chore: Added test for the fix

Author: LichtHund

formats/hocon/src/main/kotlin/kotlinx/serialization/hocon/Hocon.kt

@@ -145,7 +145,7 @@ public sealed class Hocon(
 
     }
 
-    private inner class ConfigReader(val conf: Config, private val poly: Boolean = false) : ConfigConverter<String>() {
+    private inner class ConfigReader(val conf: Config, private val isPolymorph: Boolean = false) : ConfigConverter<String>() {
         private var ind = -1
 
         override fun decodeElementIndex(descriptor: SerialDescriptor): Int {
@@ -162,7 +162,7 @@ public sealed class Hocon(
             if (parentName.isEmpty()) childName else "$parentName.$childName"
 
         override fun SerialDescriptor.getTag(index: Int): String {
-            return if (!poly) composeName(
+            return if (!isPolymorph) composeName(
                 currentTagOrNull.orEmpty(),
                 getConventionElementName(index, useConfigNamingConvention)
             ) else getElementName(index)
@@ -216,7 +216,7 @@ public sealed class Hocon(
         override fun beginStructure(descriptor: SerialDescriptor): CompositeDecoder =
             when {
                 // Polymorph should always be object-like I believe?
-                descriptor.kind.objLike -> ConfigReader(conf, true)
+                descriptor.kind.objLike -> ConfigReader(conf, isPolymorph = true)
                 else -> this
             }
 

formats/hocon/src/test/kotlin/kotlinx/serialization/hocon/HoconPolymorphismTest.kt

@@ -23,6 +23,9 @@ class HoconPolymorphismTest {
         data class AnnotatedTypeChild(@SerialName("my_type") val type: String) : Sealed(3)
     }
 
+    @Serializable
+    data class SealedContainer(val sealed: Collection<Sealed>)
+
     @Serializable
     data class CompositeClass(var sealed: Sealed)
 
@@ -102,4 +105,25 @@ class HoconPolymorphismTest {
             serializer = Sealed.serializer(),
         )
     }
+
+    @Test
+    fun testCollectionContainer() {
+        objectHocon.assertStringFormAndRestored(
+            expected = """
+                sealed = [ 
+                    { type = annotated_type_child, my_type = override, intField = 3 }
+                    { type = object }
+                    { type = data_class, name = testDataClass, intField = 1 }
+                ]
+            """.trimIndent(),
+            original = SealedContainer(
+                listOf(
+                    Sealed.AnnotatedTypeChild(type = "override"),
+                    Sealed.ObjectChild,
+                    Sealed.DataClassChild(name = "testDataClass"),
+                )
+            ),
+            serializer = SealedContainer.serializer(),
+        )
+    }
 }