From be4590d3d9ac4fcb6a81439eda527d0cb9b12200 Mon Sep 17 00:00:00 2001
From: Jisoo Park <jisoo.park@doomoolmori.com>
Date: Thu, 4 Jul 2024 12:31:13 +0900
Subject: [PATCH] Fix JSON decoding of empty objects

- discriminated case object
- case object with @rejectExtraField
---
 .../scala/zio/schema/codec/JsonCodec.scala    | 24 ++++++++++++++++++-
 .../zio/schema/codec/JsonCodecSpec.scala      | 16 ++++++++++++-
 2 files changed, 38 insertions(+), 2 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 b72d8af6d..1677ae64e 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
@@ -991,7 +991,29 @@ object JsonCodec {
     import JsonCodec.JsonDecoder.schemaDecoder
 
     private[codec] def caseClass0Decoder[Z](discriminator: Int, schema: Schema.CaseClass0[Z]): ZJsonDecoder[Z] = { (trace: List[JsonError], in: RetractReader) =>
-      if (discriminator == -1) Codecs.unitDecoder.unsafeDecode(trace, in)
+      val rejectExtraFields = schema.annotations.collectFirst({ case _: rejectExtraFields => () }).isDefined
+      var i = 0
+      def skipField(): Unit = {
+        if (rejectExtraFields) {
+          throw UnsafeJson(JsonError.Message("extra field") :: trace)
+        }
+        Lexer.char(trace, in, '"')
+        Lexer.skipString(trace, in)
+        Lexer.char(trace, in, ':')
+        Lexer.skipValue(trace, in)
+        i += 1
+      }
+
+      if (discriminator == -2) {
+        while (Lexer.nextField(trace, in)) { skipField() }
+      } else {
+        Lexer.char(trace, in, '{')
+        if (Lexer.firstField(trace, in)) {
+          skipField()
+          while (Lexer.nextField(trace, in)) { skipField() }
+        }
+      }
+
       schema.defaultConstruct()
     }
 
diff --git a/zio-schema-json/shared/src/test/scala-2/zio/schema/codec/JsonCodecSpec.scala b/zio-schema-json/shared/src/test/scala-2/zio/schema/codec/JsonCodecSpec.scala
index 115bee8e5..90494db94 100644
--- a/zio-schema-json/shared/src/test/scala-2/zio/schema/codec/JsonCodecSpec.scala
+++ b/zio-schema-json/shared/src/test/scala-2/zio/schema/codec/JsonCodecSpec.scala
@@ -524,7 +524,12 @@ object JsonCodecSpec extends ZIOSpecDefault {
           PersonWithRejectExtraFields.schema,
           """{"name":"test","age":10,"extraField":10}""",
           JsonError.Message("extra field") :: Nil
-        )
+        ) &>
+          assertDecodesToError(
+            CaseClass0WithRejectExtraFields.schema,
+            """{"extraField":10}""",
+            JsonError.Message("extra field") :: Nil
+          )
       },
       test("transient field annotation") {
         assertDecodes(
@@ -1242,6 +1247,9 @@ object JsonCodecSpec extends ZIOSpecDefault {
         assertEncodesThenDecodes(Schema[Command], Command.Cash) &>
           assertEncodesThenDecodes(Schema[Command], Command.Buy(100))
       },
+      test("decode discriminated case objects in array")(
+        assertDecodes(Schema[List[Command]], Command.Cash :: Nil, charSequenceToByteChunk("""[{"type":"Cash"}]"""))
+      ),
       suite("of case objects")(
         test("without annotation")(
           assertEncodesThenDecodes(Schema[Color], Color.Red)
@@ -1593,6 +1601,12 @@ object JsonCodecSpec extends ZIOSpecDefault {
 
     val schema: Schema[PersonWithRejectExtraFields] = DeriveSchema.gen[PersonWithRejectExtraFields]
   }
+
+  @rejectExtraFields final case class CaseClass0WithRejectExtraFields()
+  object CaseClass0WithRejectExtraFields {
+    val schema: Schema[CaseClass0WithRejectExtraFields] = DeriveSchema.gen[CaseClass0WithRejectExtraFields]
+  }
+
   case class FieldDefaultValueSearchRequest(
     query: String,
     pageNumber: Int,