gradle-apt-plugin

This plugin does a few things to make it easier/safer to use Java annotation processors in a Gradle build:

it adds configurations for your compile-time only dependencies (annotations, generally) and annotation processors;
automatically configures the corresponding JavaCompile and GroovyCompile tasks to make use of these configurations, when the java or groovy plugin is applied;
automatically configures IntelliJ IDEA and/or Eclipse when the idea or eclipse plugins are applied.

Using the plugin

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

You can try snapshots using JitPack: https://jitpack.io/#tbroyer/gradle-apt-plugin

Added configurations

For each SourceSet, two configurations are added:

for Gradle < 2.12: <sourceSet>CompileOnly, extends <sourceSet>Compile (Gradle ≥ 2.12 already provides those configurations; note that this plugin doesn't provide a <sourceSet>CompileClasspath like Gradle ≥ 2.12)
<sourceSet>Apt

As a result, the following configurations are added to any Java project:

compileOnly, extends compile
apt
testCompileOnly, extends testCompile
testApt

The *Only configurations are used to specify compile-time only dependencies such as annotations that will be processed by annotation processors. Annotation processors themselves are to be added to the apt and testApt configurations.

The *Only configurations are part of the classpath of the JavaCompile and GroovyCompile tasks, whereas the apt and testApt configurations are turned into -processorpath compiler arguments. Note that up until version 0.7, if those configurations were empty, an empty processor path (-processorpath :) would be passed to javac; this was a breaking change compared to the normal behavior of Gradle, as it meant annotation processors wouldn't be looked up in the tasks' classpath. Starting with version 0.8, no -processorpath will be passed if the <sourceSet>Apt configuration is empty; this is to follow the proposal to add first-class support for annotation processing to Gradle proper

Finally, note that those configurations don't extend each others: testCompileOnly doesn't extend compileOnly, and testApt doesn't extend apt; 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:2.6"
  apt     "com.google.dagger:dagger-compiler:2.6"

  // auto-factory contains both annotations and their processor, neither is needed at runtime
  compileOnly "com.google.auto.factory:auto-factory:1.0-beta3"
  apt         "com.google.auto.factory:auto-factory:1.0-beta3"

  compileOnly "org.immutables:value:2.2.10:annotations"
  apt         "org.immutables:value:2.2.10"
}

Groovy support

Starting with version 0.6, 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
}

Usage with IDEs

IDE configuration is provided on a best-effort basis.

Eclipse

Starting with version 0.11, applying the net.ltgt.apt-eclipse plugin will auto-configure the generated files to enable annotation processing in Eclipse. In prior versions (until 0.10), that configuration would automatically happen whenever both the net.ltgt.apt and eclipse were applied (the new net.ltgt.apt-eclipse plugin will also automatically apply the net.ltgt.apt and eclipse plugins).

From version 0.11 onwards, 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; value is interpreted as per project.file()
      genSrcDir = file('.apt_generated')
      // 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.apt, configurations.testApt ]
    minusConfigurations = []

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

      withXml { node ->
        // 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 (or simply eclipse plugin up until version 0.10) 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
    project.apply plugin: "net.ltgt.apt-eclipse"
  }
}

IntelliJ IDEA

Starting with version 0.11, applying the net.ltgt.apt-idea plugin will auto-configure the generated files to enable annotation processing in IntelliJ IDEA. In prior versions (until 0.10), that configuration would automatically happen whenever both the net.ltgt.apt and idea were applied (the new net.ltgt.apt-idea plugin will also automatically apply the net.ltgt.apt and idea plugins).

When using the Gradle integration in IntelliJ IDEA (rather than the ida task), it is recommended to delegate the IDE build actions to Gradle itself starting with IDEA 2016.3: https://www.jetbrains.com/idea/whatsnew/#v2016-3-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, starting with version 0.12). To mimic the Gradle behavior and generated files behavior, you can configure the production and test sources directories to build/generated/source/apt/main and build/generated/source/apt/test respectively and choose to Store generated sources relative to: Module content root.

Note that starting with IntelliJ IDEA 2016.1, and unless you delegate build actions to Gradle, you'll have to uncheck Create separate module per source set when importing the project.

From version 0.12 onwards, 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 apt and testApt dependencies are added as module dependencies
      addAptDependencies = true

      // The following are mostly internal details; you shouldn't ever need to configure them.
      // whether the compileOnly and testCompileOnly dependencies are added as module dependencies
      addCompileOnlyDependencies = false // defaults to true in Gradle < 2.12
      // the dependency scope used for apt and/or compileOnly dependencies (when enabled above)
      mainDependenciesScope = "PROVIDED" // defaults to "COMPILE" in Gradle < 3.4, or 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 (or simply idea plugin up until version 0.10) 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-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
      }
    }
  }
}

Configuration

Starting with version 0.8, the plugin follows the proposal to add first-class support for annotation processing to Gradle proper, making many things configurable by enhancing source sets and tasks. One notable exception is that the proposed new CompileOptions properties are actually available on an aptOptions object, as the CompileOptions cannot actually be enhanced by plugins.

Each source set gains a few properties:

for Gradle < 2.12: compileOnlyConfigurationName (read-only String) returning the <sourceSet>CompileOnly configuration name; Gradle ≥ 2.12 already provides that property
aptConfigurationName (read-only String) returning the <sourceSet>Apt configuration name
processorpath, a FileCollection defaulting to the <sourceSet>Apt configuration

Each source set output gains a generatedSourcesDir property, a File defaulting to ${project.buildDir}/generated/source/apt/${sourceSet.name}.

Each JavaCompile and GroovyCompile task gains a couple properties:

generatedSourcesDestinationDir, corresponding to the -s compiler argument, i.e. whether (if set) and where to write sources files generated by annotation processors
aptOptions (read-only), itself with 4 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)
- processorpath, a FileCollection corresponding to the -processorpath compiler argument
- 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:

generatedSourcesDestinationDir maps to the source set's output.generatedSourcesDir
aptOptions.processorpath maps to the source set's processorpath

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