen.{CodeGenContext, GeneratedExpressionCode}
+import org.apache.spark.sql.catalyst.util.GenericArrayData
 import org.apache.spark.sql.types._
 
 /**
@@ -295,13 +293,17 @@ case class UnwrapOption(
  * Converts the result of evaluating `child` into an option, checking both the isNull bit and
  * (in the case of reference types) equality with null.
  * @param child The expression to evaluate and wrap.
+ * @param optType The type of this option.
  */
-case class WrapOption(child: Expression) extends UnaryExpression {
+case class WrapOption(child: Expression, optType: DataType)
+  extends UnaryExpression with ExpectsInputTypes {
 
   override def dataType: DataType = ObjectType(classOf[Option[_]])
 
   override def nullable: Boolean = true
 
+  override def inputTypes: Seq[AbstractDataType] = optType :: Nil
+
   override def eval(input: InternalRow): Any =
     throw new UnsupportedOperationException("Only code-generated evaluation is supported")
 

sql/core/src/test/scala/org/apache/spark/sql/DatasetSuite.scala

@@ -481,10 +481,18 @@ class DatasetSuite extends QueryTest with SharedSQLContext {
     val ds = Seq(2 -> 2.toByte, 3 -> 3.toByte).toDF("a", "b").as[ClassData]
     assert(ds.collect().toSeq == Seq(ClassData("2", 2), ClassData("3", 3)))
   }
-}
 
+  test("verify mismatching field names fail with a good error") {
+    val ds = Seq(ClassData("a", 1)).toDS()
+    val e = intercept[AnalysisException] {
+      ds.as[ClassData2].collect()
+    }
+    assert(e.getMessage.contains("cannot resolve 'c' given input columns a, b"), e.getMessage)
+  }
+}
 
 case class ClassData(a: String, b: Int)
+case class ClassData2(c: String, d: Int)
 case class ClassNullableData(a: String, b: Integer)
 
 /**