allow toJson with star projections (#284)

Author: sargunv

geojson/src/commonMain/kotlin/org/maplibre/spatialk/geojson/GeoJson.kt

@@ -25,9 +25,9 @@ public data object GeoJson {
     public val jsonFormat: Json = Json {
         ignoreUnknownKeys = true
         serializersModule = SerializersModule {
-            polymorphicDefaultSerializer(GeoJsonObject::class) {
+            polymorphicDefaultSerializer(GeoJsonObject::class) { obj ->
                 val serializer =
-                    when (it) {
+                    when (obj) {
                         is Point -> Point.serializer()
                         is MultiPoint -> MultiPoint.serializer()
                         is LineString -> LineString.serializer()
@@ -39,7 +39,7 @@ public data object GeoJson {
                         is Feature<*, *> ->
                             Feature.serializer(
                                 Geometry.serializer().nullable,
-                                when (val props = it.properties) {
+                                when (val props = obj.properties) {
                                     is JsonObject? -> JsonObject.serializer().nullable
                                     else -> {
                                         @OptIn(InternalSerializationApi::class)
@@ -50,7 +50,7 @@ public data object GeoJson {
                         is FeatureCollection<*, *> ->
                             FeatureCollection.serializer(
                                 Geometry.serializer().nullable,
-                                when (val props = it.features.firstOrNull()?.properties) {
+                                when (val props = obj.features.firstNotNullOf { it.properties }) {
                                     is JsonObject? -> JsonObject.serializer().nullable
                                     else -> {
                                         @OptIn(InternalSerializationApi::class)

geojson/src/commonMain/kotlin/org/maplibre/spatialk/geojson/helpers.kt

@@ -3,6 +3,8 @@
 package org.maplibre.spatialk.geojson
 
 import kotlin.jvm.JvmSynthetic
+import kotlin.reflect.KTypeProjection
+import kotlin.reflect.typeOf
 import kotlinx.serialization.SerializationException
 import kotlinx.serialization.json.JsonObject
 
@@ -27,7 +29,14 @@ import kotlinx.serialization.json.JsonObject
  * @throws SerializationException if serialization fails.
  * @see GeoJson.encodeToString
  */
-public inline fun <reified T : GeoJsonObject> T.toJson(): String = GeoJson.encodeToString<T>(this)
+public inline fun <reified T : GeoJsonObject> T.toJson(): String {
+    // If the type is known at compile time (no star projections), use that serializer
+    return if (typeOf<T>().arguments.none { it == KTypeProjection.STAR })
+        GeoJson.encodeToString<T>(this)
+
+    // Otherwise, use runtime lookup (GeoJsonObject polymorphic default serializer)
+    else GeoJson.encodeToString<GeoJsonObject>(this)
+}
 
 /**
  * Marks GeoJSON API that should be used with caution.

geojson/src/commonTest/kotlin/org/maplibre/spatialk/geojson/FeatureTest.kt

@@ -508,10 +508,10 @@ class FeatureTest {
         // Map<*, *> properties not tested because the fallback serializer selection does not
         // support generic types.
 
-        val nullPropsFeature: GeoJsonObject = Feature(null, null)
-        val jsonObjectPropsFeature: GeoJsonObject =
+        val nullPropsFeature: Feature<*, *> = Feature(null, null)
+        val jsonObjectPropsFeature: Feature<*, *> =
             Feature(null, JsonObject(mapOf("key" to JsonPrimitive("value"))))
-        val dataClassPropsFeature: GeoJsonObject = Feature(null, NameProp("test"))
+        val dataClassPropsFeature: Feature<*, *> = Feature(null, NameProp("test"))
 
         val nullDeserialized = GeoJsonObject.fromJson(nullPropsFeature.toJson()) as Feature<*, *>
         val jsonObjectDeserialized =