Awesome

gradle-apt-plugin

The goal of this plugin was to eventually no longer be needed, being superseded by built-in features. This has become a reality with Gradle 5.2 and IntelliJ IDEA 2019.1. tl;dr: this plugin is obsolete, don't use it. If you're using Eclipse though, continue reading.

It originally did a few things to make it easier/safer to use Java annotation processors in a Gradle build. Those things are now available natively in Gradle, so what's this plugin about?

If you use older versions of Gradle (pre-4.6), you can still benefit from those features:

• it ensures the presence of configurations for your compile-time only dependencies (annotations, generally) and annotation processors, consistently across all supported Gradle versions;
• automatically configures the corresponding JavaCompile and GroovyCompile tasks to make use of these configurations, when the java or groovy plugin is applied.

With recent versions of Gradle (between 4.6 and 5.1), this plugin will actually only:

• add some DSL to configure annotation processors; it is however recommended to directly configure the tasks' options.compilerArgs;
• backport the sourceSet.output.generatedSourcesDirs Gradle 5.2 API;
• configure JavaCompile and GroovyCompile tasks' options.annotationProcessorGeneratedSourcesDirectory with a sane default value so you can see the generated sources in your IDE and for debugging, and avoid shipping them in your JARs.

With Gradle 5.2 and later, only the (deprecated) DSL is contributed.

Quite ironically, what you'd have probably found the most useful here was the part that was only provided as a "best effort", namely the net.ltgt.apt-idea or net.ltgt.apt-eclipse plugins that will automatically configures IntelliJ IDEA and Eclipse respectively.

If you're interested in better IDE support, please vote for those issues to eventually have built-in support:

• in Gradle for the idea and eclipse plugins
• in Eclipse Buildship
• in IntelliJ IDEA for annotation processing in the IDE (probably low priority as delegating build/run actions to Gradle is becoming the default in 2019.1) (fixed in 2019.3)

If you're using Eclipse, please migrate to the com.diffplug.eclipse.apt plugin, which is a (maintained) fork of net.ltgt.apt-eclipse.

Note: the documentation below only applies to version 0.21. For version 0.20, see the previous version of this README. For previous versions, please see this even earlier version.

Do without the plugin

This only applies if you are using Gradle ≥ 4.3

Do without net.ltgt.apt

DSL aside, the net.ltgt.apt plugin, is equivalent to the following snippet (unless otherwise noted, all snippets here assume Gradle ≥ 4.9, and only deal with Java projects, not Groovy ones):

// Workaround for https://github.com/gradle/gradle/issues/4956
sourceSets.configureEach { sourceSet ->
  tasks.named(sourceSet.compileJavaTaskName).configure {
    options.annotationProcessorGeneratedSourcesDirectory = file("$buildDir/generated/sources/annotationProcessor/java/${sourceSet.name}")
  }
}

// Workaround for https://github.com/gradle/gradle/issues/4956
sourceSets.configureEach {
    tasks.named<JavaCompile>(compileJavaTaskName) {
        options.annotationProcessorGeneratedSourcesDirectory = file("$buildDir/generated/sources/annotationProcessor/java/${this@configureEach.name}")
    }
}

With Gradle ≤ 4.6, you'll also need to create the <sourceSet>AnnotationProcessor configurations and configure the tasks' options.annotationProcessorPath (the following snippet will disable falling back to the compilation classpath to resolve annotation processors though):

sourceSets.all {
  def annotationProcessorConfiguration = configurations.create(name == "main" ? "annotationProcessor" : "${name}AnnotationProcessor")
  tasks[compileJavaTaskName].options.annotationProcessorPath = annotationProcessorConfiguration
}

Alternatively, you can selectively create configurations and configure tasks as needed:

configurations {
  annotationProcessor
}
compileJava {
  options.annotationProcessorPath = configurations.annotationProcessor
}

Do without net.ltgt.apt-idea

If you're delegating IDEA build/run actions to Gradle, and/or somehow don't want or need IntelliJ IDEA to do the annotation processing, the net.ltgt.apt-idea plugin is roughly equivalent to the following snippet (this assumes a somewhat recent version of IntelliJ IDEA that automatically unexcludes source folders inside excluded folders):

