Add back PayPal as the default payment method in the installer

core/lib/generators/solidus/install/app_templates/payment_method/paypal.rb

@@ -0,0 +1,9 @@
+unless Bundler.locked_gems.dependencies['solidus_frontend']
+  say_status :warning, "Support for frontends other than `solidus_frontend` by `solidus_paypal_commerce_platform` is still in progress.", :yellow
+end
+
+unless Bundler.locked_gems.dependencies['solidus_paypal_commerce_platform']
+  bundle_command 'add solidus_paypal_commerce_platform'
+end
+
+generate 'solidus_paypal_commerce_platform:install'

core/lib/generators/solidus/install/install_generator.rb

@@ -29,6 +29,7 @@ class InstallGenerator < Rails::Generators::AppBase
     ]
 
     PAYMENT_METHODS = %w[
+      paypal
       none
     ]
 
@@ -317,13 +318,17 @@ def detect_authentication_to_install
     end
 
     def detect_payment_method_to_install
+      return 'paypal' if Bundler.locked_gems.dependencies['solidus_paypal_commerce_platform']
       options[:payment_method] ||
+        (options[:auto_accept] && @selected_frontend == 'classic' ? 'paypal' : 'none') ||
+        (@selected_frontend != 'classic' && 'none') || # bail out if it's not classic
         ask_with_description(
-          default: 'none',
+          default: 'paypal',
           limited_to: PAYMENT_METHODS,
           desc: <<~TEXT
             Which payment method would you like to use?
 
+            - [#{set_color 'paypal', :bold}] Install `solidus_paypal_commerce_platform` (#{set_color :default, :bold}).
             - [#{set_color 'none', :bold}] Skip installing a payment method.
           TEXT
         )

core/spec/generators/solidus/install/install_generator_spec.rb

@@ -19,6 +19,17 @@
       end
     end
 
+    it 'defaults to "paypal" for payments when frontend is "classic"' do
+      generator = described_class.new([], ['--auto-accept', '--frontend=classic'])
+      generator.prepare_options
+
+      aggregate_failures do
+        expect(generator.instance_variable_get(:@selected_frontend)).to eq("classic")
+        expect(generator.instance_variable_get(:@selected_authentication)).to eq("devise")
+        expect(generator.instance_variable_get(:@selected_payment_method)).to eq("paypal")
+      end
+    end
+
     it 'disables "seeds" and "sample" if "migrate" are disabled' do
       generator = described_class.new([], ['--auto-accept', '--migrate=false'])
       generator.prepare_options