title: Guard Usage outline: deep

Using the Guard

The mago guard command is your entry point for running all architectural validation checks.

Running the Guard

To check your entire project against the rules defined in your mago.toml file, simply run:

mago guard

Mago will scan your codebase and report any violations it finds.

Analyzing Specific Paths

You can also run the guard on specific files or directories by passing them as arguments. This is useful for focusing on a particular module or for pre-commit hooks.

# Analyze only the src/Domain directory
mago guard src/Domain

# Analyze a specific file
mago guard src/UI/Controller/UserController.php

Understanding the Output

The guard produces two types of error reports: Boundary Breaches (from the Perimeter Guard) and Structural Flaws (from the Structural Guard).

Example: Boundary Breach

If a part of your code violates a dependency rule, you'll get a "Boundary Breach" error.

Consider this rule in mago.toml:

[[guard.perimeter.rules]]
namespace = "App\\Domain\\"
permit = ["[@self](https://github.com/self)", "[@native](https://github.com/native)"]

This rule states that the App\Domain namespace can only depend on itself and native PHP symbols.

Now, if you have the following code:

// src/Domain/Model/User.php
namespace App\Domain\Model;

use App\Infrastructure\Doctrine\Orm\Entity; // <-- Violation!

class User extends Entity {}

Running mago guard would produce an error like this:

error[disallowed-use]: Illegal dependency on `App\Infrastructure\Doctrine\Orm\Entity`
  ┌─ src/Domain/Model/User.php:4:5
  │
4 │ use App\Infrastructure\Doctrine\Orm\Entity;
  │     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This `use` statement is not allowed by the architectural rules
  │
  = Breach occurred in namespace `App\Domain\Model`.
  = Dependency forbidden by architectural rules
  = The following rule(s) were evaluated but none permitted this dependency: `App\Domain\\`.
  = Help: Update your guard configuration to allow this dependency or refactor the code to remove it.

The error clearly shows the forbidden dependency, where it occurred, and which rule was violated.

Example: Structural Flaw

If a symbol doesn't adhere to a structural rule, you'll get a "Structural Flaw" error.

Consider this rule:

[[guard.structural.rules]]
on            = "App\\UI\\**\\Controller\\**"
target        = "class"
must-be-final = true
reason        = "Controllers should be final to prevent extension."

And this code:

// src/UI/Controller/UserController.php
namespace App\UI\Controller;

class UserController // <-- Violation! Not final.
{
    // ...
}

Running mago guard would report:

error[must-be-final]: Structural flaw in `App\UI\Controller\UserController`
   ┌─ src/UI/Controller/UserController.php:3:7
   │
 3 │ class UserController
   │       ^^^^^^^^^^^^^^ This must be declared as `final`
   │
   = Controllers should be final to prevent extension.
   = Help: Declare this class as `final`.
```The report identifies the symbol, the location, the exact flaw, and the reason provided in the configuration.