// Workaround for https://youtrack.jetbrains.com/issue/IDEA-182577
idea {
  module {
    sourceDirs += compileJava.options.annotationProcessorGeneratedSourcesDirectory
    generatedSourceDirs += compileJava.options.annotationProcessorGeneratedSourcesDirectory
    testSourceDirs += compileTestJava.options.annotationProcessorGeneratedSourcesDirectory
    generatedSourceDirs += compileTestJava.options.annotationProcessorGeneratedSourcesDirectory
  }
}

// Workaround for https://youtrack.jetbrains.com/issue/IDEA-182577
idea {
    module {
        tasks.getByName<JavaCompile>("compileJava").options.annotationProcessorGeneratedSourcesDirectory?.also {
            // For some reason, modifying the existing collections doesn't work. We need to copy the values and then assign it back.
            sourceDirs = sourceDirs + it
            generatedSourceDirs = generatedSourceDirs + it
        }
        tasks.getByName<JavaCompile>("compileTestJava").options.annotationProcessorGeneratedSourcesDirectory?.also {
            // For some reason, modifying the existing collections doesn't work. We need to copy the values and then assign it back.
            testSourceDirs = testSourceDirs + it
            generatedSourceDirs = generatedSourceDirs + it
        }
    }
}

You can instead use:

// Workaround for https://youtrack.jetbrains.com/issue/IDEA-182577
idea {
  module {
    sourceDirs += sourceSets.main.output.generatedSourcesDirs
    generatedSourceDirs += sourceSets.main.output.generatedSourcesDirs
    testSourceDirs += sourceSets.test.output.generatedSourcesDirs
    generatedSourceDirs += sourceSets.test.output.generatedSourcesDirs
  }
}

// Workaround for https://youtrack.jetbrains.com/issue/IDEA-182577
idea {
    module {
        tasks.sourceSets.getByName(SourceSet.MAIN_SOURCE_SET_NAME).output.generatedSourcesDirs.also {
            // For some reason, modifying the existing collections doesn't work. We need to copy the values and then assign it back.
            sourceDirs = sourceDirs + it
            generatedSourceDirs = generatedSourceDirs + it
        }
        tasks.sourceSets.getByName(SourceSet.TEST_SOURCE_SET_NAME).output.generatedSourcesDirs.also {
            // For some reason, modifying the existing collections doesn't work. We need to copy the values and then assign it back.
            testSourceDirs = testSourceDirs + it
            generatedSourceDirs = generatedSourceDirs + it
        }
    }
}

If you want IntelliJ IDEA to process annotations, you'll have to do some manual configuration to enable annotation processing, and add the annotation processors to the project's compilation classpath:

// Workaround for https://youtrack.jetbrains.com/issue/IDEA-187868
idea {
  module {
    scopes.PROVIDED.plus += configurations.annotationProcessor
    scopes.TEST.plus += configurations.testAnnotationProcessor
  }
}

// Workaround for https://youtrack.jetbrains.com/issue/IDEA-187868
idea {
    module {
        scopes["PROVIDED"]!!["plus"]!!.add(configurations.annotationProcessor)
        scopes["TEST"]!!["plus"]!!.add(configurations.testAnnotationProcessor)
    }
}

If you want to apply this configuration automatically for every project, you can do this with an init script similar to the following:

import org.gradle.util.GradleVersion;

// If running from IntelliJ IDEA (such as when importing the project)
if (Boolean.getBoolean("idea.active")) {
  def HAS_PROCESSOR_GENERATED_SOURCES_DIR = GradleVersion.current() >= GradleVersion.version("4.3")

  allprojects { project ->
    project.apply plugin: 'idea'

    if (HAS_PROCESSOR_GENERATED_SOURCES_DIR) {
      project.plugins.withType(JavaPlugin) {
        project.afterEvaluate {
          project.idea.module {
            def mainGeneratedSources = project.tasks["compileJava"].options.annotationProcessorGeneratedSourcesDirectory
            if (mainGeneratedSources) {
              sourceDirs += mainGeneratedSources
              generatedSourceDirs += mainGeneratedSources
            }
            def testGeneratedSources = project.tasks["compileTestJava"].options.annotationProcessorGeneratedSourcesDirectory
            if (testGeneratedSources) {
              testSourceDirs += testGeneratedSources
              generatedSourceDirs += testGeneratedSources
            }

