This is a release candidate for the next version. It is based on Kotlin 2.1.0 and includes a few new features, as well
as bugfixes and improvements:
@JsonIgnoreUnknownKeys annotation
Previously, only global setting JsonBuilder.ignoreUnknownKeys controlled whether Json parser would throw exception if input contained a property that was not declared in a @Serializable class. There were a lot of complaints that this setting is not flexible enough. To address them, we added new @JsonIgnoreUnknownKeys annotation that can be applied on a per-class basis. With this annotation, it is possible to allow unknown properties for annotated classes, while general decoding methods (such as Json.decodeFromString and others) would still reject them for everything else. See details in the corresponding PR.
Stabilization of SerialDescriptor API and @SealedSerializationApi annotation
SerialDescriptor, SerialKind, and related API has been around for a long time and has proven itself useful. The main reason @ExperimentalSerializationApi was on SerialDescriptor's properties is that we wanted to discourage people from subclassing it. Fortunately, Kotlin 2.1 provides a special mechanism for such a case — SubclassOptInRequired. New kotlinx.serialization.SealedSerializationApi annotation designates APIs as public for use, but closed for implementation — the case for SerialDescriptor, which is a non-sealed interface for
technical reasons. Now you can use most of SerialDescriptor and its builders API without the need to opt-in into experimental
serialization API. See the PR for more details.
Note: All SerialKinds are stable API now, except PolymorphicKind — we may want to expand it in the future.
Generated Java 8's default method implementations in interfaces
TL;DR This change ensures better binary compatibility in the future for library. You should not experience any
difference from it.
kotlinx.serialization library contains a lot of interfaces with default method implementations. Historically, Kotlin compiled a synthetic DefaultImpls class for them. Starting from Kotlin 1.4, it was possible to compile them using as Java 8's default methods to ensure that new methods can still be added to interfaces without the need for implementors to recompile. To preserve binary compatibility with existing clients, a special all-compatbility mode is supported in compiler to generate both default methods and synthetic DefaultImpls class.
Now, kotlinx.serialization finally makes use of this all-compatibility mode, which potentially allows us to add new methods to interfaces such as SerialDescriptor, Encoder, Decoder, etc., without breaking existing clients. This change is expected to have no effect on existing clients, and no action from your side is required. Note that Kotlin 2.2 plans to enable all-compatibility mode by default.
Other bugfixes and improvements
- Correctly skip structures with Cbor.ignoreUnknownKeys setting (#2873) (thanks to ardune)
- Handle missing system property without NPE (#2867)
- Fixed keeping INSTANCE field and serializer function for serializable objects in R8 full mode (#2865)
- Correctly parse invalid numbers in JsonLiteral.long and other extensions (#2852)
- Correctly handle serial name conflict for different classes in SerializersModule.overwriteWith (#2856)
- Add inline reified version of encodeToString as a Json member to streamline the experience for newcomers. (#2853)
- Do not check kind or discriminator collisions for subclasses' polymorphic serializers if Json.classDiscriminatorMode
is set to NONE (#2833)