Tips for creating your first Rector rule to transform PHP code

Rector is a transformative tool for PHP code that utilizes transformation rules to modify source code, distinguishing itself from other tools like PHP CodeSniffer and PHP-Scoper by not having a predefined objective. It operates as a meta-application, capable of reproducing functionalities of existing tools by transforming code according to user-defined rules. Rector relies on two foundational libraries, PHP Parser and PHPStan, enabling it to parse and understand PHP code through Abstract Syntax Trees (AST) and conduct static code analysis. Users can define custom rules in Rector, with each rule requiring documentation, node type specification, and a refactoring logic that manipulates AST nodes. The tool supports PHP code transpiling, such as adapting newer PHP features for compatibility with older versions. The Rector repository offers a wealth of existing rules as references for creating new ones, and its codebase exemplifies programming best practices, often making use of Symfony components for various functionalities. For testing, Rector integrates with PHPUnit, offering tips for debugging and efficient test execution, and emphasizes the use of Symfony’s VarDumper for output clarity.