Is it a requirement to specify module dependencies in both module-info.java and build.gradle.kts

Question

This is my multi-project Gradle setup:

.
└── gradle-module-project
    ├── application
    ├── build.gradle.kts
    ├── gradlew
    ├── list
    ├── settings.gradle.kts
    └── utilities

application, utilties and list are projects, and inside each one there is a Java Module.

That is, each project has its own src/main/java/module-info.java file and build.gradle.kts file.

application module depends on utilities module, and utilities module depends on list module.

build.gradle.kts at the root contains the following:

subprojects {
    ..

    plugins.withType<JavaPlugin>().configureEach {
        configure<JavaPluginExtension> {
            modularity.inferModulePath.set(true)
        }
    }
    
    ..
}

What I find strange is that inside each sub-project, the build.gradle.kts is required to list the dependencies.

For example, application -> build.gradle.kts contains:

plugins {
    application
}

dependencies {
    implementation(project(":utilities"))
}

..

Why does build.gradle.kts for application have to include implementation(project(":utilities"))?

When the module-info.java inside application already specifies what that module depends on.

Doesn't this seem like duplication?

Is it intended that the dependency must be specified in both module-info.java and build.gradle.kts?

Answer 1

When using Java Modules with Gradle, dependencies have to be specified twice: once for the benefit of the module system and again for the benefit of the build tool.

I've been following along with the Easy Text demo application in Java 9 Modularity by Sandor Mak and Paul Bakker, which is a multi-module project. The module-info.java for one module is:

module easytext.cli {
   requires easytext.analysis;
}

When I wrap it in Gradle, in my build.gradle file I also need:

dependencies {
    implementation project(':easytext.analysis')
}

Perhaps it's just a matter of time before the tooling catches up and we won't have to do both.

Also check out Paul Bakker's JavaOne presentation Building JPMS Modules with Java in which he goes through the fine-detail of building multiple-module Java/Groovy/Kotlin projects with Gradle.