From 7cc1d1efd4343b08cdaae1553a3813a54b58743e Mon Sep 17 00:00:00 2001
From: Thijs Broersen <mht.broersen@gmail.com>
Date: Fri, 28 Jun 2024 21:58:23 +0200
Subject: [PATCH] feat: string-like field-decoder

---
 .../src/main/scala/zio/json/JsonFieldDecoder.scala   | 12 +++++++++++-
 .../test/scala-3/zio/json/DerivedDecoderSpec.scala   |  8 +++++++-
 .../test/scala-3/zio/json/DerivedEncoderSpec.scala   |  5 +++++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/zio-json/shared/src/main/scala/zio/json/JsonFieldDecoder.scala b/zio-json/shared/src/main/scala/zio/json/JsonFieldDecoder.scala
index 68fc213cf..3d3201dee 100644
--- a/zio-json/shared/src/main/scala/zio/json/JsonFieldDecoder.scala
+++ b/zio-json/shared/src/main/scala/zio/json/JsonFieldDecoder.scala
@@ -40,7 +40,7 @@ trait JsonFieldDecoder[+A] {
   def unsafeDecodeField(trace: List[JsonError], in: String): A
 }
 
-object JsonFieldDecoder {
+object JsonFieldDecoder extends LowPriorityJsonFieldDecoder {
   def apply[A](implicit a: JsonFieldDecoder[A]): JsonFieldDecoder[A] = a
 
   implicit val string: JsonFieldDecoder[String] = new JsonFieldDecoder[String] {
@@ -65,3 +65,13 @@ object JsonFieldDecoder {
       }
     }
 }
+
+private[json] trait LowPriorityJsonFieldDecoder {
+
+  def string: JsonFieldDecoder[String]
+
+  private def quotedString = string.map(raw => s""""$raw"""")
+
+  implicit def stringLike[T <: String: JsonDecoder]: JsonFieldDecoder[T] =
+    quotedString.mapOrFail(implicitly[JsonDecoder[T]].decodeJson)
+}
diff --git a/zio-json/shared/src/test/scala-3/zio/json/DerivedDecoderSpec.scala b/zio-json/shared/src/test/scala-3/zio/json/DerivedDecoderSpec.scala
index b7b6379f0..46a5c05a3 100644
--- a/zio-json/shared/src/test/scala-3/zio/json/DerivedDecoderSpec.scala
+++ b/zio-json/shared/src/test/scala-3/zio/json/DerivedDecoderSpec.scala
@@ -51,6 +51,12 @@ object DerivedDecoderSpec extends ZIOSpecDefault {
 
       assertTrue("""{"aOrB": "A", "optA": "A"}""".fromJson[Foo] == Right(Foo("A", Some("A")))) &&
       assertTrue("""{"aOrB": "C"}""".fromJson[Foo] == Left(".aOrB(expected one of: A, B)"))
-    }
+    },
+    test("Derives and decodes for a custom map key string-based union type") {
+      case class Foo(aOrB: Map["A" | "B", Int]) derives JsonDecoder
+
+      assertTrue("""{"aOrB": {"A": 1, "B": 2}}""".fromJson[Foo] == Right(Foo(Map("A" -> 1, "B" -> 2)))) &&
+      assertTrue("""{"aOrB": {"C": 1}}""".fromJson[Foo] == Left(".aOrB.C((expected one of: A, B))"))
+    },
   )
 }
diff --git a/zio-json/shared/src/test/scala-3/zio/json/DerivedEncoderSpec.scala b/zio-json/shared/src/test/scala-3/zio/json/DerivedEncoderSpec.scala
index 2eb329c40..2c21a599b 100644
--- a/zio-json/shared/src/test/scala-3/zio/json/DerivedEncoderSpec.scala
+++ b/zio-json/shared/src/test/scala-3/zio/json/DerivedEncoderSpec.scala
@@ -49,6 +49,11 @@ object DerivedEncoderSpec extends ZIOSpecDefault {
       case class Foo(aOrB: "A" | "B", optA: Option["A"]) derives JsonEncoder
 
       assertTrue(Foo("A", Some("A")).toJson == """{"aOrB":"A","optA":"A"}""")
+    },
+    test("Derives and encodes for a custom map key string-based union type") {
+      case class Foo(aOrB: Map["A" | "B", Int]) derives JsonEncoder
+
+      assertTrue(Foo(Map("A" -> 1, "B" -> 2)).toJson == """{"aOrB":{"A":1,"B":2}}""")
     }
   )
 }