1 files changed, 47 insertions, 0 deletions
diff --git a/formats/hocon/src/main/kotlin/kotlinx/serialization/hocon/HoconDecoder.kt b/formats/hocon/src/main/kotlin/kotlinx/serialization/hocon/HoconDecoder.kt
new file mode 100644
index 00000000..a6006ff1
--- /dev/null
+++ b/formats/hocon/src/main/kotlin/kotlinx/serialization/hocon/HoconDecoder.kt
@@ -0,0 +1,47 @@
+package kotlinx.serialization.hocon
+
+import com.typesafe.config.Config
+import kotlinx.serialization.ExperimentalSerializationApi
+
+/**
+ * Decoder used by Hocon during deserialization.
+ * This interface allows to call methods from the Lightbend/config library on the [Config] object to intercept default deserialization process.
+ *
+ * Usage example (nested config serialization):
+ * ```
+ * @Serializable
+ * data class Example(
+ *   @Serializable(NestedConfigSerializer::class)
+ *   val d: Config
+ * )
+ * object NestedConfigSerializer : KSerializer<Config> {
+ *     override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("package.Config", PrimitiveKind.STRING)
+ *
+ *     override fun deserialize(decoder: Decoder): Config =
+ *         if (decoder is HoconDecoder) decoder.decodeConfigValue { conf, path -> conf.getConfig(path) }
+ *         else throw SerializationException("This class can be decoded only by Hocon format")
+ *
+ *     override fun serialize(encoder: Encoder, value: Config) {
+ *         if (encoder is AbstractHoconEncoder) encoder.encodeConfigValue(value.root())
+ *         else throw SerializationException("This class can be encoded only by Hocon format")
+ *     }
+ * }
+ *
+ * val nestedConfig = ConfigFactory.parseString("nested { value = \"test\" }")
+ * val globalConfig = Hocon.encodeToConfig(Example(nestedConfig)) // d: { nested: { value = "test" } }
+ * val newNestedConfig = Hocon.decodeFromConfig(Example.serializer(), globalConfig)
+ * ```
+ */
+@ExperimentalSerializationApi
+sealed interface HoconDecoder {
+
+    /**
+     * Decodes the value at the current path from the input.
+     * Allows to call methods on a [Config] instance.
+     *
+     * @param E type of value
+     * @param extractValueAtPath lambda for extracting value, where conf - original config object, path - current path expression being decoded.
+     * @return result of lambda execution
+     */
+    fun <E> decodeConfigValue(extractValueAtPath: (conf: Config, path: String) -> E): E
+}