Generate SerialName mapping functions for serializable enums

Author: ephemient

processor/src/main/kotlin/EnumSerialNamesProcessor.kt

@@ -0,0 +1,81 @@
+package com.github.ephemient.kotlinx.serialization.contrib.processor
+
+import com.google.auto.service.AutoService
+import com.google.devtools.ksp.KspExperimental
+import com.google.devtools.ksp.getAnnotationsByType
+import com.google.devtools.ksp.processing.Dependencies
+import com.google.devtools.ksp.processing.Resolver
+import com.google.devtools.ksp.processing.SymbolProcessor
+import com.google.devtools.ksp.processing.SymbolProcessorEnvironment
+import com.google.devtools.ksp.processing.SymbolProcessorProvider
+import com.google.devtools.ksp.symbol.ClassKind
+import com.google.devtools.ksp.symbol.KSAnnotated
+import com.google.devtools.ksp.symbol.KSClassDeclaration
+import com.squareup.kotlinpoet.FileSpec
+import com.squareup.kotlinpoet.FunSpec
+import com.squareup.kotlinpoet.STRING
+import com.squareup.kotlinpoet.ksp.KotlinPoetKspPreview
+import com.squareup.kotlinpoet.ksp.toClassName
+import com.squareup.kotlinpoet.ksp.writeTo
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+class EnumSerialNamesProcessor(environment: SymbolProcessorEnvironment) : SymbolProcessor {
+    private val codeGenerator = environment.codeGenerator
+
+    @OptIn(KotlinPoetKspPreview::class, KspExperimental::class)
+    override fun process(resolver: Resolver): List<KSAnnotated> {
+        for (enum in resolver.getSymbolsWithAnnotation(Serializable::class.qualifiedName!!, false)) {
+            if (enum !is KSClassDeclaration || enum.classKind != ClassKind.ENUM_CLASS) continue
+            val enumClass = enum.asStarProjectedType().toClassName()
+
+            val entries = enum.declarations
+                .filterIsInstance<KSClassDeclaration>()
+                .filter { it.classKind == ClassKind.ENUM_ENTRY }
+                .associate { entry ->
+                    val name = entry.simpleName.asString()
+                    val serialName = entry.getAnnotationsByType(SerialName::class)
+                        .firstNotNullOfOrNull { it.value.ifEmpty { null } }
+                    name to (serialName ?: name)
+                }
+
+            FileSpec.builder(enumClass.packageName, enumClass.simpleNames.joinToString("_", postfix = "SerialNames"))
+                .addFunction(
+                    FunSpec.builder("toSerialName")
+                        .receiver(enumClass)
+                        .returns(STRING)
+                        .beginControlFlow("return when (this)")
+                        .apply {
+                            for ((name, serialName) in entries) {
+                                addStatement("%T.%N -> %S", enumClass, name, serialName)
+                            }
+                        }
+                        .endControlFlow()
+                        .build()
+                )
+                .addFunction(
+                    FunSpec.builder(enumClass.simpleNames.joinToString("", "fromSerialNameTo", "OrNull"))
+                        .receiver(STRING)
+                        .returns(enumClass.copy(nullable = true))
+                        .beginControlFlow("return when (this)")
+                        .apply {
+                            for ((name, serialName) in entries) {
+                                addStatement("%S -> %T.%N", serialName, enumClass, name)
+                            }
+                        }
+                        .addStatement("else -> null")
+                        .endControlFlow()
+                        .build()
+                )
+                .build()
+                .writeTo(codeGenerator, Dependencies(false, *listOfNotNull(enum.containingFile).toTypedArray()))
+        }
+        return emptyList()
+    }
+
+    @AutoService(SymbolProcessorProvider::class)
+    class Provider : SymbolProcessorProvider {
+        override fun create(environment: SymbolProcessorEnvironment): SymbolProcessor =
+            EnumSerialNamesProcessor(environment)
+    }
+}

test/src/commonMain/kotlin/Example.kt

@@ -19,4 +19,6 @@ enum class Example {
     @SerialName("FORCE")
     Force,
     ;
+
+    override fun toString(): String = toSerialName()
 }