Fix duplicated field rejection for JSON codecs of records (#765)

Author: plokhotnyuk

zio-schema-json/shared/src/main/scala/zio/schema/codec/JsonCodec.scala

@@ -1002,7 +1002,7 @@ object JsonCodec {
       val rejectAdditionalFields = schema.annotations.exists(_.isInstanceOf[rejectExtraFields])
       (trace: List[JsonError], in: RetractReader) => {
         Lexer.char(trace, in, '{')
-        val map      = defaults.clone().asInstanceOf[util.HashMap[String, Any]]
+        val map      = new util.HashMap[String, Any]
         var continue = Lexer.firstField(trace, in)
         while (continue) {
           val fieldNameOrAlias = Lexer.string(trace, in).toString
@@ -1013,7 +1013,10 @@ object JsonCodec {
             val trace_ = span :: trace
             Lexer.char(trace_, in, ':')
             val fieldName = span.field
-            map.put(fieldName, dec.unsafeDecode(trace_, in))
+            val prev      = map.put(fieldName, dec.unsafeDecode(trace_, in))
+            if (prev != null) {
+              throw UnsafeJson(JsonError.Message("duplicate") :: trace)
+            }
           } else if (rejectAdditionalFields) {
             throw UnsafeJson(JsonError.Message(s"unexpected field: $fieldNameOrAlias") :: trace)
           } else {
@@ -1022,6 +1025,11 @@ object JsonCodec {
           }
           continue = Lexer.nextField(trace, in)
         }
+        val it = defaults.entrySet().iterator()
+        while (it.hasNext) {
+          val entry = it.next()
+          map.putIfAbsent(entry.getKey, entry.getValue)
+        }
         (ListMap.newBuilder[String, Any] ++= ({                         // to avoid O(n) insert operations
           import scala.collection.JavaConverters.mapAsScalaMapConverter // use deprecated class for Scala 2.12 compatibility
 

zio-schema-json/shared/src/test/scala/zio/schema/codec/JsonCodecSpec.scala

@@ -708,6 +708,18 @@ object JsonCodecSpec extends ZIOSpecDefault {
           charSequenceToByteChunk("""{"$f1":"test", "extraField":"extra"}""")
         ).flip.map(err => assertTrue(err.getMessage() == "(unexpected field: extraField)"))
       },
+      test("reject duplicated fields") {
+        assertDecodesToError(
+          recordSchema,
+          """{"foo":"test","bar":10,"foo":10}""",
+          JsonError.Message("duplicate") :: Nil
+        ) &>
+          assertDecodesToError(
+            recordSchema,
+            """{"bar":10,"foo":"test","bar":"100"}""",
+            JsonError.Message("duplicate") :: Nil
+          )
+      },
       test("optional field with schema or annotated default value") {
         assertDecodes(
           RecordExampleWithOptField.schema,
@@ -812,6 +824,18 @@ object JsonCodecSpec extends ZIOSpecDefault {
             JsonError.Message("extra field") :: Nil
           )
       },
+      test("reject duplicated fields") {
+        assertDecodesToError(
+          personSchema,
+          """{"name":"test","age":10,"name":10}""",
+          JsonError.Message("duplicate") :: Nil
+        ) &>
+          assertDecodesToError(
+            personSchema,
+            """{"age":10,"name":"test","age":"100"}""",
+            JsonError.Message("duplicate") :: Nil
+          )
+      },
       test("transient field annotation with default value in class definition") {
         assertDecodes(
           searchRequestWithTransientFieldSchema,