Fix sealed subclass picking

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

@@ -11,6 +11,7 @@ import com.sksamuel.hoplite.fp.plus
 import com.sksamuel.hoplite.fp.sequence
 import com.sksamuel.hoplite.fp.valid
 import kotlin.reflect.KClass
+import kotlin.reflect.KFunction
 import kotlin.reflect.KType
 import kotlin.reflect.full.createType
 
@@ -61,7 +62,16 @@ class SealedClassDecoder : NullHandlingDecoder<Any> {
         } else null
 
         val results = kclass.sealedSubclasses
-          .sortedByDescending { subclass -> subclass.constructors.maxOfOrNull { it.parameters.size } ?: 0 }
+          .filter { subclass ->
+            subclass hasConstructorsWithArgumentsNumberLessOrEqualTo node.expectedNumberOfConstructorArguments
+          }
+          .sortedWith { subclass1, subclass2 ->
+            (
+              subclass1.numberOfMandatoryConstructorArguments.compareTo(subclass2.numberOfMandatoryConstructorArguments)
+                .takeUnless { it == 0 }
+                ?: subclass1.numberOfTotalConstructorArguments.compareTo(subclass2.numberOfTotalConstructorArguments)
+              ) * -1
+          }
           .map { DataClassDecoder().decode(node, it.createType(), context) }
 
         val success = results.firstOrNull { it.isValid() }
@@ -72,4 +82,18 @@ class SealedClassDecoder : NullHandlingDecoder<Any> {
       }
     }
   }
+
+  private val KClass<*>.numberOfTotalConstructorArguments
+    get() = constructors.maxOfOrNull { it.numberOfTotalArguments } ?: 0
+
+  private val KClass<*>.numberOfMandatoryConstructorArguments
+    get() = constructors.maxOfOrNull { it.numberOfMandatoryArguments } ?: 0
+
+  private infix fun KClass<*>.hasConstructorsWithArgumentsNumberLessOrEqualTo(number: Int) =
+    constructors.map { it.numberOfMandatoryArguments }.any { it <= number }
+
+  private val KFunction<*>.numberOfMandatoryArguments get() = parameters.filterNot { it.isOptional }.size
+  private val KFunction<*>.numberOfTotalArguments get() = parameters.size
+
+  private val Node.expectedNumberOfConstructorArguments get() = size.takeIf { it > 0 } ?: 1
 }

hoplite-hocon/src/test/kotlin/com/sksamuel/hoplite/hocon/SealedClassTest.kt

@@ -7,10 +7,20 @@ import io.kotest.matchers.shouldBe
 
 sealed class ClientAuthConfig {
   data class UrlUserPass(val url: String, val user: String, val password: Masked) : ClientAuthConfig()
+
+  data class ConfigWithOneDefaultValue(val otherStuff: String = "") : ClientAuthConfig()
+
+  data class ConfigWithTwoDefaultValues(val otherStuff: String = "", val anotherStuff: String = "") : ClientAuthConfig()
   data class Url(val url: String) : ClientAuthConfig()
 }
 
-data class DbConfig(val clientAuth: ClientAuthConfig, val clientNoAuth: ClientAuthConfig)
+data class DbConfig(
+  val clientAuth: ClientAuthConfig,
+  val clientNoAuth: ClientAuthConfig = ClientAuthConfig.ConfigWithOneDefaultValue(),
+  val clientWithOneSpecifiedValue: ClientAuthConfig,
+  val clientWithTwoSpecifiedValue: ClientAuthConfig,
+  val clientWithDefaultValues: ClientAuthConfig = ClientAuthConfig.ConfigWithOneDefaultValue(),
+)
 
 class SealedClassTest : FunSpec() {
   init {
@@ -22,6 +32,14 @@ class SealedClassTest : FunSpec() {
         password = Masked("3pass"),
       )
       config.clientNoAuth shouldBe ClientAuthConfig.Url(url = "1url")
+      config.clientWithOneSpecifiedValue shouldBe ClientAuthConfig.ConfigWithTwoDefaultValues(
+        otherStuff = "1url",
+      )
+      config.clientWithTwoSpecifiedValue shouldBe ClientAuthConfig.ConfigWithTwoDefaultValues(
+        otherStuff = "1url",
+        anotherStuff = "test"
+      )
+      config.clientWithDefaultValues shouldBe ClientAuthConfig.ConfigWithOneDefaultValue()
     }
   }
 }

hoplite-hocon/src/test/resources/sealed.conf

@@ -7,3 +7,12 @@ clientAuth {
 clientNoAuth {
     url = "1url"
 }
+
+clientWithOneSpecifiedValue {
+    otherStuff = "1url"
+}
+
+clientWithTwoSpecifiedValue {
+    otherStuff = "1url"
+    anotherStuff = "test"
+}