Views integration: display access restrictions

This is a subissue of #1391216: Views integration for the 6.x-2.x and 7.x-1.x version.

Problem/Motivation

It should be possible to check for address access before a Views display is rendered. For example, if user A may not see any addresses of user B, he shouldn't have access to user's B address page either.

Steps to reproduce

1. Create an address based View.
2. Create a contextual filter for User ID.
3. Create a page display with a path something like user/%/addresses2.

If you would finish here, users are able to view eachothers address listings, even if they shouldn't have access. At this point you have two options:

1. Set display access restrictions by role or permission. The downside of this is that users may not be able to view their own address listing.
2. Add an address access filter, to remove addresses from the Views results that the user may not see. The downside of this is that it doesn't work with pager and that the users still have access to the address listing page (though it would be empty for users with limited access).

This feature is a requirement for #1433034: Redesign the address book page using Views.

Proposed resolution

Implement a views access plugin that can check for address access based on the contextual filters (arguments) of the View. For a page display with a contextual filter for User ID, the access plugin would check if the current logged in user has access to any addresses of the representing user. For a page display with a contextual filter for address ID, the access plugin would check if the current logged in user has access to the single address.

As this access plugin will only work properly for path based displays, implement also a argument validator plugin. The argument validator would do the same: it would check if the current user has access to:

• For User ID contextual filter: addresses of this user.
• For Address ID contextual filter: this address.

The argument validator plugin can not replace the access plugin, because arguments are only validated when someone tries to access the display (e.g. navigates to the page) and not when a link to the page is used in a menu.

Remaining tasks

• Implement a views access plugin.
• Implement a argument validator for checking address access based on an User ID.
• Implement a argument validator for checking address access based on an Address ID.
• Write tests.

User interface changes

New options in address based Views.

API changes

None.

I'm working on it.