Support older versions of Kotlin

[amr]

Hi, my project is running on Kotlin 1.4 and I wish I could make use of this project. Do you think it's possible to be backwards compatible with older versions of Kotlin?

I could work on a PR if the idea is accepted.

[nsk90]

Hi, have you tried to use library as is? What errors do you have?

[nsk90]

I am not sure about kotlin version, but I used to think that jvmTarget = "1.8" is responsible for backward compatibility.

[amr]

This is the error I get FYI:

Class 'ru.nsk.kstatemachine.Event' was compiled with an incompatible version of Kotlin. The binary version of its metadata is 1.6.0, expected version is 1.4.2.

I was actually able to fix the error and use the library by switching to the 1.6 compiler/stdlib, and using apiVersion = 1.4 & languageVersion = 1.4 to maintain compatibility with my project.

[amr]

Should we close this or are you interested in perhaps compiling against older versions of Kotlin?

[nsk90]

If there is a way to use language features from actual release (1.7) in a library and generate binaries that are compatible for 3 releases back (to 1.4) I think it should be done on library side. I have to play with those args that you mentioned.

[nsk90]

Please, let me know if you know correct configuration to archive this.

[amr]

I'm struggling to understand compatibility in Kotlin world. I thought the only things that matter are the JVM target and the kotlin stdlib and other JARs, but the error I got above threw me off.

I've found this article by @zsmb13 very helpful in understanding the binary compatibility aspect, which is very important for library authors. Also check this out: https://github.com/Kotlin/binary-compatibility-validator, these links don't directly address the issue here but I think they are very helpful for library authors nonetheless.

But I still can't understand why would an older kotlin compiler be bothered with class files that were compiled using a new kotlin compiler, given they all understand & compile to the same JVM bytecode version.

I'm trying to actively read on the subject and will share more once I get a better understanding.

[nsk90]

Link for original docs, for theme https://kotlinlang.org/docs/compatibility-modes.html#binary-compatibility-warnings

[nsk90]

Done in https://github.com/nsk90/kstatemachine/releases/tag/v0.11.0 , please check that everything works fine.

[amr]

@nsk90 I traveled for two weeks and just got back, during that time I also asked some relevant questions on r/kotlin and got some clarity on the situation. Please check the thread out.

I checked the tag and it all looks good. You may choose to continue on 1.4, but I should also say that being on 1.6/1.7 can totally work too. The only thing it changes is which minimum kotlin compiler version others would need to use, but it doesn't affect their freedom to use the Kotlin API & Language version they need.