Broken Kotlin 1.4 support in 2.13.2

[Spikhalskiy]

Actual

Using Kotlin 1.4.32 and Jackson 2.13.2.20220324 with jackson-module-kotlin I'm getting an exception

Caused by: java.lang.NoSuchMethodError: 'boolean kotlin.reflect.KClass.isValue()'
	at com.fasterxml.jackson.module.kotlin.KotlinAnnotationIntrospector.findSerializer(KotlinAnnotationIntrospector.kt:88)
	at com.fasterxml.jackson.module.kotlin.KotlinAnnotationIntrospector.findSerializer(KotlinAnnotationIntrospector.kt:26)
	at com.fasterxml.jackson.databind.introspect.AnnotationIntrospectorPair.findSerializer(AnnotationIntrospectorPair.java:334)
	at com.fasterxml.jackson.databind.introspect.AnnotationIntrospectorPair.findSerializer(AnnotationIntrospectorPair.java:334)
	at com.fasterxml.jackson.databind.ser.BasicSerializerFactory.findSerializerFromAnnotation(BasicSerializerFactory.java:540)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory._constructWriter(BeanSerializerFactory.java:862)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.findBeanProperties(BeanSerializerFactory.java:630)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.constructBeanOrAddOnSerializer(BeanSerializerFactory.java:401)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.findBeanOrAddOnSerializer(BeanSerializerFactory.java:294)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory._createSerializer2(BeanSerializerFactory.java:239)
	at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.createSerializer(BeanSerializerFactory.java:173)
	at com.fasterxml.jackson.databind.SerializerProvider._createUntypedSerializer(SerializerProvider.java:1495)
	at com.fasterxml.jackson.databind.SerializerProvider._createAndCacheUntypedSerializer(SerializerProvider.java:1443)
	at com.fasterxml.jackson.databind.SerializerProvider.findValueSerializer(SerializerProvider.java:544)
	at com.fasterxml.jackson.databind.SerializerProvider.findTypedValueSerializer(SerializerProvider.java:822)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:308)
	at com.fasterxml.jackson.databind.ObjectMapper._writeValueAndClose(ObjectMapper.java:4568)
	at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsBytes(ObjectMapper.java:3844)

The same code works fine with Jackson 2.13.1

The regression is introduced in #527
kotlin.reflect.KClass.isValue() was added in Kotlin 1.5 and not available in 1.4: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.reflect/-k-class/is-value.html

Expected

• get Kotlin 1.4 support back (the last release of 1.4 was not that long time ago to consider it end of life https://github.com/JetBrains/kotlin/releases/tag/v1.4.32) or
• explicitly state which versions of kotlin are supported by this module and that Kotlin 1.4 got dropped in 2.13.2. Jackson Kotlin Module's release notes are stating: "No changes since 2.13.1?" for 2.13.2.

[cowtowncoder]

Hmmmh. I wonder if the expected baseline is documented anywhere? 2.13(.2) seems to depend on Kotlin 1.5.30.

I do agree that baseline changes should not occur in patches, just trying to figure out what the baseline is expected to be: and suggest adding explicit definition.

[Spikhalskiy]

No, there is no official published end-of-life schedule for Kotlin versions.

For our project, I decided that if the minor version got an update in the last two years - it's still alive. But it's just our own made-up criteria. 1.4 is still alive according to it, 1.3 is not.
Another criteria/clue that may be used is that Kotlin 1.5 (and 1.6) gradle plugins got fixes to work correctly on Java 16 while 1.4 never did.

But it's definitely a good idea to establish a watermark and test against minor versions above this watermark.
For example, we test Temporal Java/Kotlin SDK against 1.4, 1.5 and 1.6 separately. And especially because some internals change between versions, kotlin reflection code has to have kotlin version condition checks sometimes. So it needs to be tested that our reflection code doesn't work only on 1.5/1.6.

[cowtowncoder]

While I am not the maintainer of this module, I think a PR to make 2.13(.3) work again would be accepted if (but only if) it could be done without reverting fix/change of #527.
I don't know if this is possible or not.

[Spikhalskiy]

Well, there are no value classes in Kotlin 1.4. So, the check for isValue() should be just replaced to (isKotlin15OrHigher() && isValue()) and we should be fine without breaking the new functionality for value classes.

[cowtowncoder]

Ok. Then a PR would be acceptable I think. I don't think I'll be able to do that but could probably code review and merge it.

[Spikhalskiy]

It also looks like the project builds against 1.6.10 now in 2.14. It may be not the best approach. Kotlin mostly guarantees binary compatibility with runtimes one minor version lower than the kotlin version that was used for the build. So, the 2.14 branch being released today will be fine on 1.6.x, should be fine on 1.5.x, but no guarantees on 1.4.x.

See https://kotlinlang.org/docs/kotlin-evolution.html#evolving-the-binary-format for reference.

All binaries are backwards compatible, i.e. a newer compiler can read older binaries (e.g. 1.3 understands 1.0 through 1.2),

Older compilers reject binaries that rely on new features (e.g. a 1.0 compiler rejects binaries that use coroutines).

Preferably (but we can't guarantee it), the binary format is mostly forwards compatible with the next feature release, but not later ones (in the cases when new features are not used, e.g. 1.3 can understand most binaries from 1.4, but not 1.5).

It's a good idea to use the lowest version of Kotlin that is actually needed for the project. It looks like for this module right now it's 1.5.x. I was able to downgrade 2.14 branch to Kotlin 1.5.32 mostly successfully (with one failed TestJacksonWithKotlin.findingFactoryMethod3 test).

It would be great if this project may be migrated to build on 1.5.32 for the sake of binary backward compatibility.

[cowtowncoder]

/cc @dinomite

[k163377]

@cowtowncoder @Spikhalskiy

official published end-of-life schedule for Kotlin versions

Unless there is a policy change, the three major versions (i.e., down to 1.4 at this time) will be supported from JetBrains.
The rationale is the following reference

To give you more time for migration, we support the development for three previous language and API versions in addition to the latest stable one.
https://kotlinlang.org/docs/kotlin-evolution.html#compatibility-flags

[Spikhalskiy]

Are there any plans for fixing this regression with Kotlin 1.4? We have to stick to 1.13.1 because of this.