RFC for adding association between shipping method and stock locatoin

[ono]

Following up a discussion here, I wrote RFC for the requirement. Let me know if you have any questions. I am happy to discuss more. Lost My Name team is also happy to help implementing the feature too.

[BenMorganIO]

grammar: but -> except

[JDutil]

While the reasoning behind this change is sound it's still not really clear what needs to change in the Spree::Stock classes to accomplish this. Changes are going to need to occur in the Spree::Stock::Coordinator or related classes to accomplish this, but what exactly & what consequences will that have?

[alexstoick]

Hello @JDutil

Having a look at Spree::Stock::Coordinator it looks like the required changes
would not impact much of it. As @ono mentioned in the PR - the change would be
to reject any shipping_methods.

There is already a method in Spree::Stock::Estimator which is used to select the available shipping methods for a package. The function I'm referring to is https://github.com/spree/spree/blob/master/core/app/models/spree/stock/estimator.rb#L49. It feels like adding the condition for the package.stock_location to match shipping_method.stock_location is in this place.

Looking at the rest of the code - it doesn't feel like this will touch any other parts of the system. Spree will work just fine if the shipping_rates provided for the package are correct - so there will be no other change required.

Let me know what you think!

[JDutil]

@alexstoick that looks right if you want to give it a shot updating your PR.