java.net.URL is no longer a supported property type in Gradle

[ZacSweers]

Describe the bug
Dokka currently uses URL for inputs for documentation urls, but in gradle 8.3 this warning is printed

Execution optimizations have been disabled for task ':sgp-monkeypatch-agp:dokkaHtmlPartial' to ensure correctness due to the following reasons:
  - In plugin 'org.jetbrains.dokka' type 'org.jetbrains.dokka.gradle.DokkaTaskPartial' property 'unsuppressedSourceSets.$0.externalDocumentationLinks.$0.packageListUrl' has @Input annotation used on type 'java.net.URL' or a property of this type. Reason: Type 'java.net.URL' is not supported on properties annotated with @Input because Java Serialization can be inconsistent for this type. For more information, please refer to https://docs.gradle.org/8.3-rc-4/userguide/validation_problems.html#unsupported_value_type in the Gradle documentation.

[IgnatBeresnev]

Related: #2993

[ZacSweers]

@IgnatBeresnev I saw this is marked as a 2.0 thing, but would you be open to deprecating this API for something better (probably just a String) and making the existing APIs route to it?

[3flex]

It's also deprecated in Java 20, which will lead to more reports when Gradle 8.5 is released with support for running on Java 21 as projects update to latest LTS Java version.

[whyoleg]

Hey!
We were able to overcome this issue don't breaking source/binary compatibility, and so the fix will be available in an upcoming release of Dokka. Proper removal of URL usage in Gradle will be implemented in the new Gradle plugin (#3131).
For more details, look here.

Additional note: to avoid receiving deprecation warnings when running Gradle with JDK 20 please use URI("...").toURL() instead of URL("...").
Example:

sourceLink {
   remoteUrl.set(URI("https://github.com/kotlin/dokka/tree/master/src").toURL())
}

[whyoleg]

Fixed in Dokka 2.0.0 in Dokka Gradle plugin v2