gradle-errorprone-plugin

This plugin configures JavaCompile tasks to use Error Prone.

Requirements

This plugin requires using at least Gradle 6.8.

While JDK 8 is supported, it is recommended to use at least a JDK 9 compiler. See note below about JDK 8 support.

There's no specific support for the Android Gradle Plugin. Read on to better understand what you need to do to use both plugins together. Specifically, note that source sets below are only about standard Gradle source sets for JVM projects, not Android source sets, so anything done by the plugin based on source sets won't be done at all for Android projects.

Usage

plugins {
    id("net.ltgt.errorprone") version "<plugin version>"
}

This plugin creates a configuration named errorprone, and configures the <sourceSet>AnnotationProcessor configuration for each source set to extend it. This allows configuring Error Prone dependencies from a single place.

Error Prone needs to be added as a dependency in this configuration:

repositories {
    mavenCentral()
}
dependencies {
    errorprone("com.google.errorprone:error_prone_core:$errorproneVersion")
}

[!CAUTION] Using a dynamic or changing version for Error Prone, such as latest.release or 2.+, means that your build could fail at any time, if a new version of Error Prone adds or enables new checks that your code would trigger.

Error Prone can then be configured on the JavaCompile tasks:

import net.ltgt.gradle.errorprone.errorprone

tasks.withType<JavaCompile>().configureEach {
    options.errorprone.disableWarningsInGeneratedCode.set(true)
}

and can also be disabled altogether:

tasks {
    compileTestJava {
        options.errorprone.isEnabled.set(false)
    }
}

Note that this plugin only enables Error Prone on tasks for source sets (i.e. compileJava for the main source set, compileTestJava for the test source set, and compileIntegTestJava for a custom integTest source set).

JDK 8 support

Error Prone requires at least a JDK 9 compiler. When using a JDK 8 compiler, the plugin will configure the JavaCompile tasks to use a forking compiler and will override the compiler by prepending the Error Prone javac to the bootstrap classpath (using a -Xbootclasspath/p: JVM argument).

You can configure JavaCompile tasks to use a specific JDK compiler, independently of the JDK used to run Gradle itself. The plugin will use the toolchain version, if any is specified, to configure the task. This allows you to enforce compilation with JDK 11 while running Gradle with JDK 8. (In case you would want to enforce compilation with JDK 8 instead, the plugin would detect it and properly configure the bootstrap classpath as described above)

Note that the plugin will ignore any task that forks and defines either a javaHome or an executable, and thus won't configure the bootstrap classpath if you're e.g. running Gradle with a more recent JDK and forking the compilation tasks to use JDK 8.

JDK 16+ support

Starting with JDK 16, due to JEP 396: Strongly Encapsulate JDK Internals by Default, --add-opens and --add-exports arguments need to be passed to the compiler's JVM.

The plugin will automatically use a forking compiler and pass the necessary JVM arguments whenever it detects such a JDK is being used and ErrorProne is enabled (unless the Gradle daemon's JVM already was given the appropriate options through org.gradle.jvmargs).

That detection will only take into account the toolchain used by the JavaCompile task, or the JDK used to run Gradle in case no toolchain is being used. The plugin will ignore any task that forks and defines either a javaHome or an executable, and thus won't configure the JVM arguments if you're e.g. running Gradle with an older JDK and forking the compilation tasks to use JDK 17.

Note that the plugin also configures the JVM arguments for any JDK above version 9 to silence related warnings, but they will then only be used if the task is explicitly configured for forking (or if the configured toolchain is incompatible with the JDK used to run Gradle, which will then implicitly fork a compiler daemon).

Android Gradle Plugin support

As noted above, this plugin won't have much effect when used in conjunction with the AGP rather than, say, Gradle's built-in Java plugins.

It will then:

• create the errorprone configuration, but won't wire it to any other configuration, and by extension to any compilation task
• enhance JavaCompile tasks with the errorprone extension, but keep ErrorProne disabled by default (it would fail otherwise, as ErrorProne won't be on the processor path)

You'll thus have to somehow:

• put ErrorProne on the processor path of the JavaCompile tasks
• enable ErrorProne on the JavaCompile tasks
• configure isCompilingTestOnlyCode for compilation tasks for test variants (this changes the behavior of some checks)

This could (and should) be done by a plugin, so if you have deep knowledge of the AGP APIs and how to idiomatically integrate Error Prone within Android builds, please make such a plugin and I'll link to it here for others to use.

Custom Error Prone checks

Custom Error Prone checks can be added to the errorprone configuration too:

dependencies {
    errorprone("com.uber.nullaway:nullaway:$nullawayVersion")
}

or alternatively to the <sourceSet>AnnotationProcessor configuration, if they only need to be enabled for a given source set:

dependencies {
    annotationProcessor("com.google.guava:guava-beta-checker:$betaCheckerVersion")
}

and can then be configured on the tasks; for example:

tasks.withType<JavaCompile>().configureEach {
    options.errorprone {
        option("NullAway:AnnotatedPackages", "net.ltgt")
    }
}
tasks.compileJava {
    // The check defaults to a warning, bump it up to an error for the main sources
    options.errorprone.error("NullAway")
}

[!NOTE] These examples use NullAway. Note that I made a companion plugin specifically to surface NullAway options as Gradle DSL properties.

Configuration

As noted above, this plugin adds an errorprone extension to the JavaCompile.options. It can be configured either as a property (options.errorprone.xxx) or script block (options.errorprone { … }).

In a *.gradle.kts script, the Kotlin extensions need to be imported:

import net.ltgt.gradle.errorprone.errorprone

Properties

_Please note that all properties are lazy._

Methods

A check severity can take values: DEFAULT, OFF, WARN, or ERROR.
Note that the net.ltgt.gradle.errorprone.CheckSeverity needs to be imported into your build scripts (see examples above).