# Gradle Plugin Development Plugin

version 9.0.0

The Java Gradle Plugin development plugin can be used to assist in the development of Gradle plugins. It automatically applies the Java Library (`java-library`) plugin, adds the `gradleApi()` dependency to the `api` configuration and performs validation of plugin metadata during `jar` task execution.

The plugin also integrates with TestKit, a library that aids in writing and executing functional tests for plugin code. It automatically adds the `gradleTestKit()` dependency to the `testImplementation` configuration and generates a plugin classpath manifest file consumed by a `GradleRunner` instance if found. Please refer to Automatic classpath injection with the Plugin Development Plugin for more on its usage, configuration options and samples.

## Usage

To use the Java Gradle Plugin Development plugin, include the following in your build script:

Example 1. Using the Java Gradle Plugin Development plugin
build.gradle.kts

    plugins {
        `java-gradle-plugin`
    }

build.gradle

    plugins {
        id 'java-gradle-plugin'
    }

Applying the plugin automatically applies the Java Library(`java-library`) plugin and adds the `gradleApi()` dependency to the `api` configuration. It also adds some validations to the build.

The following validations are performed:

- There is a plugin descriptor defined for the plugin.

- The plugin descriptor contains an `implementation-class` property.

- The `implementation-class` property references a valid class file in the jar.

- Each property getter or the corresponding field must be annotated with a property annotation like `@InputFile` and `@OutputDirectory`. Properties that don’t participate in up-to-date checks should be annotated with `@Internal`.

Any failed validations will result in a warning message.

For each plugin you are developing, add an entry to the `gradlePlugin {}` script block:

Example 2. Using the gradlePlugin {} block.
build.gradle.kts

    gradlePlugin {
        plugins {
            create("simplePlugin") {
                id = "org.gradle.sample.simple-plugin"
                implementationClass = "org.gradle.sample.SimplePlugin"
            }
        }
    }

build.gradle

    gradlePlugin {
        plugins {
            simplePlugin {
                id = 'org.gradle.sample.simple-plugin'
                implementationClass = 'org.gradle.sample.SimplePlugin'
            }
        }
    }

The `gradlePlugin {}` block defines the plugins being built by the project including the `id` and `implementationClass` of the plugin. From this data about the plugins being developed, Gradle can automatically:

- Generate the plugin descriptor in the `jar` file’s `META-INF` directory.

- Configure the Plugin Marker Artifact publications (Maven or Ivy) for each plugin.

- Publish each plugin to the Gradle Plugin Portal (see Publishing Plugins to Gradle Plugin Portal for details), but only if the Plugin Publishing Plugin has also been applied.

## Interactions

Some of the plugin’s behaviour depends on other, related plugins also being applied in your build, namely the Maven Publish (`maven-publish`) and Ivy Publish (`ivy-publish`) plugins.

Other plugins auto apply the Java Gradle Plugin, like the Plugin Publishing Plugin.

### Maven Publish Plugin

When the Java Gradle Plugin (`java-gradle-plugin`) detects that the Maven Publish Plugin (`maven-publish`) is also applied by the build, it will automatically configure the following MavenPublications:

- a single "main" publication, named `pluginMaven`, based on the main Java component

- multiple "marker" publications (one for each plugin defined in the `gradlePlugin {}` block), named `<pluginName>PluginMarkerMaven` (for example in the above example it would be `simplePluginPluginMarkerMaven`)

This automatic configuration happens in a Project.afterEvaluate() block (so at the end of the build configuration phase), and only if these publications haven’t already been defined, so it’s possible to create and customise them during the earlier stages of build configuration.

### Ivy Publish Plugin

When the Java Gradle Plugin(`java-gradle-plugin`) detects that the Ivy Publish Plugin (`ivy-publish`) is also applied by the build, it will automatically configure the following IvyPublications:

- a single "main" publication, named `pluginIvy`, based on the main Java component

- multiple "marker" publications (one for each plugin defined in the `gradlePlugin {}` block), named `<pluginName>PluginMarkerIvy` (for example in the above example it would be `simplePluginPluginMarkerIvy`)

This automatic configuration happens in a Project.afterEvaluate() block (so at the end of the build configuration phase), and only if these publications haven’t already been defined, so it’s possible to create and customise them during the earlier stages of build configuration.

### Plugin Publish Plugin

Starting from version 1.0.0, the Plugin Publish Plugin always auto-applies the Java Gradle Plugin (`java-gradle-plugin`) and the Maven Publish Plugin (`maven-publish`).