Generate json encoders for choice args/results (#18834)

* Generate json encoders for choice args/results

sdk/language-support/java/codegen/src/main/scala/com/digitalasset/daml/lf/codegen/backend/java/inner/DecoderClass.scala

@@ -85,7 +85,7 @@ object DecoderClass {
 
   private val decodersField = FieldSpec
     .builder(contractDecoderType, "contractDecoder")
-    .addModifiers(Modifier.PRIVATE, Modifier.STATIC, Modifier.FINAL)
+    .addModifiers(Modifier.PUBLIC, Modifier.STATIC, Modifier.FINAL)
     .build()
 
   def generateStaticInitializer(templateNames: Iterable[ClassName]): CodeBlock = {

sdk/language-support/java/codegen/src/main/scala/com/digitalasset/daml/lf/codegen/backend/java/inner/TemplateClass.scala

@@ -524,7 +524,7 @@ private[inner] object TemplateClass extends StrictLogging {
           Modifier.PUBLIC,
         )
         .initializer(
-          "$Z$T.create($>$S, value$$ -> $L,$Wvalue$$ ->$W$L,$Wvalue$$ ->$W$L,$W$L,$W$L)$<",
+          "$Z$T.create($>$S, value$$ -> $L,$Wvalue$$ ->$W$L,$Wvalue$$ ->$W$L,$W$L,$W$L,$W$L,$W$L)$<",
           fieldClass,
           choiceName,
           generateToValueConverter(
@@ -546,6 +546,8 @@ private[inner] object TemplateClass extends StrictLogging {
           ),
           FromJsonGenerator.jsonDecoderForType(choice.param),
           FromJsonGenerator.jsonDecoderForType(choice.returnType),
+          ToJsonGenerator.encoderOf(choice.param),
+          ToJsonGenerator.encoderOf(choice.returnType),
         )
         .build()
     }.toSeq

sdk/language-support/java/codegen/src/main/scala/com/digitalasset/daml/lf/codegen/backend/java/inner/ToJsonGenerator.scala

@@ -244,7 +244,7 @@ private[inner] object ToJsonGenerator {
     .returns(fieldClass)
     .build()
 
-  private def encoderOf(
+  private[inner] def encoderOf(
       damlType: Type,
       nesting: Int = 0, // Used to avoid clashing argument identifiers in nested encoder definitions
   )(implicit packagePrefixes: PackagePrefixes): CodeBlock = {

sdk/language-support/java/codegen/src/test/daml/Bar.daml

@@ -3,12 +3,24 @@
 
 module Bar where
 
+data Result = Result
+    with
+        result : Int
+    deriving (Eq, Show)
+
 template Bar
     with
         owner : Party
     where
         signatory owner
 
+        choice AddOne : Result
+            with
+                value : Int
+            controller owner
+            do
+                return Result with result = value + 1
+
 data ParameterizedContractId a = ParameterizedContractId
     with
         parameterizedContractId: ContractId a
@@ -20,4 +32,3 @@ template Haha
         owner : Party
     where
         signatory owner
-

sdk/language-support/java/codegen/src/test/scala/com/digitalasset/daml/lf/codegen/backend/java/ChoiceFieldsSpec.scala

@@ -5,9 +5,12 @@ package com.daml.lf.codegen.backend.java
 
 import com.daml.ledger.javaapi.data.Unit
 import com.daml.ledger.javaapi.data.codegen.Choice
+import com.daml.ledger.javaapi.data.codegen.json.JsonLfReader
 import org.scalatest.matchers.should.Matchers
 import org.scalatest.wordspec.AnyWordSpec
 import ut.bar.Bar
+import ut.bar.AddOne
+import ut.bar.Result
 import ut.da.internal.template.Archive
 
 import scala.jdk.CollectionConverters._
@@ -23,8 +26,30 @@ final class ChoiceFieldsSpec extends AnyWordSpec with Matchers {
       val choices = Bar.COMPANION.choices
       val names = choices.keySet()
 
-      choices.size() shouldBe 1
+      choices.size() shouldBe 2
-      names shouldBe Set("Archive").asJava
+      names shouldBe Set("Archive", "AddOne").asJava
+    }
+
+    "encode and decode choice arguments in json" in {
+      val choice: Choice[Bar, AddOne, Result] = Bar.CHOICE_AddOne
+      val dummyArg = new AddOne(4)
+      val encodedArg = choice.argJsonEncoder(dummyArg).intoString()
+
+      "{\"value\": \"4\"}" shouldBe encodedArg
+
+      val decodedArg = choice.argJsonDecoder.decode(new JsonLfReader(encodedArg))
+      dummyArg shouldBe decodedArg
+    }
+
+    "encode and decode choice results in json" in {
+      val choice: Choice[Bar, AddOne, Result] = Bar.CHOICE_AddOne
+      val dummyResult = new Result(5)
+      val encodedResult = choice.resultJsonEncoder(dummyResult).intoString()
+
+      "{\"result\": \"5\"}" shouldBe encodedResult
+
+      val decodedResult = choice.resultJsonDecoder.decode(new JsonLfReader(encodedResult))
+      dummyResult shouldBe decodedResult
     }
   }
 }