Generate schema location urls in controller

[s-andringa]

Makes schema location URLs be generated in the controller. This way required keyword arguments for the URL helper are automatically revolved from the current path parameters. This solves an issues when Scimitar's routes are mounted inside a namespace with variable parameters. E.g. in our multitenant environment we have:

namespace :scim do
  namespace :v2 do
    resources :organizations, only: [] do
      mount Scimitar::Engine, at: '/'
      # etc...
    end
  end
end

In this case #scim_schemas_url requires the :organization_id key, which is omitted when the URL is generated in Schema::Base#as_json. This causes an error. Using the controller's URL helper fixes this.

Additionally, the controller's URL helpers can be overridden in a simple(r) manner, making Scimitar a bit more extensible. I have utilized this to test this change (see the application controller mixin for the tests).

The resource types controller already does a similar thing for resource type urls.

[s-andringa]

Unsure if generating a url here still has any value. I left it in here for backwards compatibility.

[pond]

Took a while to get my head around it and I do worry about that there's now no test coverage for any prior initialisers where the likes of #scim_schemas_url is not overridden, but that'd be tricky to figure out and perhaps not worth the effort.

The only thing holding this back from merging is an addition to README.md to let people know that this feature even exists. It looks like it'd fit in quite nicely around line 92 in the Routes section. You can see some examples of engine configuration documentation above, so a few lines to say that the routing can be overridden in a demonstrated way would be great.

Is that OK?

[s-andringa]

Is that OK?

No problem. See last commit.

Thanks for taking the time to consider and review my changes, and for maintaining this gem in general. Saved my life!

[pond]

Great stuff. Merged! Many thanks for the contribution 👍

[pond]

This is now available via RubyGems in v2.6.0 / v1.7.0.