            // Uncomment if you want to do annotation processing in IntelliJ IDEA:
            // def annotationProcessorConfiguration = configurations.findByName("annotationProcessor")
            // if (annotationProcessorConfiguration) {
            //   scopes.PROVIDED.plus += annotationProcessorConfiguration
            // }
            // def testAnnotationProcessorConfiguration = configurations.findByName("testAnnotationProcessor")
            // if (testAnnotationProcessorConfiguration) {
            //   scopes.TEST.plus += testAnnotationProcessorConfiguration
            // }
          }
        }
      }
    } else {
      // fallback to automatically applying net.ltgt.apt-idea whenever net.ltgt.apt is used
      project.plugins.withId("net.ltgt.apt") {
        try {
          project.apply plugin: "net.ltgt.apt-idea"
          // Comment if you want to do annotation processing in IntelliJ IDEA:
          project.plugins.withType(JavaPlugin) {
            project.afterEvaluate {
              project.idea.module.apt.addAptDependencies = false
            }
          }
        } catch (UnknownPluginException) {
          // ignore, in case an older version of net.ltgt.apt is being used
          // that doesn't come with net.ltgt.apt-idea.
        }
      }
    }
  }
}

Do without net.ltgt.apt-eclipse

There's no easy workaround at this point, sorry :man_shrugging:

Using the plugin

The plugin is published to the Plugin Portal; see instructions there: https://plugins.gradle.org/plugin/net.ltgt.apt

You will need Gradle ≥ 4.3 to use it.

Configurations

For each SourceSet, a <sourceSet>AnnotationProcessor configuration is available (Gradle ≥ 4.6 already provides those configurations)

As a result, the following configurations are available for any Java project:

• annotationProcessor
• testAnnotationProcessor

Note that those configurations don't extend each others: testAnnotationProcessor doesn't extend annotationProcessor; those configurations are only use for their respective JavaCompile and GroovyCompile tasks.

Example usage

After applying the plugin following the above instructions, those added configurations can be used when declaring dependencies:

dependencies {
  compile("com.google.dagger:dagger:2.18")
  annotationProcessor("com.google.dagger:dagger-compiler:2.18")

  // auto-factory contains both annotations and their processor, neither is needed at runtime
  compileOnly("com.google.auto.factory:auto-factory:1.0-beta6")
  annotationProcessor("com.google.auto.factory:auto-factory:1.0-beta6")

  compileOnly("org.immutables:value-annotations:2.7.1")
  annotationProcessor("org.immutables:value:2.7.1")
}

Groovy support

The plugin also configures GroovyCompile tasks added when the groovy plugin is applied. It does not however configure annotation processing for Groovy sources, only for Java sources used in joint compilation. To process annotations on Groovy sources, you'll have to configure your GroovyCompile tasks; e.g.

compileGroovy {
  groovyOptions.javaAnnotationProcessing = true
}

tasks.named<GroovyCompile>("compileGroovy") {
  groovyOptions.isJavaAnnotationProcessing = true
}

Build cache

Compilation tasks are still cacheable with the caveat that only one language can be used per source set (i.e. either src/main/java or src/main/groovy but not both), unless Groovy joint compilation is used (putting Java files in src/main/groovy), or tasks are configured to use distinct generated sources destination directories.

Gradle Kotlin DSL

The plugin provides Kotlin extensions to make configuration easier when using the Gradle Kotlin DSL. The easiest is to import net.ltgt.gradle.apt.* at the top of your *.gradle.kts file. Most APIs are the same as in Groovy, see below for differences.

Usage with IDEs

IDE configuration is provided on a best-effort basis.

Eclipse

Applying the net.ltgt.apt-eclipse plugin will auto-configure the generated files to enable annotation processing in Eclipse.

