Why is the host java version an input to

compileKotlin

? As long as I set Kotlin

jvmTarget

(and Java

options.release

?), is there any reason 2 different JDKs would produce different class files?

Probably same as with Java? If you compile against different versions, different methods can be selected and written to the class file. For example if you use

ByteBuffer#flip

which used to return

Buffer

and now returns

ByteBuffer

.

Isn't that the whole point of

--release

?

Isn't that the whole point of --release ?

Yes

I'd expect the Kotlin compiler to either set --release according to jvmTarget or allow me to configure it

If I look at issues like https://github.com/Kotlin/kotlinx.serialization/pull/2350, I'd say it does not.

Currently the recommended way to deal with different versions is JVM toolchains. https://kotl.in/gradle/jvm/toolchain The toolchains feature will properly configure Kotlin’s

jvmTarget

, Java’s

targetCompatibility

, choose the right Java stdlib, configure publishing attributes, etc. It doesn’t cause the Kotlin compiler to be executed on the old JDK, but configures the compilation to run against that JDK. Manual configuration of

jvmTarget

is kinda a low-level configuration key, similar to Java’s

--target

, not

--release

. The Kotlin compiler has the argument

-Xjdk-release

that serves the same needs as

--release

of the Java compiler, however it’s not yet stabilized

@Alexander.Likhachev my goal is to avoid toolchains. I'd like to avoid downloading a jdk11 if I have a jdk21 on my machine (or in CI)