Hi guys, how to mark a closure or lambda as

@Input

, I tried something like:

kt
  @get:Optional
  @get:Input
  public open val keyTransformer: Property<KeyTransformer> = objectFactory.property()

  public fun interface KeyTransformer : Serializable {
    public fun transform(key: String): String
  }

but it fails for:

java.lang.NoClassDefFoundError: com/github/jengelman/gradle/plugins/shadow/transformers/KeyTransformer
  at org.gradle.internal.cc.impl.serialize.ClassLoadingKt.classForName(ClassLoading.kt:27)
  at org.gradle.internal.cc.impl.serialize.DefaultClassDecoder.decodeClass(DefaultClassDecoder.kt:50)
  at org.gradle.internal.serialize.graph.DefaultReadContext.readClass(Contexts.kt:288)
  at org.gradle.internal.serialize.graph.codecs.BeanCodec.decode(BeanCodec.kt:41)
  at org.gradle.internal.serialize.graph.CombinatorsKt$reentrant$1$decodeLoop$1.invokeSuspend(Combinators.kt:122)
  at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
  at kotlin.coroutines.ContinuationKt.startCoroutine(Continuation.kt:115)

or

> Cannot fingerprint input property 'transformers.PropertiesFileTransformer_Decorated$0.keyTransformer': value 'build_6c52heuashhvkr1mlhojx3t85$1@30280cc3' cannot be serialized.

You can‘t really capture a function as input. Inputs should be data, such as scalar values or files. What’s the bigger picture here? Do you want to let users specify the behavior of the task?

I wan't to make ShadowJar task re-executed after keyTransformer changed, keyTransformer is configurable, but seems no way to do so. https://github.com/GradleUp/shadow/blob/main/src/main/kotlin/com/github/jengelman/[…]gradle/plugins/shadow/transformers/PropertiesFileTransformer.kt

I think you'd have to create another

@Input

property and expose the dynamic value as a ValueSource

That sounds like a good idea!

You could look into Gradle‘s code how Copy tracks the closures passed to from and into. But I don‘t think it does it correctly. I think if you have an up to date Copy and you change the closure it‘s still up to date 🤷‍♂️

@get:Nested val keyTransformer: Property<(String) -> String>

might work

I think this is in fact an open issue in the Copy tasks: https://github.com/gradle/gradle/issues/861 (known issue for 8 years 🙈 ) Generally, I think there it is solved by all closures/lambdas/actions filling a CopySpec, which is then serializable. But having that ability to define a

(String)->String

transformer as input would be interesting for a couple of use cases. I had a similar request for a plugin recently... Please share if you discover a working solution.

Thanks for your sharing.