Don't include depends_on in dockercompose if no dependencies

railties/lib/rails/generators/rails/app/app_generator.rb

@@ -607,6 +607,20 @@ def after_bundle(&block) # :doc:
       def get_builder_class
         defined?(::AppBuilder) ? ::AppBuilder : Rails::AppBuilder
       end
+
+      def devcontainer_dependencies
+        return @devcontainer_dependencies if @devcontainer_dependencies
+
+        @devcontainer_dependencies = []
+
+        @devcontainer_dependencies << "selenium" if depends_on_system_test?
+        @devcontainer_dependencies << "redis" unless options.skip_action_cable? && options.skip_active_job?
+        @devcontainer_dependencies << "postgres" if options.database == "postgresql"
+        @devcontainer_dependencies << "mysql" if options.database == "mysql"
+        @devcontainer_dependencies << "mariadb" if options.database == "trilogy"
+
+        @devcontainer_dependencies
+      end
     end
 
     # This class handles preparation of the arguments before the AppGenerator is

railties/lib/rails/generators/rails/app/templates/.devcontainer/docker-compose.yml.tt

@@ -20,21 +20,11 @@ services:
     # (Adding the "ports" property to this file will not forward from a Codespace.)
     ports:
       - 45678:45678
+<%- if !devcontainer_dependencies.empty? -%>
     depends_on:
-<%- if depends_on_system_test? -%>
-      - selenium
-<%- end -%>
-<%- unless options.skip_active_job? && options.skip_action_cable? -%>
-      - redis
-<%- end -%>
-<%- if options.database == "postgresql" -%>
-      - postgres
-<%- end -%>
-<%- if options.database == "mysql" -%>
-      - mysql
+<%- devcontainer_dependencies.each do |dependency| -%>
+      - <%= dependency %>
 <%- end -%>
-<%- if options.database == "trilogy" -%>
-      - mariadb
 <%- end -%>
 
 <%- if depends_on_system_test? -%>

railties/test/generators/app_generator_test.rb

@@ -1263,6 +1263,7 @@ def test_devcontainer
     end
     assert_file(".devcontainer/Dockerfile")
     assert_file(".devcontainer/docker-compose.yml") do |content|
+      assert_match /depends_on:/, content
       assert_match /- selenium/, content
       assert_match /selenium:/, content
       assert_match /redis:/, content
@@ -1349,6 +1350,14 @@ def test_devcontainer_no_selenium_when_skipping_system_test
     end
   end
 
+  def test_devcontainer_no_depends_on_when_no_dependencies
+    run_generator [ destination_root, "--minimal" ]
+
+    assert_file(".devcontainer/docker-compose.yml") do |content|
+      assert_no_match /depends_on:/, content
+    end
+  end
+
   private
     def assert_node_files
       assert_file ".node-version" do |content|