Support Kotlin inline/value classes

[pswaminathan]

Suppose I have the following:

inline class Distance(val millimeters: Long): Comparable<Distance> {
    (truncated)
}

@JsonClass(generateAdapter = true)
data class ScratchEntity(val id: Int, val distance: Distance)

This compiles and works fine. But if I give any property a default value, e.g.

inline class Distance(val millimeters: Long): Comparable<Distance> {
    (truncated)
}

@JsonClass(generateAdapter = true)
data class ScratchEntity(val id: Int = 1, val distance: Distance)

I get the following traceback when trying to deserialize, e.g. {"id": 10, "distance": 20000}:

Exception in thread "main" java.lang.NoSuchMethodException: mypackage.ScratchEntity.<init>(int, mypackage.Distance, int, kotlin.jvm.internal.DefaultConstructorMarker)
	at java.lang.Class.getConstructor0(Class.java:3082)
	at java.lang.Class.getDeclaredConstructor(Class.java:2178)
	at mypackage.ScratchEntityJsonAdapter.fromJson(ScratchEntityJsonAdapter.kt:59)
	at mypackage.ScratchEntityJsonAdapter.fromJson(ScratchEntityJsonAdapter.kt:19)
	at com.squareup.moshi.JsonAdapter.fromJson(JsonAdapter.java:43)
	at org.jetbrains.kotlin.idea.scratch.generated.ScratchFileRunnerGenerated$ScratchFileRunnerGenerated.<init>(tmp.kt:24)
	at org.jetbrains.kotlin.idea.scratch.generated.ScratchFileRunnerGenerated.main(tmp.kt:30)

I suspect this is an interaction with inline classes: if I change to val distance: Int, all is good.

LMK if there is anything I can do to help diagnose or clarify!

[ZacSweers]

inline classes are not supported as they're not stable in kotlin itself yet

[pswaminathan]

Sure, and I'm not suggesting this requires an immediate fix—I have a work-around I can use for now for my own use cases. But as inline classes are an extremely useful feature, and ostensibly the goal is to support them as they become stable in Kotlin, it is worth tracking and understanding how, as inline classes evolve and become stable, this would/could be addressed. No?

[swankjesse]

Yep, when Kotlin has inline classes we’ll find a way to make ’em work nicely with Moshi.

[moomoomoo309]

Heads up, Kotlin 1.5 is stabilizing inline classes, and the stable functionality is available in 1.4.30 via a build.gradle switch.

[z3ntu]

Kotlin 1.5 is out! https://blog.jetbrains.com/kotlin/2021/05/kotlin-1-5-0-released/

[ZacSweers]

We should probably try to match how kotlinx-serialization treats them: https://youtrack.jetbrains.com/issue/KT-28791

PRs are welcome once #1339 merges and we update KotlinPoet. We will want to support this in both reflection and code gen, doesn't have to be the same PR but ideally we can reuse tests.

[ZacSweers]

kotlin-reflect itself doesn't support these either, so I think it will be awhile. https://youtrack.jetbrains.com/issue/KT-27598

[k163377]

Sharing regarding an update to a related issue.
The following issues have been resolved in kotlin-reflect 1.7.

https://youtrack.jetbrains.com/issue/KT-27598
https://youtrack.jetbrains.com/issue/KT-31141
https://youtrack.jetbrains.com/issue/KT-51804

[johnnyzen]

Any updates on supporting Kotlin UINT ? Or any workarounds known?

[SteinerOk]

Hey, @ZacSweers, do you have any plans or updates here?