Using Kotlinx Serialization 1.8.0 with Kotlin 1.9.23

[nmggithub]

Hello!

I am trying to use Kotlinx Serialization on a project that uses Kotlin 1.9.23. I've noticed that the most recent version, 1.8.0, seems to have a compile dependency on Kotlin 2.1.0: https://mvnrepository.com/artifact/org.jetbrains.kotlinx/kotlinx-serialization-core-jvm/1.8.0

Does this mean that I am unable to use it on versions previous to 2.1.0? Any help, advice, or knowledge, would be much appreciated.

Thank you!

EDIT: To clarify, when trying to use it in my 1.9.23 project, I get multiple build errors as the 2.1.0 library is clashing with everything else.

[nmggithub]

OK, I think I figured out my confusion. The README.md says that:

Using Kotlin Serialization requires Kotlin compiler 1.4.0 or higher.
https://github.com/Kotlin/kotlinx.serialization/blob/v1.8.0/README.md?plain=1#L80

However, that looks like that stopped being true around v1.7.0:
b4bf182

Am I correct in believing that that line in the README.md is no longer accurate?

[sandwwraith]

The phrase in the README refers to the fact that any kotlinx.serialization version requires at least 1.4.0. More recent versions require more recent compilers, and generally, the latest releases always depend on the latest Kotlin's.
I'm not sure it is possible to formulate the phrase clearer, since e.g. kotlinx-serialization 1.5.1 depends on Kotlin 1.8.21, but will (probably) work with 1.4. Although metadata version checks would likely prevent that.

[nmggithub]

The phrase in the README refers to the fact that any kotlinx.serialization version requires at least 1.4.0. More recent versions require more recent compilers, and generally, the latest releases always depend on the latest Kotlin's. I'm not sure it is possible to formulate the phrase clearer, since e.g. kotlinx-serialization 1.5.1 depends on Kotlin 1.8.21, but will (probably) work with 1.4. Although metadata version checks would likely prevent that.

I see. It might be nice to have a compatibility table, at the very least.

Also, given what you mentioned about how more recent versions require more recent compilers, I would assume anyone stuck on older compilers just... can't use the more recent versions (and their features)? Or are there ways to make it work?

[pdvrieze]

@nmggithub What the compiler plugin does is to generate the serializer for you. This generation changes somewhat between versions, and this means more recent compilers need more recent library versions. The other way around may (probably) work but could run into issues with some binary compatibility internal (@PublishedApi or optin) interfaces used by the generated serializers. There have not been fundamental large changes, but quite possibly smaller ones (and it is not a tested solution).

[nmggithub]

@nmggithub What the compiler plugin does is to generate the serializer for you. This generation changes somewhat between versions, and this means more recent compilers need more recent library versions. The other way around may (probably) work but could run into issues with some binary compatibility internal (@PublishedApi or optin) interfaces used by the generated serializers. There have not been fundamental large changes, but quite possibly smaller ones (and it is not a tested solution).

I see. Thank you for the information. In any case, I still think a compatibility table would be much more informative than a vague "at least 1.4.0" (even if that statement is accurate).

[sandwwraith]

I would assume anyone stuck on older compilers just... can't use the more recent versions (and their features)? Or are there ways to make it work?

That is generally true for any Kotlin library, see https://kotlinlang.org/docs/kotlin-evolution-principles.html#evolving-the-binary-format:

Preferably (but we can't guarantee it), the binary format is mostly forwards compatible with the next language release, but not later ones (in the cases when new features are not used, for example, 1.9 can understand most binaries from 2.0, but not 2.1).