Bazel NullAway Example

This project demonstrates how to integrate NullAway into a Bazel Java project using Error Prone.

Overview

NullAway is a tool to help eliminate NullPointerExceptions (NPEs) in your Java code with low build-time overhead. This example shows a pattern for automatically applying NullAway to all Java targets in your project using custom Bazel rule wrappers.

Project Structure

• bazel/rules/java.bzl: Contains custom wrappers for java_library, java_binary, and java_test. These wrappers automatically add the NullAway Java plugin and the necessary javacopts to enable null checking.
• bazel/rules/BUILD.bazel: Defines the java_plugin for NullAway and Error Prone.
• src/main/java/com/example/: A sample Java application using JSpecify annotations (@Nullable).

Usage

Prerequisites

• Bazelisk (to manage the Bazel version specified in .bazelversion)
• Java JDK 25

Build

To build the project:

bazel build //...

Test

To run the tests:

bazel test //...

Demonstrating NullAway

To see NullAway in action, try modifying src/main/java/com/example/Hello.java to dereference a nullable string without a null check:

public static void main(String[] args) {
    String s = getNullableString();
    // This should trigger a NullAway error
    System.out.println(s.length()); 
}

When you run bazel build //..., the build should fail with an error from NullAway.

Configuration

NullAway is configured in bazel/rules/java.bzl with the following options:

• -Xep:NullAway:ERROR: Treats NullAway warnings as errors.
• -XepOpt:NullAway:AnnotatedPackages=com.example: Specifies which packages NullAway should analyze.
• -XDcompilePolicy=simple: Required for Error Prone plugins.

License

This project is released under the Unlicense. See LICENSE for details.