Eclipse annotation processing can be configured through a DSL, as an extension to the Eclipse JDT DSL (presented here with the default values):

eclipse {
  jdt {
    apt {
      // whether annotation processing is enabled in Eclipse
      aptEnabled = compileJava.aptOptions.annotationProcessing
      // where Eclipse will output the generated sources; values are interpreted as per project.file()
      genSrcDir = file('.apt_generated')
      genTestSrcDir = file('.apt_generated_tests')
      // whether annotation processing is enabled in the editor
      reconcileEnabled = true
      // a map of annotation processor options; a null value will pass the argument as -Akey rather than -Akey=value
      processorOptions = compileJava.aptOptions.processorArgs

      file {
        whenMerged { jdtApt ->
          // you can tinker with the JdtApt here
        }

        withProperties { properties ->
          // you can tinker with the Properties here
        }
      }
    }
  }

  factorypath {
    plusConfigurations = [ configurations.annotationProcessor, configurations.testAnnotationProcessor ]
    minusConfigurations = []

    file {
      whenMerged { factorypath ->
        // you can tinker with the Factorypath here
      }

      withXml { node ->
        // you can tinker with the Node here
      }
    }
  }
}

eclipse {
  jdt {
    apt {
      // whether annotation processing is enabled in Eclipse
      isAptEnabled = tasks.getByName<JavaCompile>("compileJava").aptOptions.annotationProcessing
      // where Eclipse will output the generated sources; values are interpreted as per project.file()
      genSrcDir = file(".apt_generated")
      genTestSrcDir = file(".apt_generated_tests")
      // whether annotation processing is enabled in the editor
      isReconcileEnabled = true
      // a map of annotation processor options; a null value will pass the argument as -Akey rather than -Akey=value
      processorOptions = tasks.getByName<JavaCompile>("compileJava").aptOptions.processorArgs

      file {
        whenMerged {
          // you can tinker with the JdtApt here, you'll need to cast 'this' to JdtApt
        }

        withProperties {
          // you can tinker with the Properties here
        }
      }
    }
  }

  factorypath {
    plusConfigurations = [ configurations.annotationProcessor, configurations.testAnnotationProcessor ]
    minusConfigurations = []

    file {
      whenMerged {
        // you can tinker with the Factorypath here, you'll need to cast 'this' to Factorypath
      }

      withXml {
        // you can tinker with the Node here
      }
    }
  }
}

When using Buildship, you'll have to manually run the eclipseJdtApt and eclipseFactorypath tasks to generate the Eclipse configuration files, then either run the eclipseJdt task or manually enable annotation processing: in the project properties → Java Compiler → Annotation Processing, check Enable Annotation Processing. Note that while all those tasks are depended on by the eclipse task, that one is incompatible with Buildship, so you have to explicitly run the two or three aforementioned tasks and not run the eclipse task.

Note that Eclipse does not distinguish main and test sources, and will process all of them using the same factory path and processor options, and the same generated source directory.

In any case, the net.ltgt.apt-eclipse plugin has to be applied to the project.

This can be configured system-wide for all projects using the net.ltgt.apt plugin by using an init script similar to the following:

allprojects { project ->
  project.plugins.withId("net.ltgt.apt") {
    // automatically apply net.ltgt.apt-eclipse whenever net.ltgt.apt is used
    try {
      project.apply plugin: "net.ltgt.apt-eclipse"
    } catch (UnknownPluginException) {
      // ignore, in case an older version of net.ltgt.apt is being used
      // that doesn't come with net.ltgt.apt-eclipse.
    }
  }
}

IntelliJ IDEA

Applying the net.ltgt.apt-idea plugin will auto-configure the generated files to enable annotation processing in IntelliJ IDEA.

When using the Gradle integration in IntelliJ IDEA (rather than the idea task), it is recommended to delegate the IDE build actions to Gradle itself starting with IDEA 2016.3: https://www.jetbrains.com/help/idea/gradle.html#delegate_build_gradle Otherwise, you'll have to manually enable annotation processing: in Settings… → Build, Execution, Deployment → Compiler → Annotation Processors, check Enable annotation processing and Obtain processors from project classpath (you'll have to make sure idea.module.apt.addAptDependencies is enabled). To mimic the Gradle behavior and generated files behavior, you can configure the production and test sources directories to build/generated/sources/annotationProcessor/java/main and build/generated/sources/annotationProcessor/java/test respectively and choose to Store generated sources relative to: Module content root.

