# The Groovy Plugin

version 9.8.0-milestone-2

The Groovy plugin extends the Java plugin to add support for Groovy projects. It can deal with Groovy code, mixed Groovy and Java code, and even pure Java code (although we don’t necessarily recommend to use it for the latter). The plugin supports joint compilation, which allows you to freely mix and match Groovy and Java code, with dependencies in both directions. For example, a Groovy class can extend a Java class that in turn extends a Groovy class. This makes it possible to use the best language for the job, and to rewrite any class in the other language if needed.

Note that if you want to benefit from the API / implementation separation, you can also apply the `java-library` plugin to your Groovy project.

## Usage

To use the Groovy plugin, include the following in your build script:

build.gradle.kts

    plugins {
        groovy
    }

build.gradle

    plugins {
        id 'groovy'
    }

## Tasks

The Groovy plugin adds the following tasks to the project. Information about altering the dependencies to Java compile tasks is found here.

`compileGroovy` — GroovyCompile

  Depends on: `compileJava`

  Compiles production Groovy source files.

`compileTestGroovy` — GroovyCompile

  Depends on: `compileTestJava`

  Compiles test Groovy source files.

`compileSourceSetGroovy` — GroovyCompile

  Depends on: `compileSourceSetJava`

  Compiles the given source set’s Groovy source files.

`groovydoc` — Groovydoc

  Generates API documentation for the production Groovy source files.

The Groovy plugin adds the following dependencies to tasks added by the Java plugin.

Table 1. Groovy plugin - additional task dependencies
Task name | Depends on
--- | ---
`classes` | `compileGroovy`
`testClasses` | `compileTestGroovy`
`sourceSetClasses` | `compileSourceSetGroovy`

Figure 1. Groovy plugin - tasks

## Project layout

The Groovy plugin assumes the project layout shown in Groovy Layout. All the Groovy source directories can contain Groovy and Java code. The Java source directories may only contain Java source code.[1] None of these directories need to exist or have anything in them; the Groovy plugin will simply compile whatever it finds.

`src/main/java`

  Production Java source.

`src/main/resources`

  Production resources, such as XML and properties files.

`src/main/groovy`

  Production Groovy source. May also contain Java source files for joint compilation.

`src/test/java`

  Test Java source.

`src/test/resources`

  Test resources.

`src/test/groovy`

  Test Groovy source. May also contain Java source files for joint compilation.

`src/sourceSet/java`

  Java source for the source set named sourceSet.

`src/sourceSet/resources`

  Resources for the source set named sourceSet.

`src/sourceSet/groovy`

  Groovy source files for the given source set. May also contain Java source files for joint compilation.

### Changing the project layout

Just like the Java plugin, the Groovy plugin allows you to configure custom locations for Groovy production and test source files.

build.gradle.kts

    sourceSets {
        main {
            groovy {
                setSrcDirs(listOf("src/groovy"))
            }
        }

        test {
            groovy {
                setSrcDirs(listOf("test/groovy"))
            }
        }
    }

build.gradle

    sourceSets {
        main {
            groovy {
                srcDirs = ['src/groovy']
            }
        }

        test {
            groovy {
                srcDirs = ['test/groovy']
            }
        }
    }

## Dependency management

Because Gradle’s build language is based on Groovy, Gradle already ships with a Groovy library. Nevertheless, Groovy projects need to explicitly declare a Groovy dependency. This dependency will then be used on compile and runtime class paths. It will also be used to get hold of the Groovy compiler and Groovydoc tool, respectively.

If Groovy is used for production code, the Groovy dependency should be added to the `implementation` configuration:

build.gradle.kts

    dependencies {
        implementation("org.codehaus.groovy:groovy-all:2.4.15")
    }

build.gradle

    dependencies {
        implementation 'org.codehaus.groovy:groovy-all:2.4.15'
    }

If Groovy is only used for test code, the Groovy dependency should be added to the `testImplementation` configuration:

build.gradle.kts

    dependencies {
        testImplementation("org.codehaus.groovy:groovy-all:2.4.15")
    }

build.gradle

    dependencies {
        testImplementation 'org.codehaus.groovy:groovy-all:2.4.15'
    }

To use the Groovy library that ships with Gradle, declare a `localGroovy()` dependency. Note that different Gradle versions ship with different Groovy versions; as such, using `localGroovy()` is less safe than declaring a regular Groovy dependency.

build.gradle.kts

    dependencies {
        implementation(localGroovy())
    }

build.gradle

    dependencies {
        implementation localGroovy()
    }

## Automatic configuration of groovyClasspath

The `GroovyCompile` and `Groovydoc` tasks consume Groovy code in two ways: on their `classpath`, and on their `groovyClasspath`. The former is used to locate classes referenced by the source code, and will typically contain the Groovy library along with other libraries. The latter is used to load and execute the Groovy compiler and Groovydoc tool, respectively, and should only contain the Groovy library and its dependencies.

Unless a task’s `groovyClasspath` is configured explicitly, the Groovy (base) plugin will try to infer it from the task’s `classpath`. This is done as follows:

- If a `groovy-all(-indy)` Jar is found on `classpath`, that jar will be added to `groovyClasspath`.

- If a `groovy(-indy)` jar is found on `classpath`, and the project has at least one repository declared, a corresponding `groovy(-indy)` repository dependency will be added to `groovyClasspath`.

- Otherwise, execution of the task will fail with a message saying that `groovyClasspath` could not be inferred.

Note that the “-indy” variation of each jar refers to the version with `invokedynamic` support.

## Convention properties

The Groovy plugin does not add any convention properties to the project.

