After updating Kotlin from 1.8.10 to 1.8.20 we're suddenly seeing build errors like this: > Execu...

# gradle

[xenomachina]

After updating Kotlin from 1.8.10 to 1.8.20 we're suddenly seeing build errors like this:

Execution failed for task ':jar'.

> Entry ....class is a duplicate but no duplicate handling strategy has been set. Please refer to https://docs.gradle.org/7.5.1/dsl/org.gradle.api.tasks.Copy.html#org.gradle.api.tasks.Copy:duplicatesStrategy for details.

We know we can add a duplicate strategy...

tasks.withType(Jar) {
    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
}

...but we'd like to understand why this is happening in the first place. What changed between 1.8.10 and 1.8.20 that's causing duplicate class files to be generated?

We're using Gradle 7.5.1, in case it matters.

[tapchicoma]

which Kotlin plugin are you applying?

[xenomachina]

Also 1.8.20

[tapchicoma]

which id of Kotlin plugin? Like "org.jetbrains.kotlin.jvm", "org.jetbrains.kotlin.android", etc...

[xenomachina]

We're using the legacy plugin syntax:

buildscript {
    ...
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

...

apply plugin: 'kotlin'

where $kotlin_version is set in gradle.properties.

[xenomachina]

I tried changing the apply line to:

apply plugin: "org.jetbrains.kotlin.jvm"

as documented here, and I get the same behavior: it works in 1.8.10, but complains about duplicate class files in 1.8.20.

[xenomachina]

It looks like the issue is related to the atomicfu plugin. We were applying it like this (again, legacy plugin syntax):

classpath "org.jetbrains.kotlinx:atomicfu-gradle-plugin:$atomicfu_version" // atomicfu_version = 0.20.1
...
apply plugin: 'kotlinx-atomicfu'

We are no longer using the features of this plugin, so I removed it from our build, and the duplicate class error is gone.