For Developers

Getting started

We use the Maven build system. We are using version 3. Download Maven

Error Prone requires JDK 17 or higher to build. Additionally, you must have certain JDK versions configured in your ~/.m2/toolchains.xml to successfully build Error Prone and run tests. At a minimum, it should have toolchain entries for JDK 17, JDK 25 ea (available from here), and whatever JDK version you use to run Maven. Here is an example toolchains.xml file you can edit and use, which works if you are running Maven on JDK 21:

<?xml version="1.0" encoding="UTF-8"?>
<toolchains xmlns="http://maven.apache.org/TOOLCHAINS/1.1.0"
            xsi:schemaLocation="http://maven.apache.org/TOOLCHAINS/1.1.0 http://maven.apache.org/xsd/toolchains-1.1.0.xsd"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <toolchain>
        <type>jdk</type>
        <provides>
            <version>21</version>
        </provides>
        <configuration>
            <jdkHome>/path/to/jdk21</jdkHome>
        </configuration>
    </toolchain>
    <toolchain>
        <type>jdk</type>
        <provides>
            <version>25</version>
        </provides>
        <configuration>
            <jdkHome>/path/to/jdk25</jdkHome>
        </configuration>
    </toolchain>
    <toolchain>
        <type>jdk</type>
        <provides>
            <version>17</version>
        </provides>
        <configuration>
            <jdkHome>/path/to/jdk17</jdkHome>
        </configuration>
    </toolchain>
</toolchains>

The required JDK versions may change over time; check out which versions are installed in the CI configuration to get the latest information.

Build the library:

$ cd error-prone
$ mvn package

You'll also need to configure your IDE to build with a supported JDK.

A Maven plugin for your IDE should setup the project very conveniently, and a git plugin can simplify source code management. The core developers use IntelliJ IDEA or Eclipse.

It's very useful and recommended to locate the sources for your JDK and attach them in the IDE, so you can navigate into the javac libraries when needed.

We generally follow the Sun style guide, and limit lines to 100 cols.

Write a checker

Let's say you want to write a checker and contribute it to the project. Here are the steps you should follow.

Set up your work environment

Follow the Getting Started steps above. Then create a branch in which to do your work.

You should also add the check to the Issue Tracker (if it is not already there), comment that you are taking the issue over, and change the status from "New" to "Accepted".

IDE Configuration

Eclipse

We recommend installing the m2e-apt plugin and enabling preferences > maven > annotation processing so AutoValue is run automatically.

Intellij

We provide an intellij code style that conforms to Google Java Style: https://github.com/google/error-prone/blob/master/.idea/GoogleStyle.xml

To install it, copy GoogleStyle.xml to your intellij configuration directory (e.g. ~/.IntelliJIdea14/config/codestyles/ for intellij 14 on linux, or ~/Library/Preferences/IdeaIC14/codestyles/ for intellij 14 on mac). Then select 'Google Style' in Settings > Editor > Code Style.

Write your checker

Checkers are in the package com.google.errorprone.bugpatterns. You can follow the tutorial on writing a check here. Don't forget to write tests!

Request a code review

A member of error-prone team needs to review your code and merge it into the mainline project. We use github for code reviews.