[SPARK-4791] [sql] Infer schema from case class with multiple constructors

Modified ScalaReflection.schemaFor to take primary constructor of Product when there are multiple constructors.  Added test to suite which failed before but works now.

Needed for [https://github.com/apache/spark/pull/3637]

CC: marmbrus

Author: Joseph K. Bradley <joseph@databricks.com>

Closes #3646 from jkbradley/sql-reflection and squashes the following commits:

796b2e4 [Joseph K. Bradley] Modified ScalaReflection.schemaFor to take primary constructor of Product when there are multiple constructors.  Added test to suite which failed before but works now.

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

@@ -118,7 +118,19 @@ trait ScalaReflection {
       case t if t <:< typeOf[Product] =>
         val formalTypeArgs = t.typeSymbol.asClass.typeParams
         val TypeRef(_, _, actualTypeArgs) = t
-        val params = t.member(nme.CONSTRUCTOR).asMethod.paramss
+        val constructorSymbol = t.member(nme.CONSTRUCTOR)
+        val params = if (constructorSymbol.isMethod) {
+          constructorSymbol.asMethod.paramss
+        } else {
+          // Find the primary constructor, and use its parameter ordering.
+          val primaryConstructorSymbol: Option[Symbol] = constructorSymbol.asTerm.alternatives.find(
+            s => s.isMethod && s.asMethod.isPrimaryConstructor)
+          if (primaryConstructorSymbol.isEmpty) {
+            sys.error("Internal SQL error: Product object did not have a primary constructor.")
+          } else {
+            primaryConstructorSymbol.get.asMethod.paramss
+          }
+        }
         Schema(StructType(
           params.head.map { p =>
             val Schema(dataType, nullable) =

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/ScalaReflectionSuite.scala

@@ -68,6 +68,10 @@ case class ComplexData(
 case class GenericData[A](
     genericField: A)
 
+case class MultipleConstructorsData(a: Int, b: String, c: Double) {
+  def this(b: String, a: Int) = this(a, b, c = 1.0)
+}
+
 class ScalaReflectionSuite extends FunSuite {
   import ScalaReflection._
 
@@ -253,4 +257,14 @@ class ScalaReflectionSuite extends FunSuite {
       Row(1, 1, 1, 1, 1, 1, true))
     assert(convertToCatalyst(data, dataType) === convertedData)
   }
+
+  test("infer schema from case class with multiple constructors") {
+    val dataType = schemaFor[MultipleConstructorsData].dataType
+    dataType match {
+      case s: StructType =>
+        // Schema should have order: a: Int, b: String, c: Double
+        assert(s.fieldNames === Seq("a", "b", "c"))
+        assert(s.fields.map(_.dataType) === Seq(IntegerType, StringType, DoubleType))
+    }
+  }
 }