## Source set properties

The Groovy plugin adds the following extensions to each source set in the project. You can use these properties in your build script as though they were properties of the source set object.

### Groovy Plugin — source set properties

`groovy` — GroovySourceDirectorySet (read-only)

  Default value: Not null

  The Groovy source files of this source set. Contains all `.groovy` and `.java` files found in the Groovy source directories, and excludes all other types of files.

`groovy.srcDirs` — `Set<File>`

  Default value: `[projectDir/src/name/groovy]`

  The source directories containing the Groovy source files of this source set. May also contain Java source files for joint compilation. Can set using anything described in Specifying Multiple Files.

The Groovy plugin also modifies some source set properties:

### Groovy Plugin - modified source set properties

Property name | Change
--- | ---
`allJava` | Adds all `.java` files found in the Groovy source directories.
`allSource` | Adds all source files found in the Groovy source directories.

## GroovyCompile

The Groovy plugin adds a GroovyCompile task for each source set in the project. The task type shares much with the `JavaCompile` task by extending `AbstractCompile` (see the relevant Java Plugin section). The `GroovyCompile` task supports most configuration options of the official Groovy compiler. The task can also leverage the Java toolchain support.

Table 2. Groovy plugin - GroovyCompile properties
Task Property | Type | Default Value
--- | --- | ---
`classpath` | FileCollection | `sourceSet.compileClasspath`
`source` | FileTree. Can set using anything described in Specifying Multiple Files. | `sourceSet.groovy`
`destinationDirectory` | `File`. | `sourceSet.groovy.destinationDirectory`
`groovyClasspath` | FileCollection | `groovy` configuration if non-empty; Groovy library found on `classpath` otherwise
`javaLauncher` | `Property<JavaLauncher>`, see the toolchain documentation. | None but will be configured if a toolchain is defined on the `java` extension.

### Compilation avoidance

Caveat: Groovy compilation avoidance is an incubating feature since Gradle 5.6. There are known inaccuracies so please enable it at your own risk.

To enable the incubating support for Groovy compilation avoidance, add a `enableFeaturePreview` to your settings file:

settings.gradle.kts

    enableFeaturePreview("GROOVY_COMPILATION_AVOIDANCE")

settings.gradle

    enableFeaturePreview('GROOVY_COMPILATION_AVOIDANCE')

If a dependent project has changed in an ABI-compatible way (only its private API has changed), then Groovy compilation tasks will be up-to-date. This means that if project `A` depends on project `B` and a class in `B` is changed in an ABI-compatible way (typically, changing only the body of a method), then Gradle won’t recompile `A`.

See Java compile avoidance for a detailed list of the types of changes that do not affect the ABI and are ignored.

However, similar to Java’s annotation processing, there are various ways to customize the Groovy compilation process, for which implementation details matter. Some well-known examples are Groovy AST transformations. In these cases, these dependencies must be declared separately in a classpath called `astTransformationClasspath`:

build.gradle.kts

    val astTransformation = configurations.create("astTransformation")
    dependencies {
        astTransformation(project(":ast-transformation"))
    }
    tasks.withType<GroovyCompile>().configureEach {
        astTransformationClasspath.from(astTransformation)
    }

build.gradle

    configurations { astTransformation }
    dependencies {
        astTransformation(project(":ast-transformation"))
    }
    tasks.withType(GroovyCompile).configureEach {
        astTransformationClasspath.from(configurations.astTransformation)
    }

## Incremental Groovy compilation

Since Gradle 5.6, Gradle has included an experimental incremental Groovy compiler. To enable incremental compilation for Groovy, you need:

- Enable Groovy compilation avoidance.

- Explicitly enable incremental Groovy compilation in the build script:

buildSrc/src/main/kotlin/myproject.groovy-conventions.gradle.kts

    tasks.withType<GroovyCompile>().configureEach {
        options.isIncremental = true
        options.incrementalAfterFailure = true
    }

buildSrc/src/main/groovy/myproject.groovy-conventions.gradle

    tasks.withType(GroovyCompile).configureEach {
        options.incremental = true
        options.incrementalAfterFailure = true
    }

This gives you the following benefits:

- Incremental builds are much faster.

- If only a small set of Groovy source files are changed, only the affected source files will be recompiled. Classes that don’t need to be recompiled remain unchanged in the output directory. For example, if you only change a few Groovy test classes, you don’t need to recompile all Groovy test source files — only the changed ones need to be recompiled.

To understand how incremental compilation works, see Incremental Java compilation for a detailed overview. Note that there are several differences from Java incremental compilation:

The Groovy compiler doesn’t keep `@Retention` in generated annotation class bytecode (GROOVY-9185), thus all annotations are `RUNTIME`. This means that changes to source-retention annotations won’t trigger a full recompilation.

### Known issues

Also see Known issues for incremental Java compilation.

- Changes to resources won’t trigger a recompilation, this might result in some incorrectness — for example Extension Modules.

## Compiling and testing for Java 6 or Java 7

With toolchain support added to `GroovyCompile`, it is possible to compile Groovy code using a different Java version than the one running Gradle. If you also have Java source files, this will also configure `JavaCompile` to use the right Java compiler, as can be seen in the Java plugin documentation.

### Example: Configure Java 7 build for Groovy

build.gradle.kts

    java {
        toolchain {
            languageVersion = JavaLanguageVersion.of(7)
        }
    }

build.gradle

    java {
        toolchain {
            languageVersion = JavaLanguageVersion.of(7)
        }
    }

1. Gradle uses the same conventions as introduced by Russel Winder’s Gant tool.