Clone the CitizensAPI and Citizens2 repositories. Citizens2 uses Maven subprojects for backwards compatibility with old Minecraft versions.
Citizens welcomes open source contributions. Make sure you sign the CLA when making a pull request.
Make sure you have installed all prerequisite Spigot versions using java BuildTools.jar --rev <1.12.2|1.13.2|1.14.4|1.15.2...>
.
Build the Citizens JAR by running maven install
in the main directory; the output JAR will be located at dist/target/Citizens-xxx.jar
.