From c5c1aa6bc78b6ebc346befe9f4b434401a683a59 Mon Sep 17 00:00:00 2001
From: Jakob Odersky <jakob@driver.xyz>
Date: Fri, 29 Jun 2018 17:56:06 -0700
Subject: Make inclusion of None values as null optional

---
 CHANGELOG.md                                       |  7 ++-
 shared/src/main/scala/DerivedFormats.scala         | 19 ++++++--
 shared/src/test/scala/OptionFieldTests.scala       | 53 ++++++++++++++++++++++
 shared/src/test/scala/ProductTypeFormatTests.scala | 17 -------
 4 files changed, 74 insertions(+), 22 deletions(-)
 create mode 100644 shared/src/test/scala/OptionFieldTests.scala

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6bdcd86..bf4dbd7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+# Version 0.5.0
+
+None values are no longer written to objects by default. This is
+configurable by overriding `printNull` in DerivedFormats.
+
 # Version 0.4.7
 
  Upgrade Magnolia from 0.7.1-1 to 0.8.0-1.
@@ -5,7 +10,7 @@
 # Version 0.4.6
 
 - Fix a bug in the derivation macro that prevented deriving formats for
-  parameterized types. I.e. it is now possible to write derive the following:
+  parameterized types. I.e. it is now possible to derive the following:
   ```
   class A[B](b: B)
   implicit def fmt[B: JsonFormat] = jsonFormat[A]
diff --git a/shared/src/main/scala/DerivedFormats.scala b/shared/src/main/scala/DerivedFormats.scala
index 6ea7c4b..ccf48d1 100644
--- a/shared/src/main/scala/DerivedFormats.scala
+++ b/shared/src/main/scala/DerivedFormats.scala
@@ -13,13 +13,24 @@ trait DerivedFormats { self: BasicFormats =>
     * method can be overriden to use alternative naming conventions. */
   @inline def extractFieldName(paramName: String): String = paramName
 
+  /** Determines if `None` instances of options should be included in JSON output.
+    *
+    * By default, `None` values are ommitted entirely from resulting JSON
+    * objects. If overridden, they will be included as `null`s instead.
+    *
+    * Note that this has no effect in *reading* option types; undefined or null
+    * values are always converted to `None`. */
+  def printNull: Boolean = false
+
   def combine[T](ctx: CaseClass[JsonFormat, T]): JsonFormat[T] =
     new JsonFormat[T] {
       override def write(value: T): JsValue = {
-        val fields: Seq[(String, JsValue)] = ctx.parameters.map { param =>
-          extractFieldName(param.label) -> param.typeclass.write(
-            param.dereference(value)
-          )
+        val fields: Seq[(String, JsValue)] = ctx.parameters.collect {
+          case param
+              if !param.option || param.dereference(value) != None || printNull =>
+            extractFieldName(param.label) -> param.typeclass.write(
+              param.dereference(value)
+            )
         }
         JsObject(fields: _*)
       }
diff --git a/shared/src/test/scala/OptionFieldTests.scala b/shared/src/test/scala/OptionFieldTests.scala
new file mode 100644
index 0000000..8cabf25
--- /dev/null
+++ b/shared/src/test/scala/OptionFieldTests.scala
@@ -0,0 +1,53 @@
+package spray.json
+
+import org.scalatest._
+
+class OptionFieldTests
+    extends FlatSpec
+    with FormatTests {
+
+  case class Opt(x: Option[Int])
+
+  object HideNull extends DerivedJsonProtocol {
+    override def printNull = false
+    implicit val optFmt = jsonFormat[Opt]
+  }
+
+  object ShowNull extends DerivedJsonProtocol {
+    override def printNull = true
+    implicit val optFmt = jsonFormat[Opt]
+  }
+
+
+  "Option fields with some value" should behave like checkRoundtrip(
+    Opt(Some(2)),
+    """{"x":2}"""
+  )(HideNull.optFmt)
+
+  "Option fields with some value (show null)" should behave like checkRoundtrip(
+    Opt(Some(2)),
+    """{"x":2}"""
+  )(ShowNull.optFmt)
+
+  "Option fields with null value" should behave like checkRoundtrip(
+    Opt(None),
+    """{}"""
+  )(HideNull.optFmt)
+
+  "Option fields with null value (show null)" should behave like checkRoundtrip(
+    Opt(None),
+    """{"x":null}"""
+  )(ShowNull.optFmt)
+
+  "Option fields with undefined value" should "deserialize" in {
+    import HideNull._
+    assert("{}".parseJson.convertTo[Opt] == Opt(None))
+  }
+
+  "Option fields with undefined value (show null)" should "deserialize" in {
+    import ShowNull._
+    assert("{}".parseJson.convertTo[Opt] == Opt(None))
+  }
+
+}
+
diff --git a/shared/src/test/scala/ProductTypeFormatTests.scala b/shared/src/test/scala/ProductTypeFormatTests.scala
index 4c979c0..a869ac5 100644
--- a/shared/src/test/scala/ProductTypeFormatTests.scala
+++ b/shared/src/test/scala/ProductTypeFormatTests.scala
@@ -73,23 +73,6 @@ class ProductTypeFormatTests
     """{"h": {"x":true}}"""
   )
 
-  case class Opt(x: Option[Int])
-  implicit val optFmt = jsonFormat[Opt]
-
-  "Option fields with some value" should behave like checkRoundtrip(
-    Opt(Some(2)),
-    """{"x":2}"""
-  )
-
-  "Option fields with null value" should behave like checkRoundtrip(
-    Opt(None),
-    """{"x":null}"""
-  )
-
-  "Option fields with undefined value" should "deserialize" in {
-    assert("{}".parseJson.convertTo[Opt] == Opt(None))
-  }
-
   case class Typed[T](t: T)
 
   implicit def typed[T: JsonFormat] = jsonFormat[Typed[T]]
-- 
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