From 89edef530a3c9212ea595d1be07e3319f09d6685 Mon Sep 17 00:00:00 2001
From: Andriy Plokhotnyuk <plokhotnyuk@gmail.com>
Date: Wed, 29 Jan 2025 15:17:57 +0100
Subject: [PATCH] More efficient encoding of case classes

---
 .../src/main/scala-2.x/zio/json/macros.scala       | 14 ++++++++++----
 .../shared/src/main/scala-3/zio/json/macros.scala  |  6 +++++-
 .../scala/zio/json/internal/FieldEncoder.scala     |  4 ++--
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/zio-json/shared/src/main/scala-2.x/zio/json/macros.scala b/zio-json/shared/src/main/scala-2.x/zio/json/macros.scala
index 369bb1e8..23eb12f6 100644
--- a/zio-json/shared/src/main/scala-2.x/zio/json/macros.scala
+++ b/zio-json/shared/src/main/scala-2.x/zio/json/macros.scala
@@ -546,9 +546,15 @@ object DeriveJsonEncoder {
           var idx        = 0
           var prevFields = false // whether any fields have been written
           while (idx < fields.length) {
-            val field = fields(idx)
-            val p     = field.p.dereference(a)
-            field.encodeOrSkip(p) { () =>
+            val field   = fields(idx)
+            val p       = field.p.dereference(a)
+            val encoder = field.encoder
+            if (
+              (field.withExplicitNulls && field.withExplicitEmptyCollections) ||
+              (field.withExplicitNulls && !encoder.isEmpty(p)) ||
+              (field.withExplicitEmptyCollections && !encoder.isNothing(p)) ||
+              (!encoder.isEmpty(p) && !encoder.isNothing(p))
+            ) {
               // if we have at least one field already, we need a comma
               if (prevFields) {
                 out.write(',')
@@ -557,7 +563,7 @@ object DeriveJsonEncoder {
               JsonEncoder.string.unsafeEncode(field.name, indent_, out)
               if (indent.isEmpty) out.write(':')
               else out.write(" : ")
-              field.encoder.unsafeEncode(p, indent_, out)
+              encoder.unsafeEncode(p, indent_, out)
               prevFields = true // record that we have at least one field so far
             }
             idx += 1
diff --git a/zio-json/shared/src/main/scala-3/zio/json/macros.scala b/zio-json/shared/src/main/scala-3/zio/json/macros.scala
index 99f857f7..72c31b07 100644
--- a/zio-json/shared/src/main/scala-3/zio/json/macros.scala
+++ b/zio-json/shared/src/main/scala-3/zio/json/macros.scala
@@ -601,7 +601,11 @@ sealed class JsonEncoderDerivation(config: JsonCodecConfiguration) extends Deriv
           while (idx < fields.length) {
             val field = fields(idx)
             val p     = field.p.deref(a)
-            field.encodeOrSkip(p) { () =>
+            val encoder = field.encoder
+            if ((field.withExplicitNulls && field.withExplicitEmptyCollections) ||
+              (field.withExplicitNulls && !encoder.isEmpty(p)) ||
+              (field.withExplicitEmptyCollections && !encoder.isNothing(p)) ||
+              (!encoder.isEmpty(p) && !encoder.isNothing(p))) {
               // if we have at least one field already, we need a comma
               if (prevFields) {
                 out.write(',')
diff --git a/zio-json/shared/src/main/scala/zio/json/internal/FieldEncoder.scala b/zio-json/shared/src/main/scala/zio/json/internal/FieldEncoder.scala
index ac2cbc34..79183756 100644
--- a/zio-json/shared/src/main/scala/zio/json/internal/FieldEncoder.scala
+++ b/zio-json/shared/src/main/scala/zio/json/internal/FieldEncoder.scala
@@ -8,8 +8,8 @@ private[json] class FieldEncoder[T, P](
   val p: P,
   val name: String,
   val encoder: JsonEncoder[T],
-  withExplicitNulls: Boolean,
-  withExplicitEmptyCollections: Boolean
+  val withExplicitNulls: Boolean,
+  val withExplicitEmptyCollections: Boolean
 ) {
   private[this] val _encodeOrSkip: T => (() => Unit) => Unit =
     if (withExplicitNulls && withExplicitEmptyCollections) { _ => encode =>