fix(Address): Set name from firstname and lastname on update

If use_combined_first_and_last_name_in_address is false (default) and firstname and lastname are given in the changeset (ie. from a form)
we need to make sure that name is set from it, otherwise
data will be inconsistent.

Closes #4094

core/app/models/spree/address.rb

@@ -84,6 +84,7 @@ def self.immutable_merge(existing_address, new_attributes)
     # @return [Hash] hash of attributes contributing to value equality with optional merge
     def self.value_attributes(base_attributes, merge_attributes = {})
       base = base_attributes.stringify_keys.merge(merge_attributes.stringify_keys)
+      base.delete("name") unless Spree::Config.use_combined_first_and_last_name_in_address
 
       name_from_attributes = Spree::Address::Name.from_attributes(base)
       if base['firstname'].presence || base['first_name'].presence

core/spec/models/spree/address_spec.rb

@@ -109,7 +109,7 @@
     end
   end
 
-  context "when saving a record" do
+  context "when creating a record" do
     context "when the `name` field is not explicitly set" do
       subject { build :address, name: nil, firstname: 'John', lastname: 'Doe' }
 
@@ -119,6 +119,50 @@
     end
   end
 
+  context "when updating a record" do
+    let(:address) { create(:address, firstname: "John", lastname: "Doe") }
+
+    context "if use_combined_first_and_last_name_in_address is set to false (default)" do
+      before do
+        allow(Spree::Config).to receive(:use_combined_first_and_last_name_in_address) { false }
+      end
+
+      context "and the `name` attribute is not in changeset" do
+        it "sets `name` from `firstname` and `lastname`" do
+          new_address = described_class.immutable_merge(address, firstname: "Jane", lastname: "Fonda")
+          expect(new_address.read_attribute(:name)).to eq("Jane Fonda")
+        end
+      end
+
+      context "and the `name` attribute is in changeset" do
+        it "does not update name" do
+          new_address = described_class.immutable_merge(address, name: "Jane Fonda")
+          expect(new_address.read_attribute(:name)).to eq("John Von Doe")
+        end
+      end
+    end
+
+    context "if use_combined_first_and_last_name_in_address is set to true" do
+      before do
+        allow(Spree::Config).to receive(:use_combined_first_and_last_name_in_address) { true }
+      end
+
+      context "and the `name` attribute is not in changeset" do
+        it "keeps old name" do
+          new_address = described_class.immutable_merge(address, firstname: "Jane", lastname: "Fonda")
+          expect(new_address.read_attribute(:name)).to eq("John Von Doe")
+        end
+      end
+
+      context "and the `name` attribute is in changeset" do
+        it "updates name" do
+          new_address = described_class.immutable_merge(address, name: "Jane Fonda")
+          expect(new_address.read_attribute(:name)).to eq("Jane Fonda")
+        end
+      end
+    end
+  end
+
   context ".build_default" do
     context "no user given" do
       let!(:default_country) { create(:country) }