Add filter feature for stock movements

We've had feedback from folks that being able to search for stock
movements related to a variant would be helpful.

backend/app/controllers/spree/admin/stock_movements_controller.rb

@@ -6,6 +6,13 @@ class StockMovementsController < ResourceController
       belongs_to 'spree/stock_location'
       before_action :parent
 
+      def index
+        params[:q] ||= {}
+
+        @search = collection.ransack(params[:q])
+        @stock_movements = @search.result.page(params[:page])
+      end
+
       private
 
       def permitted_resource_params

backend/app/views/spree/admin/stock_movements/index.html.erb

@@ -12,6 +12,35 @@
 <% end %>
 <% admin_breadcrumb(plural_resource_name(Spree::StockMovement)) %>
 
+<% content_for :table_filter_title do %>
+  <%= t('spree.filter') %>
+<% end %>
+
+<% content_for :table_filter do %>
+  <%=
+    search_form_for(
+      [:admin, @search],
+      url: admin_stock_location_stock_movements_path(
+        params[:stock_location_id]
+    )) do |f|
+  %>
+    <div class ="row">
+      <div class="field-block col-12 col-md-6 col-lg-4 col-xl-3">
+        <div class="field">
+          <%= label_tag :q_variant_sku_eq, "#{t('spree.variant')} #{t('spree.sku')}" %>
+          <%= f.text_field :variant_sku_eq, value: params[:q][:variant_sku_eq] %>
+        </div>
+      </div>
+    </div>
+
+    <div class="clearfix"></div>
+
+    <div class="actions filter-actions">
+      <%= button_tag t('spree.filter_results'), class: 'btn btn-primary' %>
+    </div>
+  <% end %>
+<% end %>
+
 <% if @stock_movements.any? %>
 <table class="index" id='listing_stock_movements'>
   <colgroup>

backend/spec/controllers/spree/admin/stock_movements_controller_spec.rb

@@ -0,0 +1,79 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+module Spree
+  module Admin
+    describe StockMovementsController, type: :controller do
+      stub_authorization!
+
+      let!(:stock_location) do
+        create(
+          :stock_location_with_items
+        )
+      end
+
+      let!(:stock_movement_1) do
+        create(
+          :stock_movement,
+          stock_item: stock_location.stock_items.first
+        )
+      end
+
+      let!(:stock_movement_2) do
+        create(
+          :stock_movement,
+          stock_item: stock_location.stock_items.last
+        )
+      end
+
+      describe '#index' do
+        subject { get :index, params: params }
+
+        context 'with no params' do
+          let(:params) { { stock_location_id: stock_location.id } }
+
+          it 'responds with a successful status code' do
+            subject
+
+            expect(response).to be_successful
+          end
+
+          it 'responds with all the stock locations stock movements' do
+            subject
+
+            expect(assigns[:stock_movements]).to contain_exactly(
+              stock_movement_1,
+              stock_movement_2
+            )
+          end
+        end
+
+        context 'with search parameters' do
+          let(:params) do
+            {
+              stock_location_id: stock_location.id,
+              q: {
+                variant_sku_eq: stock_movement_1.stock_item.variant.sku
+              }
+            }
+          end
+
+          it 'responds with a successful status code' do
+            subject
+
+            expect(response).to be_successful
+          end
+
+          it 'responds with the stock movements that match the search criteria' do
+            subject
+
+            expect(assigns[:stock_movements]).to contain_exactly(
+              stock_movement_1,
+            )
+          end
+        end
+      end
+    end
+  end
+end

core/app/models/spree/stock_movement.rb

@@ -4,6 +4,7 @@ module Spree
   class StockMovement < Spree::Base
     belongs_to :stock_item, class_name: 'Spree::StockItem', inverse_of: :stock_movements, optional: true
     belongs_to :originator, polymorphic: true, optional: true
+    has_one :variant, through: :stock_item
 
     after_create :update_stock_item_quantity
 
@@ -12,6 +13,7 @@ class StockMovement < Spree::Base
 
     scope :recent, -> { order(created_at: :desc) }
 
+    self.whitelisted_ransackable_associations = %w[variant]
     self.whitelisted_ransackable_attributes = ['quantity']
 
     def readonly?

core/spec/models/spree/stock_movement_spec.rb

@@ -11,6 +11,10 @@
     expect(subject).to respond_to(:stock_item)
   end
 
+  it 'should have a variant' do
+    expect(subject).to respond_to(:variant)
+  end
+
   it 'is readonly unless new' do
     subject.save
     expect {