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. Turn 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

When the eclipse plugin is applied, the eclipse task will auto-configure the generated files to enable annotation processing in Eclipse.

When using Buildship, you'll have to manually run the eclipseJdtApt and eclipseFactorypath tasks to generate the Eclipse configuration files, then manually enable annotation processing: in the project properties → Java Compiler → Annotation Processing, check Enable Annotation Processing.

In any case, the eclipse plugin has to be applied to the project.

IntelliJ IDEA

When the idea plugin is applied, the idea task will auto-configure the generated files to enable annotation processing in intelliJ IDEA.

When using the Gradle integration in IntelliJ IDEA however, rather than the idea task, 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. 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, you'll have to uncheck Create separate module per source set when importing the project.

In any case, the idea plugin has to be applied to the project.

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

johnny / gradle-apt-plugin