Error is not correctly displayed for nested objects starting from 0.14.3

[alycklama]

I noticed that the error message is sometimes incorrect when decoding nested objects.

package org.my

import cats.implicits._
import io.circe.Decoder
import io.circe.parser.decode
import io.circe.generic.semiauto.deriveDecoder

object MyMain extends App {
  case class Location(city: String)
  case class Person(name: String, location: Location)

  val jsonString =
    """{
      | "name": "John",
      | "location": {
      | }
      |}""".stripMargin

  implicit val decoder: Decoder[Person] = deriveDecoder[Person]

  val result = decode[Person](jsonString)
  println(result)
  println(result.left.map(_.show))
}

For 0.14.2 it works as expected because it's clear where the missing property comes from (i.e. .location.city):

Left(DecodingFailure(Missing required field, List(DownField(city), DownField(location))))
Left(DecodingFailure at .location.city: Missing required field)

For 0.14.3 it doesn't work as expected as the root (.location) seems to be missing only in the .show:

Left(DecodingFailure(Missing required field, List(DownField(city), DownField(location))))
Left(DecodingFailure at .city: Missing required field)

For 0.14.4 and 0.14.5 the output is as follows where both miss the root object (i.e. .location):

Left(DecodingFailure at .city: Missing required field)
Left(DecodingFailure at .city: Missing required field)

[iyfedorov]

#2138

[zorba128]

see also #2248

[zarthross]

#2138 should fix this.

[alycklama]

I can confirm this issue seems to be resolved.

However, I need to add an additional decoder for Location to make it work.

Updated Code

package org.my

import cats.implicits._
import io.circe._
import io.circe.generic.semiauto._
import io.circe.parser.decode

object Main extends App {
  case class Location(city: String)
  case class Person(name: String, location: Location)

  val jsonString =
    """{
      | "name": "John",
      | "location": {
      | }
      |}""".stripMargin

  implicit val locationDecoder: Decoder[Location] = deriveDecoder[Location]
  implicit val personDecoder: Decoder[Person] = deriveDecoder[Person]

  val result = decode[Person](jsonString)
  println(result)
  println(result.left.map(_.show))
}

Output

Left(DecodingFailure at .location.city: Missing required field)
Left(DecodingFailure at .location.city: Missing required field)

Ommitting Location Decoder

For some reason, it's no longer possible to derive nested case classes. You'll end up with the error below:

Could not find Lazy implicit value of type io.circe.generic.decoding.DerivedDecoder[org.my.Main.Person]

I'll close this issue, as the issue has been resolved. It would be nice if the error was more precise, though. It's not the Person but the Location which could not be found.

[zarthross]

The behavior is as expected. 'semi-auto' derivation should not do nested case classes.