Lazy load UNIT_TYPE

[orangy]

Use case
We often use ObjectMapper for just json parsing and not full object mapping. Initialization of KotlinAnnotationIntrospector currently causes a delay because of Kotlin Reflection loading. We would like to eliminate this delay until it is really needed.

Describe the solution you'd like
Replace

        val UNIT_TYPE: KType = Unit::class.createType()

with

        val UNIT_TYPE: KType by lazy { Unit::class.createType() }

Describe alternatives you've considered
Alternative would be avoiding creating UNIT_TYPE altogther and replacing single usage returnType == UNIT_TYPE with checking FQN since it is well-known.

[sarbyn]

We got some ANR on our Android App (mainly on old devices) related to this issue, during Dagger init.

The stack trace is the following:

main (runnable):tid=1 systid=26675 
       at kotlin.reflect.jvm.internal.impl.serialization.deserialization.descriptors.DeserializedClassDescriptor$DeserializedClassTypeConstructor.getParameters(DeserializedClassDescriptor.kt:281)
       at kotlin.reflect.full.KClassifiers.createType(KClassifiers.kt:52)
       at kotlin.reflect.full.KClassifiers.createType$default(KClassifiers.java:43)
       at com.fasterxml.jackson.module.kotlin.KotlinAnnotationIntrospector.<clinit>(KotlinAnnotationIntrospector.kt:170)
       at com.fasterxml.jackson.module.kotlin.KotlinModule.setupModule(KotlinModule.kt:121)
       at com.fasterxml.jackson.databind.ObjectMapper.registerModule(ObjectMapper.java:853)
       [...]
       

Kotlin 1.5.31
Jackson 2.13.1

We will update kotlin, jackson to the latest versions and we will also use Dagger lazy inject, but I think it could be better to fix also on Jackson side. (I can do a Pull request if needed)

[cowtowncoder]

Note: 2.13 branch is unlikely to get new patches so I would strongly recommend seeing whether 2.14(.1) might help here. And if you do that maybe add a note (I am not saying there is a fix just that sometimes newer versions do have relevant fixes).