Neo4j 3.0 introduced user-defined procedures, while Neo4j 3.1 added user-defined functions, and Neo4j 3.2 will support custom aggregate functions, enabling direct extension of Cypher. These additions allow for easier interaction with other data stores, enhanced import/export functionalities, and implementation of graph algorithms. The Neo4j Procedure Compiler helps write safer code by detecting common errors before deployment, and it has been integrated into Neo4j 3.1.0. The compiler checks for various rule violations, such as proper parameter annotations, return types, and field access methods, providing detailed error feedback for invalid procedures or functions. Enabling the compiler is straightforward, requiring only adding it to the classpath, and it can be used with Maven or Gradle dependencies.