Note that unless you delegate build actions to Gradle, you'll have to uncheck Create separate module per source set when importing the project.

IntelliJ IDEA annotation processing can be configured through a DSL, as an extension to the IDEA DSL (presented here with the default values):

idea {
  project {
    // experimental: whether annotation processing will be configured in the IDE; only actually used with the 'idea' task.
    configureAnnotationProcessing = true
  }
  module {
    apt {
      // whether generated sources dirs are added as generated sources root
      addGeneratedSourcesDirs = true
      // whether the annotationProcessor/apt and testAnnotationProcessor/testApt dependencies are added as module dependencies
      addAptDependencies = true

      // the dependency scope used for apt and/or compileOnly dependencies (when enabled above)
      mainDependenciesScope = "PROVIDED" // defaults to "COMPILE" when using the Gradle integration in IntelliJ IDEA
    }
  }
}

If you always delegate build actions to Gradle, you can thus disable idea.module.apt.addAptDependencies system-wide (there's unfortunately no way to detect this when importing the project in IDEA, so the plugin cannot configure itself automatically), by putting the following in an init script, e.g. ~/.gradle/init.d/apt-idea.gradle:

allprojects { project ->
  project.plugins.withType(JavaPlugin) {
    project.plugins.withId("net.ltgt.apt-idea") {
      project.afterEvaluate {
        project.idea.module.apt.addAptDependencies = false
      }
    }
  }
}

In any case, the net.ltgt.apt-idea plugin has to be applied to the project.

This can be configured system-wide for all projects using the net.ltgt.apt plugin by using an init script similar to the following:

allprojects { project ->
  project.plugins.withId("net.ltgt.apt") {
    try {
      // automatically apply net.ltgt.apt-idea whenever net.ltgt.apt is used
      project.apply plugin: "net.ltgt.apt-idea"
      // disable addAptDependencies (if you delegate build actions to Gradle)
      project.plugins.withType(JavaPlugin) {
        project.afterEvaluate {
          project.idea.module.apt.addAptDependencies = false
        }
      }
    } catch (UnknownPluginException) {
      // ignore, in case an older version of net.ltgt.apt is being used
      // that doesn't come with net.ltgt.apt-idea.
    }
  }
}

Configuration

The plugin makes many things configurable by enhancing source sets and tasks.

Each source set has a couple properties (Gradle ≥ 4.6 already provides those properties natively, this plugin contributes it for earlier Gradle versions):

• annotationProcessorConfigurationName (read-only String) returning the <sourceSet>AnnotationProcessor> configuration name
• annotationProcessorPath, a FileCollection defaulting to the <sourceSet>AnnotationProcessor configuration

Each source set's output gains a generatedSourcesDirs property, a FileCollection aggregating the options.annotationProcessorGeneratedSourcesDirectory for JavaCompile and GroovyCompile corresponding to the source set. This allows, for example, packaging the generated sources in a sources JAR, a dependency on output.generatedSourcesDir will automatically trigger a compilation to generate those sources. Gradle ≥ 5.2 already provides this property natively, this plugin contributes it for earlier Gradle versions.

Each JavaCompile and GroovyCompile task gains an aptOptions (read-only) property, itself with 3 properties:

• annotationProcessing, a boolean setting whether annotation processing is enabled or not; this maps to the -proc:none compiler argument, and defaults to true (meaning that argument is not passed in, and annotation processing is enabled)
• processors, a list of annotation processor class names, mapping to the -processor compiler argument
• processorArgs, a map of annotation processor options, each entry mapping to a -Akey=value compiler argument

For each source set, the corresponding JavaCompile and GroovyCompile tasks are configured such that:

• options.annotationProcessorGeneratedSourcesDirectory is set to ${project.buildDir}/generated/sources/annotationProcessor/${sourceDirectorySet.name}/${sourceSet.name}/, where $sourceirectorySet.name} will be either java or groovy (Gradle ≥ 5.2 already does that mapping natively, this plugin contributes it for earlier Gradle versions).
• options.annotationProcessorPath maps to the source set's annotationProcessorPath (Gradle ≥ 4.6 already does that mapping natively, this plugin contributes it for earlier Gradle versions)