Does the `kotlin("jvm")` plugin automatically apply the `java-library` plugin? I'm sure I remember r...

# gradle

[Sam]

Does the kotlin("jvm") plugin automatically apply the java-library plugin? I'm sure I remember reading that somewhere but I can't find a reference for it. I'm trying to debug an issue where I'm getting intermittent (!) "unresolved reference" errors when pulling in another module as an api dependency 😢 (both modules are libraries, consumed by a third separate module)

[tapchicoma]

not the JavaLibraryPlugin but JavaPlugin (JavaLibraryPlugin applies JavaPlugin internally)

[Sam]

👍 thanks. In that case, I'm confused about why my build.gradle.kts file is able to add dependencies to the api configuration. I thought the api configuration was only available if the java-library plugin was added?

[Sam]

I guess what I'm really wondering is: if I'm writing a Kotlin library (for use in a multi-project build; not published), should I apply both the Kotlin plugin and the java-library plugin, or is the Kotlin plugin alone sufficient?

[tapchicoma]

Kotlin plugin alone should be sufficient

[Sam]

Okay 👍. Why is that?

[tapchicoma]

indeed only JavaLibraryPlugin plugins adds api configuration in case of Java only project. But Kotlin plugin itself, when applied, creates api* configurations

[Sam]

Thanks, that's good to know!

[Sam]

In the docs for the java-library plugin, it mentions that

A feature of the java-library plugin is that projects which consume the library only require the classes folder for compilation, instead of the full JAR.

Do you know if that's also true when building a Kotlin library? (Either with or without the java-library plugin applied)

[Sam]

Part of the reason I'm curious is because in the sample Kotlin library in the Gradle docs, they add both the Kotlin plugin and the java-library plugin. So that suggests the java-library plugin is still useful in some way.

[tapchicoma]

I can't answer why Gradle example applies java-library as well. Probably example was not updated for some time

[Sam]

Do you think that applying the java-library plugin to a Kotlin project would do anything at all? Or would it have no effect?

[Chris Lee]

A kotlin library project should apply the java-library plugin, as the artifact is a java library (JAR file containing compiled code, with Kotlin deets overlaid).

[Sam]

Thanks Chis, do you have any more info about why? What will the java-library plugin do in the case of a Kotlin project? (If it makes a difference, my use case is a multi-project build, so no published artifacts)

[Chris Lee]

A Kotlin project is really just a Java project + Kotlin source code. even without publishing artifacts to a repository, those artifacts are shared internally between projects. Having said that, the java-library plugin adds very little on top of the Java plugin - if the issue with the `api`configuration, that is provided in the java plugin. Source for Java library plugin: https://github.com/gradle/gradle/blob/5ec3f672ed600a86280be490395d70b7bc634862/sub[…]ins/src/main/java/org/gradle/api/plugins/JavaLibraryPlugin.java

[Sam]

Thanks! So am I understanding correctly that the api configuration exists whenever the java plugin is applied, but its behaviour is different if the java-library plugin is also applied?

[Chris Lee]

Correct. Additional configuration on api is performed by the Java library plugin:

public static Configuration addApiToSourceSet(SourceSet sourceSet, ConfigurationContainer configurations) {
        Configuration apiConfiguration = maybeCreateInvisibleConfig(
            configurations,
            sourceSet.getApiConfigurationName(),
            "API dependencies for " + sourceSet + ".",
            false
        );

        Configuration compileOnlyApiConfiguration = maybeCreateInvisibleConfig(
            configurations,
            sourceSet.getCompileOnlyApiConfigurationName(),
            "Compile only API dependencies for " + sourceSet + ".",
            false
        );

        Configuration apiElementsConfiguration = configurations.getByName(sourceSet.getApiElementsConfigurationName());
        apiElementsConfiguration.extendsFrom(apiConfiguration, compileOnlyApiConfiguration);

        Configuration implementationConfiguration = configurations.getByName(sourceSet.getImplementationConfigurationName());
        implementationConfiguration.extendsFrom(apiConfiguration);

        Configuration compileOnlyConfiguration = configurations.getByName(sourceSet.getCompileOnlyConfigurationName());
        compileOnlyConfiguration.extendsFrom(compileOnlyApiConfiguration);

        return apiConfiguration;
    }

[Chris Lee]

However, if your issue is intermittent it’s unlikely related to the above, as issues there would consistently fail.

[tapchicoma]

JavaPlugin doesn't add api configurations. And I am still sure you don't need to add java-library plugin when Kotlin plugin is applied.

[Chris Lee]

this call from the Java Library plugin creates the api configuration:

JvmPluginsHelper.addApiToSourceSet(sourceSet, configurations);

[andylamax]

I also do not think you need the java-library plugin. We have plenty of java libraries built with kotlin withiut the java-library plugin