[SPARK-18717][SQL] Make code generation for Scala Map work with immut…

…able.Map also

## What changes were proposed in this pull request?

Fixes compile errors in generated code when user has case class with a `scala.collections.immutable.Map` instead of a `scala.collections.Map`. Since ArrayBasedMapData.toScalaMap returns the immutable version we can make it work with both.

## How was this patch tested?

Additional unit tests.

Author: Andrew Ray <ray.andrew@gmail.com>

Closes #16161 from aray/fix-map-codegen.

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

@@ -342,7 +342,7 @@ object ScalaReflection extends ScalaReflection {
 
         StaticInvoke(
           ArrayBasedMapData.getClass,
-          ObjectType(classOf[Map[_, _]]),
+          ObjectType(classOf[scala.collection.immutable.Map[_, _]]),
           "toScalaMap",
           keyData :: valueData :: Nil)
 

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

@@ -1120,8 +1120,20 @@ class DatasetSuite extends QueryTest with SharedSQLContext {
     // sizeInBytes is 2404280404, before the fix, it overflows to a negative number
     assert(sizeInBytes > 0)
   }
+
+  test("SPARK-18717: code generation works for both scala.collection.Map" +
+    " and scala.collection.imutable.Map") {
+    val ds = Seq(WithImmutableMap("hi", Map(42L -> "foo"))).toDS
+    checkDataset(ds.map(t => t), WithImmutableMap("hi", Map(42L -> "foo")))
+
+    val ds2 = Seq(WithMap("hi", Map(42L -> "foo"))).toDS
+    checkDataset(ds2.map(t => t), WithMap("hi", Map(42L -> "foo")))
+  }
 }
 
+case class WithImmutableMap(id: String, map_test: scala.collection.immutable.Map[Long, String])
+case class WithMap(id: String, map_test: scala.collection.Map[Long, String])
+
 case class Generic[T](id: T, value: Double)
 
 case class OtherTuple(_1: String, _2: Int)