ktlint broken in 8.4.0 — FeatureClassLoader missing Kotlin stdlib #2894

Bug

After upgrading from 8.3.0 to 8.4.0, spotlessKotlinCheck fails for all Kotlin files. ktlint cannot initialize because Spotless' FeatureClassLoader fails to load a core Kotlin stdlib class.

Root cause from the lint output:

Caused by: java.lang.ClassNotFoundException: kotlin.collections.ArraysKt___ArraysJvmKt
    at com.diffplug.spotless.FeatureClassLoader.findClass(FeatureClassLoader.java:79)
    ...
    at com.diffplug.spotless.glue.ktlint.compat.KtLintCompat1Dot0Dot0Adapter.<clinit>(KtLintCompat1Dot0Dot0Adapter.java:68)

This happens both with ktlint("1.8.0") and ktlint() (default). Reverting to 8.3.0 fixes it.

Environment

• Spotless: 8.4.0 (8.3.0 works)
• Kotlin: 2.3.20
• Gradle: 9.4.1
• JDK: 21

Notes

The 8.4.0 changelog shows no ktlint changes. The predeclared dependencies fix might have affected how ktlint's classpath is assembled in FeatureClassLoader.