Don’t configure Kamal storage volume if not needed

Configuring a persistent storage volume in Kamal
is needed only for sqlite or Active Storage. If
using a different database or the
--skip-active-storage option, this configuration
can be skipped.

railties/lib/rails/generators/app_base.rb

@@ -366,6 +366,10 @@ module Rails
         options[:skip_active_storage]
       end
 
+      def skip_storage? # :doc:
+        skip_active_storage? && !sqlite3?
+      end
+
       def skip_action_cable? # :doc:
         options[:skip_action_cable]
       end
@@ -784,7 +788,7 @@ module Rails
       def dockerfile_chown_directories
         directories = %w(log tmp)
 
-        directories << "storage" unless skip_active_storage? && !sqlite3?
+        directories << "storage" unless skip_storage?
         directories << "db" unless skip_active_record?
 
         directories.sort

railties/lib/rails/generators/rails/app/templates/config/deploy.yml.tt

@@ -31,11 +31,13 @@ env:
   # clear:
   #   DB_HOST: 192.168.0.2
 
+<% unless skip_storage? %>
 # Use a persistent storage volume for sqlite database files and local Active Storage files.
 # Recommended to change this to a mounted volume path that is backed up off server.
 volumes:
   - "<%= app_name %>_storage:/rails/storage"
 
+<% end %>
 # Bridge fingerprinted assets, like JS and CSS, between versions to avoid
 # hitting 404 on in-flight requests. Combines all files from new and old
 # version inside the asset_path.

railties/test/generators/app_generator_test.rb

@@ -668,6 +668,34 @@ class AppGeneratorTest < Rails::Generators::TestCase
     assert_no_file ".env.erb"
   end
 
+  def test_inclusion_of_kamal_storage_volume
+    run_generator_and_bundler [destination_root]
+
+    assert_file "config/deploy.yml" do |content|
+      assert_match(%r{storage:/rails/storage}, content)
+    end
+  end
+
+  def test_inclusion_of_kamal_storage_volume_if_only_skip_active_storage_is_given
+    run_generator_and_bundler [destination_root, "--skip-active-storage"]
+
+    assert_file "config/deploy.yml" do |content|
+      assert_match(%r{storage:/rails/storage}, content)
+    end
+  end
+
+  def test_kamal_storage_volume_is_skipped_if_required
+    run_generator_and_bundler [
+      destination_root,
+      "--skip-active-storage",
+      "--database=postgresql"
+    ]
+
+    assert_file "config/deploy.yml" do |content|
+      assert_no_match(%r{storage:/rails/storage}, content)
+    end
+  end
+
   def test_usage_read_from_file
     assert_called(File, :read, returns: "USAGE FROM FILE") do
       assert_equal "USAGE FROM FILE", Rails::Generators::AppGenerator.desc