How to ensure module independence with phparkitect in legacy systems?

[tomaszhanc]

Q	A
Library version	0.5.3.0
PHP version	8.4.1

Support Question

I'm new to phparkitect and would like to know the best way to configure it for my use case. I'm open to creating a PR if something should be added to the codebase 🙌.

Big Ball of Mud into Modular Monolith

I have a legacy application that's essentially a big ball of mud. Everything is coupled to everything else. I want to start adding some separation between modules. To begin, I plan to ensure there's a single point of contact, like through a Module Facade. I tried to define the below rules:

Rule 1: Shop module can only rely on its own or shared classes, and the ProductFacade.

$rules[] = Rule::allClasses()
    ->that(new ResideInOneOfTheseNamespaces('App\Shop'))
    ->should(new NotHaveDependencyOutsideNamespace('App\Shop', ['App\Product\ProductFacade', 'App\Shared\*']))
    ->because('Modules should access other modules only through their public facades');

In an ideal situation, this would be enough, but I won't have all the modules defined initially. I will add them gradually, so I also need a rule to ensure that the rest of the codebase doesn't have coupling with the extracted module besides its facade.

Rule 2: Other places should access the Shop module only through ShopFacade

$rules[] = Rule::allClasses()
    ->that(new ResideInOneOfTheseNamespaces('')) // yes, some classes are not namespaced
    ->andThat(new NotResideInTheseNamespaces('App\Shop'))
    ->should(new NotDependsOnTheseNamespaces('App\Shop'))
    // how to exclude ShopFacade?
    ->because('Other modules should only access Shop through ShopFacade');

Questions

• How can I exclude ShopFacade as a dependency in Rule 2? Should it stay in the App\Shop namespace, or should it be moved outside?
• Is there a better way to achieve my goal? I have 20+ modules in that repository, which could lead to a messy configuration. I considered creating a builder to avoid copy-pasting, but perhaps there's a more effective method in phparkitect.

[micheleorselli]

Hey there,
interesting use case, thank you for reporting that 🙇

Question 1

How can I exclude ShopFacade as a dependency in Rule 2? Should it stay in the App\Shop namespace, or should it be moved outside?

I am not sure this is possibile with the current rules. We could add the possibility to specify an exception in NotDependsOnTheseNamespaces, something like

$rules[] = Rule::allClasses()
    ->that(new ResideInOneOfTheseNamespaces('')) // yes, some classes are not namespaced
    ->andThat(new NotResideInTheseNamespaces('App\Shop'))
    ->should(new NotDependsOnTheseNamespaces('App\Shop', ['App\Shop\ShopFacade']))
    ->because('Other modules should only access Shop through ShopFacade');

the workaround for now would me moving ShopFacade outside App/Shop.

Question 2

Is there a better way to achieve my goal? I have 20+ modules in that repository, which could lead to a messy configuration. I considered creating a builder to avoid copy-pasting, but perhaps there's a more effective method in phparkitect.

the most straightforward way to specify this kind of rules is via Rule Builders, but again I am not sure what you are asking is achievable without any workaround as under the hood the rules are the same mentioned above.

Not a solution, but since the configuration is defined in php, you can split it across multiple files. It should help keeping things more manageable.

BTW Implementing some sort of exclusion in the rule NotDependsOnTheseNamespaces should not be particularly complex, I am wondering if that would be the right approach. cc @fain182 @AlessandroMinoccheri @pfazzi

[AlessandroMinoccheri]

I agree with @micheleorselli.
Adding the possibility to exclude particular namespaces or classes can be the right way, and we did it already for other expressions like for: NotHaveDependencyOutsideNamespace.

An alternative way if you don't have too many namespaces is to use the expression: DependsOnlyOnTheseNamespaces

$rules[] = Rule::allClasses()
    ->that(new ResideInOneOfTheseNamespaces(''))
    ->andThat(new NotResideInTheseNamespaces('App\Shop'))
    ->should(new DependsOnlyOnTheseNamespaces('App\Foo', 'App\Bar')) //all namespaces except for the 'App\Shop' 
    ->because('Other modules should only access to specific namespace');

This should be used as the last workaround.
The best way is to add the exclusion in the NotHaveDependencyOutsideNamespace expression

[tomaszhanc]

Thank you for the quick response. I see there is a new Exclude checks in specific namespaces #481 about adding this, so we can close this one. Right?