Registering multiple transforms with the same values of attributes should fail

[hungvietnguyen]

Current Behavior

Open the attached project: TransformWithSameAttributes.zip

It has the following transform setup (expand to see)

import org.gradle.api.artifacts.type.ArtifactTypeDefinition.ARTIFACT_TYPE_ATTRIBUTE

plugins {
    java
}

dependencies {
    implementation("com.google.guava:listenablefuture:1.0")
}

abstract class ExampleTransform : TransformAction<ExampleTransform.Parameters> {

    interface Parameters : TransformParameters {
        @get:Input
        var minSdkVersion: Int
    }

    @get:InputArtifact
    abstract val inputArtifact: Provider<FileSystemLocation>

    override
    fun transform(outputs: TransformOutputs) {
        println("Running transform with minSdk = ${parameters.minSdkVersion} for artifact ${inputArtifact.get().asFile.path}")
        outputs.file("transformed-minSdk-${parameters.minSdkVersion}-${inputArtifact.get().asFile.name}").createNewFile()
    }
}

val minSdkAttribute = Attribute.of("minSdkAttribute", String::class.java)

// NOTE: We will register 2 transforms and 2 tasks for the 2 minSdk values below.
for (minSdk in listOf(21, 24)) {
    dependencies {
        registerTransform(ExampleTransform::class) {
            parameters.minSdkVersion = minSdk
            // BUG: If we forget to set the minSdkAttribute below, Gradle should fail because 2
            // transforms are registered with the same set of attributes, but currently Gradle
            // doesn't fail.
//            from.attribute(minSdkAttribute, minSdk.toString())
//            to.attribute(minSdkAttribute, minSdk.toString())
            from.attribute(ARTIFACT_TYPE_ATTRIBUTE, "jar")
            to.attribute(ARTIFACT_TYPE_ATTRIBUTE, "transformed")
        }
    }
    tasks.register("printArtifacts$minSdk") {
        val artifactFiles = configurations.getByName("runtimeClasspath").incoming.artifactView {
            attributes {
                attribute(minSdkAttribute, minSdk.toString())
                attribute(ARTIFACT_TYPE_ATTRIBUTE, "transformed")
            }
        }.artifacts.artifactFiles
        inputs.files(artifactFiles)
        doLast {
            println("Transformed artifact: ${artifactFiles.files}")
        }
    }
}

The idea is that we register 2 transforms with the same set of attributes (by accident), but Gradle doesn't fail, therefore causing latent errors that are hard to debug.

For example: Running ./gradlew --stop -Dgradle.user.home=gradle-user-home && rm -rf gradle-user-home/caches/transforms-3 && ./gradlew printArtifacts21 printArtifacts24 -Dgradle.user.home=gradle-user-home will produce the following log:

> Task :printArtifacts21
Running transform with minSdk = 24 for artifact TransformWithSameAttributes/gradle-user-home/caches/modules-2/files-2.1/com.google.guava/listenablefuture/1.0/c949a840a6acbc5268d088e47b04177bf90b3cad/listenablefuture-1.0.jar
Transformed artifact: [TransformWithSameAttributes/gradle-user-home/caches/transforms-3/12cf933ebe09a55ab0718d0a63694f35/transformed/transformed-minSdk-24-listenablefuture-1.0.jar]

> Task :printArtifacts24
Transformed artifact: [TransformWithSameAttributes/gradle-user-home/caches/transforms-3/12cf933ebe09a55ab0718d0a63694f35/transformed/transformed-minSdk-24-listenablefuture-1.0.jar]

It shows that the transform for minSdk = 21 didn't run, and the task :printArtifacts21 is supposed to get the transformed artifact with minSdk = 21 but it gets the transformed artifact with minSdk = 24 instead.

Expected Behavior

It's easy for the users to forget to set the necessary attributes. One could say it's the responsibility of the users. But Gradle could easily help users avoid that mistake by failing the build when multiple transforms are registered with the same values of attributes.

Context (optional)

This is a simplified example of a real bug that we have in the Android Gradle plugin (https://issuetracker.google.com/293206305 - "NoClassDefFoundError with AGP 8.1.0, desugaring and minify"). When setting up L8DesugarLibTransform, we forgot to set up the minSdkVersion attribute even though it is an input to the transform.

Steps to Reproduce

(See above)

Gradle version

8.4

Build scan URL (optional)

No response

Your Environment (optional)

No response

[hungvietnguyen]

Note that the new behavior will be a breaking change: It will fail the build for user projects if they use plugins / plugin versions where the transforms are not registered properly.

This belongs to the group of Gradle's validation problems, so I'm guessing there is already a process for introducing such a breaking change.

[cobexer]

Thank you for your interest in Gradle!

This feature request is in the backlog of the relevant team, but this area of Gradle is currently not in focus. It might take a while before it gets implemented.

[britter]

I ran into the same problem, see #28960 for more details.