Using Rector for Safe Code Modernization

Rector automatically rewrites PHP source with configured upgrade or quality rules. Its changes must be reviewed just like human-written code.

What It Does

Install Rector in the project rather than a global, unpinned tool. Limit transformations to explicitly chosen paths and Rector rule sets.

Requirements and Compatibility

Use a supported PHP runtime and install any third-party tool or extension explicitly shown in the examples. Commands should be run from the project root unless stated otherwise.

Syntax, Inputs and Results

The examples separate configuration, the smallest working operation and a realistic follow-up task. Adapt file paths and dependency versions to your own project.

Example 1: Basic Use

Install Rector in the project rather than a global, unpinned tool.

composer require --dev rector/rector
vendor/bin/rector --version

Example 2: Another Case

Limit transformations to explicitly chosen paths and Rector rule sets.

<?php
// File: rector.php
use Rector\Config\RectorConfig;
return RectorConfig::configure()
    ->withPaths([__DIR__ . '/src'])
    ->withPreparedSets(deadCode: true, codeQuality: true);

Practical Example

Preview, test and then apply the same configured changes.

vendor/bin/rector process --dry-run
vendor/bin/phpunit
vendor/bin/rector process

For production, apply the compatibility and edge-case limits described below.

Important Behavior and Edge Cases

Run Rector in dry-run mode first, inspect the diff, run tests, and avoid applying broad rule sets blindly.

Comparison with Related Functions and Tools

Subject	Key difference
Direct function calls vs injectable services	Constructor injection exposes collaborators so they can be replaced during testing.

Common Beginner Mistakes

Mistake	Correct approach
Relying on a demonstration as production validation	Add explicit error handling and test all inputs that can change behavior.
Skipping the prerequisite of this specific workflow	Install or configure the named tool and confirm the example can actually run.
Ignoring edge conditions	Run Rector in dry-run mode first, inspect the diff, run tests, and avoid applying broad rule sets blindly.

Key Takeaways

Rector automatically rewrites PHP source with configured upgrade or quality rules. Its changes must be reviewed just like human-written code.
Run Rector in dry-run mode first, inspect the diff, run tests, and avoid applying broad rule sets blindly.
Keep application configuration, source code and validation tests under version control.

Use these examples as a starting point, then validate the result with the actual PHP build, dependencies and inputs used by your application.