EnvironmentInterface seems to be a useless type to expect / depend on

[Rarst]

Slim\Container declares default environment service to be an implementation of EnvironmentInterface.

Slim\App expects a container that implements Psr\Container\ContainerInterface
with these service keys configured and ready for use:

 - environment: an instance of \Slim\Interfaces\Http\EnvironmentInterface

@property-read \Slim\Interfaces\Http\EnvironmentInterface environment

Thing is EnvironmentInterface doesn’t contain anything actually needed for it to work, only test–related mock().

This means that this $app->getContainer()->environment->get('foo'); won’t be understood by any tools, because the interface doesn’t have get().

Also the classes that depend on environment like Slim\Http\Request::createFromEnvironment(Environment $environment) all require specific Slim\Environment class, not the interface. So trying to replace environment service with something that implements EnvironmentInterface would break the app.

It feels like either:

1. EnvironmentInterface should be expanded to comprehensively describe a generic replaceable service, in analogue to ContainerInterface. Other components of the app should be changed to depend on the interface, not the implementation.
2. Inline documentation should reflect the de–facto dependency on concrete Environment implementation, not the interface.

[Rarst]

Hey, I noticed this was tagged as a workable issue... But I could use some feedback on which approach is desirable here?

[jdrieghe]

I made a small PR that implements one of your proposals: #2625.
If it's decided to go with this, I'm more than willing to do the same for the documentation.