Historically, Gradle has shipped with some Groovy types in very prominent APIs.
This required the Kotlin DSL to add special integration to work with Groovy closures.
This has also forced plugins written in languages other than Groovy to use Groovy types for some APIs.

When the Kotlin DSL was introduced, we made an effort to add non-Groovy equivalents for all APIs.
This has been mostly done, but there remain a few hold outs (fixing these are out of scope).

Historically, Gradle has shipped with some Groovy types in very prominent APIs.
This required the Kotlin DSL to add special integration to work with Groovy closures.
This has also forced plugins written in languages other than Groovy to use Groovy types for some APIs.

When the Kotlin DSL was introduced, we made an effort to add non-Groovy equivalents for all APIs.
This has been mostly done, but there remain a few holdouts (fixing these is out of scope).