Fix voucher adjustments association

Add missing, "inverse_of" and "dependent" options. Use :nullify as
for "dependent" because we would want to keep the adjustments on order
even if the voucher is deleted.

app/models/spree/adjustment.rb

@@ -44,6 +44,8 @@ module Spree
 
     belongs_to :tax_rate, -> { where spree_adjustments: { originator_type: 'Spree::TaxRate' } },
                foreign_key: 'originator_id'
+    belongs_to :voucher, -> { where spree_adjustments: { originator_type: 'Spree::Voucher' } },
+               foreign_key: 'originator_id', inverse_of: :adjustments
 
     validates :label, presence: true
     validates :amount, numericality: true

app/models/voucher.rb

@@ -7,7 +7,8 @@ class Voucher < ApplicationRecord
 
   belongs_to :enterprise
 
-  has_many :adjustments, as: :originator, class_name: 'Spree::Adjustment'
+  has_many :adjustments, as: :originator, class_name: 'Spree::Adjustment', inverse_of: :voucher,
+           dependent: :nullify
 
   validates :code, presence: true, uniqueness: { scope: :enterprise_id }
 
@@ -91,6 +92,8 @@ class Voucher < ApplicationRecord
   # override the one from CalculatedAdjustments
   # Create an "open" adjustment which will be updated later once tax and other fees have
   # been applied to the order
+  #
+  # rubocop:disable Style/OptionalBooleanParameter
   def create_adjustment(label, order, mandatory = false, _state = "open", tax_category = nil)
     amount = compute_amount(order)
 
@@ -106,11 +109,13 @@ class Voucher < ApplicationRecord
 
     order.adjustments.create(adjustment_attributes)
   end
+  # rubocop:enable Style/OptionalBooleanParameter
 
   # override the one from CalculatedAdjustments so we limit adjustment to the maximum amount
   # needed to cover the order, ie if the voucher covers more than the order.total we only need
   # to create an adjustment covering the order.total
   # Doesn't work with taxes for now
+  # TODO move this to a calculator
   def compute_amount(order)
     amount = calculator.compute(order)
 

spec/models/spree/adjustment_spec.rb

@@ -18,6 +18,7 @@ module Spree
       it { is_expected.to belong_to(:order) }
       it { is_expected.to belong_to(:tax_category) }
       it { is_expected.to belong_to(:tax_rate) }
+      it { is_expected.to belong_to(:voucher) }
     end
 
     describe "scopes" do