Suggestion for clearer dependency constraint syntax for standalone modules

[pfazzi]

Feature Request

Q	A
New Feature	yes
RFC	yes
BC Break	no

Summary

We have some modules in the codebase that are designed to be standalone, depending only on PHP core classes. A typical example is our Clock module.

Currently, we express this constraint like this:

// The Clock module should be standalone.
// It can only use PHP core classes like DateTime.
Rule::allClasses()
    ->that(new ResideInOneOfTheseNamespaces('Acme\Clock'))
    ->should(new NotHaveDependencyOutsideNamespace(
        'Acme\Clock',
        externalDependenciesToExclude: ['DateTimeImmutable', 'DateTime']
    ))
    ->because('the Clock module must be almost standalone');

We’ve found this expression a bit verbose and hard to generalize. To make the intent more clear and easier to read, I’d like to propose supporting a more concise alternative:

Rule::namespace('Acme\Clock')
    ->canDependOnlyOn('DateTimeImmutable', 'DateTime');

This alternative would improve the readability of the rule, especially when applied to multiple modules with similar constraints (e.g., pure helpers, adapters, or low-level libraries).

Thanks!