What is AST Inspector? How to use the PHP AST step debugger?

This article will introduce to you what AST Inspector is and how to use the PHP AST step debugger. I hope it will be helpful to friends in need~

When you learn to write custom rules for PHPStan or Rector, you also Must learn more about PHP programming language.

More precisely, it's about the way the interpreter parses PHP code. The result of parsing PHP code is a node tree that represents the structure of the code. For example, you will have a definition node for a class, a definition node for a method, and declaration nodes within these methods, etc.

Each node can be checked for errors (using PHPStan), or automatically reconstructed in some way (using Rector). [Recommended learning: PHP video tutorial]

This node tree is called Abstract Syntax Tree. A successful PHPStan or Rector rule must first be selected from the tree correct nodes and "subscribe" your rules to these nodes. A common approach is to start var_dump-ing or echo-ing the node in your new rule, but I find this to be tedious.

That's why I created a simple command line tool that lets you inspect the nodes of any given PHP file.

This tool is called AST Inspector and can be found on GitHub.

GitHub address: https://github.com/matthiasnoback/php-ast-inspector/

Install it with Composer.

composer require --dev matthiasnoback/php-ast-inspector

Then run.

vendor/bin/ast-inspect inspect [file.php]

You will see something similar to this output.

You can navigate in the tree by going to the next or previous node, or jump to the child nodes of the selected node. Navigation can be easily done using the a,s,d,w keys.

Currently this project uses the PHP-Parser library for parsing. Since PHPStan adds extra virtual nodes to the AST, it would also be useful to display them in this tool, but it requires some extra work. Another interesting addition is to display the types deduced by PHPStan for variables in the code being inspected. This also requires some extra work...

Now, give this program a try.

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