Fix missing field name in an error for duplicated fields (#768)

Author: plokhotnyuk

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

@@ -940,7 +940,7 @@ object JsonCodec {
             val fieldName = span.field
             val prev      = map.put(fieldName, dec.unsafeDecode(trace_, in))
             if (prev != null) {
-              throw UnsafeJson(JsonError.Message("duplicate") :: trace)
+              throw UnsafeJson(JsonError.Message("duplicate") :: trace_)
             }
           } else if (rejectAdditionalFields) {
             throw UnsafeJson(JsonError.Message(s"unexpected field: $fieldNameOrAlias") :: trace)
@@ -1499,8 +1499,9 @@ object JsonCodec {
         val idx = Lexer.field(trace, reader, stringMatrix)
         if (pos == discriminator) Lexer.skipValue(trace, reader)
         else if (idx >= 0) {
-          if (buffer(idx) != null) error(trace, "duplicate")
-          else buffer(idx) = fieldDecoders(idx).unsafeDecode(spans(idx) :: trace, reader)
+          val trace_ = spans(idx) :: trace
+          if (buffer(idx) != null) error(trace_, "duplicate")
+          else buffer(idx) = fieldDecoders(idx).unsafeDecode(trace_, reader)
         } else if (!rejectExtraFields) Lexer.skipValue(trace, reader)
         else error(trace, "extra field")
         continue = Lexer.nextField(trace, reader)

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

@@ -721,12 +721,12 @@ object JsonCodecSpec extends ZIOSpecDefault {
         assertDecodesToError(
           recordSchema,
           """{"foo":"test","bar":10,"foo":10}""",
-          JsonError.Message("duplicate") :: Nil
+          JsonError.Message("duplicate") :: JsonError.ObjectAccess("foo") :: Nil
         ) &>
           assertDecodesToError(
             recordSchema,
             """{"bar":10,"foo":"test","bar":"100"}""",
-            JsonError.Message("duplicate") :: Nil
+            JsonError.Message("duplicate") :: JsonError.ObjectAccess("bar") :: Nil
           )
       },
       test("optional field with schema or annotated default value") {
@@ -837,12 +837,12 @@ object JsonCodecSpec extends ZIOSpecDefault {
         assertDecodesToError(
           personSchema,
           """{"name":"test","age":10,"name":10}""",
-          JsonError.Message("duplicate") :: Nil
+          JsonError.Message("duplicate") :: JsonError.ObjectAccess("name") :: Nil
         ) &>
           assertDecodesToError(
             personSchema,
             """{"age":10,"name":"test","age":"100"}""",
-            JsonError.Message("duplicate") :: Nil
+            JsonError.Message("duplicate") :: JsonError.ObjectAccess("age") :: Nil
           )
       },
       test("transient field annotation with default value in class definition") {