[SPARK-13067] [SQL] workaround for a weird scala reflection problem

A simple workaround to avoid getting parameter types when convert a
logical plan to json.

Author: Wenchen Fan <wenchen@databricks.com>

Closes #10970 from cloud-fan/reflection.

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

@@ -601,6 +601,20 @@ object ScalaReflection extends ScalaReflection {
     getConstructorParameters(t)
   }
 
+  /**
+   * Returns the parameter names for the primary constructor of this class.
+   *
+   * Logically we should call `getConstructorParameters` and throw away the parameter types to get
+   * parameter names, however there are some weird scala reflection problems and this method is a
+   * workaround to avoid getting parameter types.
+   */
+  def getConstructorParameterNames(cls: Class[_]): Seq[String] = {
+    val m = runtimeMirror(cls.getClassLoader)
+    val classSymbol = m.staticClass(cls.getName)
+    val t = classSymbol.selfType
+    constructParams(t).map(_.name.toString)
+  }
+
   def getClassFromType(tpe: Type): Class[_] = mirror.runtimeClass(tpe.erasure.typeSymbol.asClass)
 }
 
@@ -745,6 +759,12 @@ trait ScalaReflection {
   def getConstructorParameters(tpe: Type): Seq[(String, Type)] = {
     val formalTypeArgs = tpe.typeSymbol.asClass.typeParams
     val TypeRef(_, _, actualTypeArgs) = tpe
+    constructParams(tpe).map { p =>
+      p.name.toString -> p.typeSignature.substituteTypes(formalTypeArgs, actualTypeArgs)
+    }
+  }
+
+  protected def constructParams(tpe: Type): Seq[Symbol] = {
     val constructorSymbol = tpe.member(nme.CONSTRUCTOR)
     val params = if (constructorSymbol.isMethod) {
       constructorSymbol.asMethod.paramss
@@ -758,9 +778,6 @@ trait ScalaReflection {
         primaryConstructorSymbol.get.asMethod.paramss
       }
     }
-
-    params.flatten.map { p =>
-      p.name.toString -> p.typeSignature.substituteTypes(formalTypeArgs, actualTypeArgs)
-    }
+    params.flatten
   }
 }

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala

@@ -512,7 +512,7 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product {
   }
 
   protected def jsonFields: List[JField] = {
-    val fieldNames = getConstructorParameters(getClass).map(_._1)
+    val fieldNames = getConstructorParameterNames(getClass)
     val fieldValues = productIterator.toSeq ++ otherCopyArgs
     assert(fieldNames.length == fieldValues.length, s"${getClass.getSimpleName} fields: " +
       fieldNames.mkString(", ") + s", values: " + fieldValues.map(_.toString).mkString(", "))
@@ -560,7 +560,7 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product {
     case obj if obj.getClass.getName.endsWith("$") => "object" -> obj.getClass.getName
     // returns null if the product type doesn't have a primary constructor, e.g. HiveFunctionWrapper
     case p: Product => try {
-      val fieldNames = getConstructorParameters(p.getClass).map(_._1)
+      val fieldNames = getConstructorParameterNames(p.getClass)
       val fieldValues = p.productIterator.toSeq
       assert(fieldNames.length == fieldValues.length)
       ("product-class" -> JString(p.getClass.getName)) :: fieldNames.zip(fieldValues).map {