Add RequireImportsSniff

[sirbrillig]

This sniff requires that all functions, constants, and classes be imported explicitly and marks a warning if an unimported symbol is found.

That is, you cannot just import a namespace or assume that the symbols you use are in your namespace or the global namespace, each dependency must be explicitly imported. This makes dependency trees more clear.

For example:

namespace Vehicles;
use function Vehicles\startCar;
class Car {
  public function drive() {
    startCar();
    goFaster(); // this will be a warning because `goFaster` was not imported
  }
}

Fixes #45

Questions:

• This will always add a warning for define() constants since they are never imported. Is there a way to tell the difference between a const constant and a define one? I don't think so.
• When used in WordPress this could be really annoying since it doesn't know any of the hundreds of WordPress symbols (do_action(), is_wp_error(), WP_Error, mysql2date(), etc.)
• Functions like array_map() require the fully qualified namespace, so they're likely to trigger this warning a lot.

[sirbrillig]

@stuwest I'm pleased with how this turned out, but I have a feeling that no one will want to use it, particularly for WordPress. What do you think?

[stuwest]

I agree a lot of WordPress devs won't love it, because we're so used to just winging it with globals.

This makes dependency trees more clear

But I think this is totally worth it.

This feels like a great item as a warning... but likely something that will take a lot of transitioning for existing code bases.

[sirbrillig]

One thing I think that could be problematic here is when the namespace (or part of the namespace) serves to clarify an ambiguous symbol name.

For example, if there was the function Calendar\update() (arguably we should rename the function, but that could be a tall order for existing code bases), this sniff forces it to be called as update(), requiring the developer to look at the top of the file for the context, and possibly conflicting with other names.

I'm going to discuss this further with the Neutron team, but the paths I see going forward might be:

• Use as-is, but I have a feeling it will be disabled in most places due to being too noisy.
• Allow no import if using an explicit path (this nullifies a lot of the safety-checking ability of this sniff).
• Move this sniff to its own standard so it's easier to use and control.
• Require some sort of pragma to enable this for a file (eg: a file must start with // @require-import for this sniff to do anything).

[sirbrillig]

Another issue I thought of is that functions like array_map() require the fully qualified namespace, so they're likely to trigger this warning a lot (added to the PR description). 😩

[sirbrillig]

Closing this in favor of #59 which is simpler, less noisy, and hopefully more helpful.