From 0128a1592bfc8ec51840d80c3d564d6241445385 Mon Sep 17 00:00:00 2001
From: Juliano Alves <von.juliano@gmail.com>
Date: Fri, 13 Sep 2024 17:48:45 +0100
Subject: [PATCH] generate empty collections for missing fields

---
 .../scala/zio/schema/codec/JsonCodec.scala    | 17 ++++++++---
 .../zio/schema/codec/JsonCodecSpec.scala      | 29 +++++++++++++++++++
 .../src/main/scala/zio/schema/Schema.scala    | 10 ++++++-
 3 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/zio-schema-json/shared/src/main/scala/zio/schema/codec/JsonCodec.scala b/zio-schema-json/shared/src/main/scala/zio/schema/codec/JsonCodec.scala
index ee9c14a3d..19aa3fc78 100644
--- a/zio-schema-json/shared/src/main/scala/zio/schema/codec/JsonCodec.scala
+++ b/zio-schema-json/shared/src/main/scala/zio/schema/codec/JsonCodec.scala
@@ -1523,12 +1523,21 @@ object JsonCodec {
       var i = 0
       while (i < len) {
         if (buffer(i) == null) {
-
-          if ((fields(i).optional || fields(i).transient) && fields(i).defaultValue.isDefined)
+          if ((fields(i).optional || fields(i).transient) && fields(i).defaultValue.isDefined) {
             buffer(i) = fields(i).defaultValue.get
-          else
-            buffer(i) = schemaDecoder(schemas(i)).unsafeDecodeMissing(spans(i) :: trace)
+          } else {
+            val schema = fields(i).schema match {
+              case l @ Schema.Lazy(_) => l.schema
+              case _                  => schemas(i)
+            }
 
+            schema match {
+              case collection: Schema.Collection[_, _] =>
+                buffer(i) = collection.empty
+              case _ =>
+                buffer(i) = schemaDecoder(schema).unsafeDecodeMissing(spans(i) :: trace)
+            }
+          }
         }
         i += 1
       }
diff --git a/zio-schema-json/shared/src/test/scala/zio/schema/codec/JsonCodecSpec.scala b/zio-schema-json/shared/src/test/scala/zio/schema/codec/JsonCodecSpec.scala
index 0d3e37175..65938a6ab 100644
--- a/zio-schema-json/shared/src/test/scala/zio/schema/codec/JsonCodecSpec.scala
+++ b/zio-schema-json/shared/src/test/scala/zio/schema/codec/JsonCodecSpec.scala
@@ -1051,6 +1051,29 @@ object JsonCodecSpec extends ZIOSpecDefault {
         )
       }
     ),
+    suite("Missing collection fields")(
+      test("map") {
+        assertDecodes(
+          Schema[ListAndMap],
+          ListAndMap(Nil, Map.empty),
+          charSequenceToByteChunk("""{"list":[]}""")
+        )
+      },
+      test("list") {
+        assertDecodes(
+          Schema[ListAndMap],
+          ListAndMap(Nil, Map.empty),
+          charSequenceToByteChunk("""{"map":{}}""")
+        )
+      },
+      test("set") {
+        assertDecodes(
+          Schema[SetWrapper],
+          SetWrapper(Set.empty),
+          charSequenceToByteChunk("""{}""")
+        )
+      }
+    ),
     suite("zio.json.ast.Json decoding")(
       test("Json.Obj") {
         assertDecodes(
@@ -2172,6 +2195,12 @@ object JsonCodecSpec extends ZIOSpecDefault {
     implicit lazy val schema: Schema[ListAndMapAndOption] = DeriveSchema.gen[ListAndMapAndOption]
   }
 
+  final case class SetWrapper(set: Set[String])
+
+  object SetWrapper {
+    implicit lazy val schema: Schema[SetWrapper] = DeriveSchema.gen[SetWrapper]
+  }
+
   final case class KeyWrapper(key: String)
 
   object KeyWrapper {
diff --git a/zio-schema/shared/src/main/scala/zio/schema/Schema.scala b/zio-schema/shared/src/main/scala/zio/schema/Schema.scala
index 59a0f617f..5fa6cf310 100644
--- a/zio-schema/shared/src/main/scala/zio/schema/Schema.scala
+++ b/zio-schema/shared/src/main/scala/zio/schema/Schema.scala
@@ -512,6 +512,7 @@ object Schema extends SchemaPlatformSpecific with SchemaEquality {
   sealed trait Collection[Col, Elem] extends Schema[Col] {
     def fromChunk: Chunk[Elem] => Col
     def toChunk: Col => Chunk[Elem]
+    def empty: Col
   }
 
   final case class Sequence[Col, Elem, I](
@@ -534,6 +535,7 @@ object Schema extends SchemaPlatformSpecific with SchemaEquality {
 
     override def toString: String = s"Sequence($elementSchema, $identity)"
 
+    override def empty: Col = Seq.empty[Elem].asInstanceOf[Col]
   }
 
   final case class Transform[A, B, I](
@@ -840,6 +842,7 @@ object Schema extends SchemaPlatformSpecific with SchemaEquality {
 
     override val toChunk: scala.collection.immutable.Map[K, V] => Chunk[(K, V)] = map => Chunk.fromIterable(map.toList)
 
+    override def empty: scala.collection.immutable.Map[K, V] = scala.collection.immutable.Map.empty[K, V]
   }
 
   final case class NonEmptyMap[K, V](
@@ -874,6 +877,8 @@ object Schema extends SchemaPlatformSpecific with SchemaEquality {
 
     override def makeAccessors(b: AccessorBuilder): b.Traversal[prelude.NonEmptyMap[K, V], (K, V)] =
       b.makeTraversal(self, keySchema <*> valueSchema)
+
+    override def empty: prelude.NonEmptyMap[K, V] = throw new IllegalArgumentException(s"NonEmptySequence $identity cannot be empty")
   }
 
   final case class NonEmptySequence[Col, Elm, I](
@@ -900,6 +905,8 @@ object Schema extends SchemaPlatformSpecific with SchemaEquality {
     override def makeAccessors(b: AccessorBuilder): b.Traversal[Col, Elm] = b.makeTraversal(self, elementSchema)
 
     override def toString: String = s"NonEmptySequence($elementSchema, $identity)"
+
+    override def empty: Col = throw new IllegalArgumentException(s"NonEmptySequence $identity cannot be empty")
   }
 
   final case class Set[A](elementSchema: Schema[A], override val annotations: Chunk[Any] = Chunk.empty)
@@ -923,6 +930,7 @@ object Schema extends SchemaPlatformSpecific with SchemaEquality {
 
     override val toChunk: scala.collection.immutable.Set[A] => Chunk[A] = Chunk.fromIterable(_)
 
+    override def empty: scala.collection.immutable.Set[A] = scala.collection.immutable.Set.empty[A]
   }
 
   final case class Dynamic(override val annotations: Chunk[Any] = Chunk.empty) extends Schema[DynamicValue] {
@@ -10240,4 +10248,4 @@ object Schema extends SchemaPlatformSpecific with SchemaEquality {
         type Field22 = F22
       }
   }
-}
+}
\ No newline at end of file