Add accessors for oneof's generated data classes

wire-golden-files/src/main/kotlin/squareup/wire/sealedoneof/SealedOneOfs.kt

@@ -129,11 +129,11 @@ public class SealedOneOfs private constructor(
   public companion object {
     @JvmField
     public val ADAPTER: ProtoAdapter<SealedOneOfs> = object : ProtoAdapter<SealedOneOfs>(
-      FieldEncoding.LENGTH_DELIMITED,
-      SealedOneOfs::class,
-      "type.googleapis.com/squareup.wire.sealedoneof.SealedOneOfs",
-      PROTO_2,
-      null,
+      FieldEncoding.LENGTH_DELIMITED, 
+      SealedOneOfs::class, 
+      "type.googleapis.com/squareup.wire.sealedoneof.SealedOneOfs", 
+      PROTO_2, 
+      null, 
       "squareup/wire/sealed_oneof.proto"
     ) {
       override fun encodedSize(`value`: SealedOneOfs): Int {
@@ -195,3 +195,12 @@ public class SealedOneOfs private constructor(
     public inline fun build(body: Builder.() -> Unit): SealedOneOfs = Builder().apply(body).build()
   }
 }
+
+public val SealedOneOfs.Value.first_value: SealedMessage?
+  get() = (this as? SealedOneOfs.Value.FirstValue)?.value
+
+public val SealedOneOfs.Value.second_value: String?
+  get() = (this as? SealedOneOfs.Value.SecondValue)?.value
+
+public val SealedOneOfs.Value.value_: Int?
+  get() = (this as? SealedOneOfs.Value.Value)?.value

wire-kotlin-generator/api/wire-kotlin-generator.api

@@ -10,6 +10,7 @@ public final class com/squareup/wire/kotlin/KotlinGenerator {
 	public static final field Companion Lcom/squareup/wire/kotlin/KotlinGenerator$Companion;
 	public synthetic fun <init> (Lcom/squareup/wire/schema/Schema;Ljava/util/Map;Ljava/util/Map;Lcom/squareup/wire/schema/Profile;ZZZZLcom/squareup/wire/kotlin/RpcCallStyle;Lcom/squareup/wire/kotlin/RpcRole;ILjava/lang/String;ZZLcom/squareup/wire/kotlin/EnumMode;Lcom/squareup/wire/kotlin/OneofMode;ZZZZLkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public final fun generateOptionType (Lcom/squareup/wire/schema/Extend;Lcom/squareup/wire/schema/Field;)Lcom/squareup/kotlinpoet/TypeSpec;
+	public final fun generateSealedOneOfAccessors (Lcom/squareup/wire/schema/Type;)Ljava/util/List;
 	public final fun generateServiceTypeSpecs (Lcom/squareup/wire/schema/Service;Lcom/squareup/wire/schema/Rpc;)Ljava/util/Map;
 	public static synthetic fun generateServiceTypeSpecs$default (Lcom/squareup/wire/kotlin/KotlinGenerator;Lcom/squareup/wire/schema/Service;Lcom/squareup/wire/schema/Rpc;ILjava/lang/Object;)Ljava/util/Map;
 	public final fun generateType (Lcom/squareup/wire/schema/Type;)Lcom/squareup/kotlinpoet/TypeSpec;

wire-kotlin-generator/src/main/java/com/squareup/wire/kotlin/KotlinGenerator.kt

@@ -338,6 +338,16 @@ class KotlinGenerator private constructor(
     }
   }
 
+  fun generateSealedOneOfAccessors(type: Type): List<PropertySpec> {
+    if (oneofMode != OneofMode.SEALED_CLASS) return listOf()
+
+    return when (type) {
+      is MessageType -> type.sealedOneOfAccessors()
+      is EnclosingType -> type.nestedTypes.flatMap(::generateSealedOneOfAccessors)
+      else -> listOf()
+    }
+  }
+
   /**
    * Generates all [TypeSpec]s for the given [Service].
    *
@@ -3063,6 +3073,53 @@ class KotlinGenerator private constructor(
     else -> boxedOneOfClassName(oneOf.name)
   }
 
