Add support for objects in sealed classes (#194)

hoplite-core/src/main/kotlin/com/sksamuel/hoplite/decoder/DataClassDecoder.kt

@@ -8,11 +8,13 @@ import com.sksamuel.hoplite.DecoderContext
 import com.sksamuel.hoplite.Node
 import com.sksamuel.hoplite.ParameterMapper
 import com.sksamuel.hoplite.PrimitiveNode
+import com.sksamuel.hoplite.StringNode
 import com.sksamuel.hoplite.Undefined
 import com.sksamuel.hoplite.fp.ValidatedNel
 import com.sksamuel.hoplite.fp.flatMap
 import com.sksamuel.hoplite.fp.sequence
 import com.sksamuel.hoplite.isDefined
+import com.sksamuel.hoplite.simpleName
 import java.lang.IllegalArgumentException
 import java.lang.reflect.InvocationTargetException
 import kotlin.reflect.KClass
@@ -40,8 +42,14 @@ class DataClassDecoder : NullHandlingDecoder<Any> {
   ): ConfigResult<Any> {
 
     val klass = type.classifier as KClass<*>
-    if (klass.constructors.isEmpty())
+    if (klass.constructors.isEmpty()) {
+      val instance = klass.objectInstance
+      if (instance != null && node is StringNode && node.value == type.simpleName.substringAfter("$")) {
+        return instance.valid()
+      }
       return ConfigFailure.DataClassWithoutConstructor(klass).invalid()
+    }
+
     val constructor = klass.constructors.first()
 
     // we have a special case, which is a data class with a single field with the name 'value'.

hoplite-yaml/src/test/kotlin/com/sksamuel/hoplite/yaml/SealedClassDecoderTest.kt

@@ -13,6 +13,13 @@ sealed class Database {
 
 sealed class Lonely
 
+sealed class PoolingStrategy {
+  object ABI : PoolingStrategy()
+  data class Combo(val combo: List<PoolingStrategy>) : PoolingStrategy()
+  object Omni: PoolingStrategy()
+  object OsVersion : PoolingStrategy()
+}
+
 class SealedClassDecoderTest : FunSpec({
 
   test("sealed classes decoding") {
@@ -45,4 +52,27 @@ class SealedClassDecoderTest : FunSpec({
       "\n" +
       "        - 'lonely': Sealed class class com.sksamuel.hoplite.yaml.Lonely does not define any subclasses"
   }
+
+  test("object inside sealed class decoding"){
+    data class Config(val poolingStrategy: PoolingStrategy)
+    val config = ConfigLoader().loadConfigOrThrow<Config>("/sealed_class_with_object.yaml")
+    config.poolingStrategy shouldBe PoolingStrategy.OsVersion
+  }
+
+  test("list of object inside sealed class decoding"){
+    data class Config(val poolingStrategy: PoolingStrategy)
+    val config = ConfigLoader().loadConfigOrThrow<Config>("/sealed_class_with_list_of_objects.yaml")
+    config.poolingStrategy shouldBe PoolingStrategy.Combo(listOf(PoolingStrategy.Omni, PoolingStrategy.OsVersion))
+  }
+
+  test("should error for invalid value inside sealed class"){
+    data class Config(val poolingStrategy: PoolingStrategy)
+    shouldThrow<ConfigException> {
+      ConfigLoader().loadConfigOrThrow<Config>("/sealed_class_with_object_invalid_value.yaml")
+    }.message shouldBe "Error loading config because:\n" +
+      "\n" +
+      "    - Could not instantiate 'com.sksamuel.hoplite.yaml.`SealedClassDecoderTest\$1\$6\$Config`' because:\n" +
+      "\n" +
+      "        - 'poolingStrategy': Could not find appropriate subclass of class com.sksamuel.hoplite.yaml.PoolingStrategy: Tried com.sksamuel.hoplite.yaml.PoolingStrategy\$ABI, com.sksamuel.hoplite.yaml.PoolingStrategy\$Combo, com.sksamuel.hoplite.yaml.PoolingStrategy\$Omni, com.sksamuel.hoplite.yaml.PoolingStrategy\$OsVersion (/sealed_class_with_object_invalid_value.yaml:0:17)"
+  }
 })

hoplite-yaml/src/test/resources/sealed_class_with_list_of_objects.yaml

@@ -0,0 +1,2 @@
+poolingStrategy:
+  combo: [Omni, OsVersion]

hoplite-yaml/src/test/resources/sealed_class_with_object.yaml

@@ -0,0 +1 @@
+poolingStrategy: OsVersion

hoplite-yaml/src/test/resources/sealed_class_with_object_invalid_value.yaml

@@ -0,0 +1 @@
+poolingStrategy: Random