MDL-84204 [docs] Document Rector installation and usage

general/development/tools/rector/index.md

@@ -0,0 +1,56 @@
+---
+title: Rector
+tags:
+  - tools
+  - PHP
+---
+
+<Since version="6.0" issueNumber="MDL-84204" />
+
+[Rector](https://getrector.com/) is a tool for automating PHP code refactoring. Moodle includes a Rector configuration to apply a selected set of refactoring rules to the codebase.
+
+## Installation {/* #installation */}
+
+From the root directory of your Moodle checkout, install the Composer dependencies:
+
+```console
+composer install
+```
+
+This also installs Rector and its dependencies.
+
+## Running Rector {/* #running-rector */}
+
+Run Rector from the root directory of your Moodle checkout:
+
+```console
+composer rector
+```
+
+By default, Rector uses Moodle's `rector.php` configuration and applies changes to the codebase. Review the changes before committing them.
+
+### Passing arguments {/* #passing-arguments */}
+
+To pass arguments to Rector, separate them from the Composer command with `--`:
+
+```console
+composer rector -- [args]
+```
+
+Replace `[args]` with Rector's command-line arguments. For example, to preview changes without modifying any files:
+
+```console
+composer rector -- --dry-run
+```
+
+To limit processing to a specific directory:
+
+```console
+composer rector -- public/mod/forum
+```
+
+To see the available options:
+
+```console
+composer rector -- --help
+```