+  /**
+   * Generates top-level extension properties that read values from sealed oneof instances.
+   *
+   * Example:
+   * ```
+   * public val PaymentMethodChoice.Method.card_id: String?
+   *   get() = (this as? PaymentMethodChoice.Method.CardId)?.value
+   *
+   * public val PaymentMethodChoice.Method.bank_account: BankAccount?
+   *   get() = (this as? PaymentMethodChoice.Method.BankAccount)?.value
+   * ```
+   */
+  private fun MessageType.sealedOneOfAccessors(): List<PropertySpec> {
+    val accessors = mutableListOf<PropertySpec>()
+    val className = typeName as ClassName
+    val nameAllocator = nameAllocator(this)
+
+    for (oneOf in sealedOneOfs()) {
+      val sealedClassName = className.nestedClass(nameAllocator[boxedOneOfClassName(oneOf.name)])
+      val subclassNameAllocator = sealedSubclassNameAllocator(oneOf)
+      val accessorNameAllocator = NameAllocator(preallocateKeywords = !escapeKotlinKeywords)
+
+      for (field in oneOf.fields) {
+        val fieldName = if (field.name == field.type!!.simpleName || hasEponymousType(schema, field)) {
+          accessorNameAllocator.newName(legacyQualifiedFieldName(field), field)
+        } else {
+          accessorNameAllocator.newName(field.name, field)
+        }
+        val subclassName = sealedClassName.nestedClass(subclassNameAllocator[field])
+        accessors += PropertySpec.builder(fieldName, field.type!!.typeName.copy(nullable = true))
+          .receiver(sealedClassName)
+          .getter(
+            FunSpec.getterBuilder()
+              .addStatement("return (this as? %T)?.value", subclassName)
+              .build(),
+          )
+          .build()
+      }
+    }
+
+    for (nestedType in nestedTypes) {
+      accessors += generateSealedOneOfAccessors(nestedType)
+    }
+
+    return accessors
+  }
+
   /**
    * Generates a sealed class for a oneof.
    *
@@ -3314,18 +3371,18 @@ class KotlinGenerator private constructor(
 
   private fun MessageType.flatOneOfs(): List<OneOf> = when (oneofMode) {
     OneofMode.FLAT -> oneOfs.filter { it.fields.size < boxOneOfsMinSize }
-    else -> emptyList()
+    else -> listOf()
   }
 
   private fun MessageType.boxOneOfs(): List<OneOf> = when (oneofMode) {
     OneofMode.FLAT -> oneOfs.filter { it.fields.size >= boxOneOfsMinSize }
     OneofMode.BOXED -> oneOfs
-    OneofMode.SEALED_CLASS -> emptyList()
+    OneofMode.SEALED_CLASS -> listOf()
   }
 
   private fun MessageType.sealedOneOfs(): List<OneOf> = when (oneofMode) {
     OneofMode.SEALED_CLASS -> oneOfs
-    else -> emptyList()
+    else -> listOf()
   }
 
   private fun sealedSubclassNameAllocator(oneOf: OneOf): NameAllocator = sealedSubclassNameAllocatorStore.getOrPut(oneOf) {
@@ -3545,7 +3602,7 @@ class KotlinGenerator private constructor(
             AnnotationTarget.FIELD,
           )
         METHOD_OPTIONS -> listOf(AnnotationTarget.FUNCTION)
-        else -> emptyList()
+        else -> listOf()
       }
 
     internal fun String.sanitizeKdoc(): String = this

wire-kotlin-generator/src/main/java/com/squareup/wire/kotlin/KotlinSchemaHandler.kt

@@ -19,6 +19,7 @@ import com.squareup.kotlinpoet.AnnotationSpec
 import com.squareup.kotlinpoet.AnnotationSpec.UseSiteTarget.FILE
 import com.squareup.kotlinpoet.ClassName
 import com.squareup.kotlinpoet.FileSpec
+import com.squareup.kotlinpoet.PropertySpec
 import com.squareup.kotlinpoet.TypeSpec
 import com.squareup.wire.schema.Extend
 import com.squareup.wire.schema.Field
@@ -143,12 +144,20 @@ class KotlinSchemaHandler(
     if (KotlinGenerator.builtInType(type.type)) return null
 
     val typeSpec = kotlinGenerator.generateType(type)
+    val topLevelProperties = kotlinGenerator.generateSealedOneOfAccessors(type)
     val className = kotlinGenerator.generatedTypeName(type)
-    return write(className, typeSpec, type.type, type.location, context)
+    return write(
+      className,
+      typeSpec,
+      type.type,
+      type.location,
+      context,
+      topLevelProperties = topLevelProperties,
+    )
   }
 
   override fun handle(service: Service, context: Context): List<Path> {
-    if (rpcRole === RpcRole.NONE) return emptyList()
+    if (rpcRole === RpcRole.NONE) return listOf()
 
     val generatedPaths = mutableListOf<Path>()
 
@@ -183,6 +192,7 @@ class KotlinSchemaHandler(
     source: Any,
     location: Location,
     context: Context,
+    topLevelProperties: List<PropertySpec> = listOf(),
   ): Path {
     val modulePath = context.outDirectory
     val kotlinFile = FileSpec.builder(name.packageName, name.simpleName)
@@ -198,14 +208,19 @@ class KotlinSchemaHandler(
           .build(),
       )
       .addType(typeSpec)
+      .apply {
+        for (propertySpec in topLevelProperties) {
+          addProperty(propertySpec)
+        }
+      }
       .build()
     val filePath = modulePath /
       kotlinFile.packageName.replace(".", "/") /
       "${kotlinFile.name}.kt"
 
     context.logger.artifactHandled(
       modulePath,
-      "${kotlinFile.packageName}.${(kotlinFile.members.first() as TypeSpec).name}",
+      "${kotlinFile.packageName}.${name.simpleName}",
       "Kotlin",
     )
     try {

wire-kotlin-generator/src/test/java/com/squareup/wire/kotlin/KotlinGeneratorTest.kt

@@ -2246,6 +2246,34 @@ class KotlinGeneratorTest {
     )
   }
 
+  @Test fun sealedOneofGeneratesFieldAccessors() {
+    val schema = buildSchema {
+      add(
+        "message.proto".toPath(),
+        """
+        |syntax = "proto2";
+        |message PaymentMethodChoice {
+        |  oneof method {
+        |    string card_id = 1;
+        |    int32 value = 2;
+        |  }
+        |}
+        """.trimMargin(),
+      )
+    }
+    val code = KotlinWithProfilesGenerator(schema)
+      .generateKotlin("PaymentMethodChoice", oneofMode = OneofMode.SEALED_CLASS)
+    assertThat(code).contains(
+      """
+      |public val PaymentMethodChoice.Method.card_id: String?
+      |  get() = (this as? PaymentMethodChoice.Method.CardId)?.value
+      |
+      |public val PaymentMethodChoice.Method.value_: Int?
+      |  get() = (this as? PaymentMethodChoice.Method.Value)?.value
+      """.trimMargin(),
+    )
+  }
+
   @Test fun sealedOneofGeneratesCamelCaseClassName() {
     val schema = buildSchema {
       add(

wire-kotlin-generator/src/test/java/com/squareup/wire/kotlin/KotlinWithProfilesGenerator.kt

@@ -70,6 +70,11 @@ internal class KotlinWithProfilesGenerator(private val schema: Schema) {
     val typeSpec = kotlinGenerator.generateType(type)
     val packageName = kotlinGenerator.generatedTypeName(type).packageName
     val fileSpec = FileSpec.builder(packageName, "_")
+      .apply {
+        for (propertySpec in kotlinGenerator.generateSealedOneOfAccessors(type)) {
+          addProperty(propertySpec)
+        }
+      }
       .addType(typeSpec)
       .addImport("com.squareup.wire.kotlin", "decodeMessage")
       .build()