Generate a .devcontainer folder and its contents when creating a new app.

The .devcontainer folder includes everything needed to boot the app and do development in a remote container.

The container setup includes:
 - A redis container for Kredis, ActionCable etc.
 - A database (SQLite, Postgres, MySQL or MariaDB)
 - A Headless chrome container for system tests
 - Active Storage configured to use the local disk and with preview features working

If any of these options are skipped in the app setup they will not be included in the container configuration.

These files can be skipped using the `--no-devcontainer` option.

Co-authored-by: Rafael Mendonça França <rafael@franca.dev>

actionpack/lib/action_dispatch/system_test_case.rb

@@ -161,7 +161,7 @@ module ActionDispatch
       self.driver = SystemTesting::Driver.new(driver, **driver_options, &capabilities)
     end
 
-    # Configuration for the System Test application server
+    # Configuration for the System Test application server.
     #
     # By default this is localhost. This method allows the host and port to be specified manually.
     def self.served_by(host:, port:)

railties/CHANGELOG.md

@@ -1,3 +1,19 @@
+*   Generate a .devcontainer folder and its contents when creating a new app.
+
+    The .devcontainer folder includes everything needed to boot the app and do development in a remote container.
+
+    The container setup includes:
+     - A redis container for Kredis, ActionCable etc.
+     - A database (SQLite, Postgres, MySQL or MariaDB)
+     - A Headless chrome container for system tests
+     - Active Storage configured to use the local disk and with preview features working
+
+    If any of these options are skipped in the app setup they will not be included in the container configuration.
+
+    These files can be skipped using the `--skip-devcontainer` option.
+
+    *Andrew Novoselac & Rafael Mendonça França*
+
 *   Introduce `SystemTestCase#served_by` for configuring the System Test application server
 
     By default this is localhost. This method allows the host and port to be specified manually.

railties/lib/rails/generators.rb

@@ -23,6 +23,7 @@ module Rails
     autoload :NamedBase,       "rails/generators/named_base"
     autoload :ResourceHelpers, "rails/generators/resource_helpers"
     autoload :TestCase,        "rails/generators/test_case"
+    autoload :Devcontainer,    "rails/generators/devcontainer"
 
     mattr_accessor :namespace
 

railties/lib/rails/generators/app_base.rb

@@ -13,6 +13,7 @@ module Rails
   module Generators
     class AppBase < Base # :nodoc:
       include Database
+      include Devcontainer
       include AppName
 
       NODE_LTS_VERSION = "18.15.0"
@@ -109,6 +110,9 @@ module Rails
         class_option :skip_ci,             type: :boolean, default: nil,
                                            desc: "Skip GitHub CI files"
 
+        class_option :skip_devcontainer,   type: :boolean, default: false,
+                                           desc: "Skip devcontainer files"
+
         class_option :dev,                 type: :boolean, default: nil,
                                            desc: "Set up the #{name} with Gemfile pointing to your Rails checkout"
 
@@ -400,6 +404,10 @@ module Rails
         options[:skip_ci]
       end
 
+      def skip_devcontainer?
+        options[:skip_devcontainer]
+      end
+
       class GemfileEntry < Struct.new(:name, :version, :comment, :options, :commented_out)
         def initialize(name, version, comment, options = {}, commented_out = false)
           super

railties/lib/rails/generators/database.rb

@@ -90,6 +90,14 @@ module Rails
             "/opt/lampp/var/mysql/mysql.sock"         # xampp for linux
           ].find { |f| File.exist?(f) } unless Gem.win_platform?
         end
+
+        def mysql_database_host
+          if options[:skip_devcontainer]
+            "localhost"
+          else
+            "<%= ENV.fetch(\"DB_HOST\") { \"localhost\" } %>"
+          end
+        end
     end
   end
 end

railties/lib/rails/generators/devcontainer.rb

@@ -0,0 +1,129 @@
+# frozen_string_literal: true
+
+module Rails
+  module Generators
+    module Devcontainer
+      private
+        def devcontainer_ruby_version
+          gem_ruby_version.to_s.match(/^\d+\.\d+/).to_s
+        end
+
+        def devcontainer_dependencies
+          return @devcontainer_dependencies if @devcontainer_dependencies
+
+          @devcontainer_dependencies = []
+
+          @devcontainer_dependencies << "selenium" if depends_on_system_test?
+          @devcontainer_dependencies << "redis" if devcontainer_needs_redis?
+          @devcontainer_dependencies << db_name_for_devcontainer if db_name_for_devcontainer
+          @devcontainer_dependencies
+        end
+
+        def devcontainer_variables
+          return @devcontainer_variables if @devcontainer_variables
+
+          @devcontainer_variables = {}
+
+          @devcontainer_variables["CAPYBARA_SERVER_PORT"] = "45678" if depends_on_system_test?
+          @devcontainer_variables["SELENIUM_HOST"] = "selenium" if depends_on_system_test?
+          @devcontainer_variables["REDIS_URL"] = "redis://redis:6379/1" if devcontainer_needs_redis?
+          @devcontainer_variables["DB_HOST"] = db_name_for_devcontainer if db_name_for_devcontainer
+
+          @devcontainer_variables
+        end
+
+        def devcontainer_volumes
+          return @devcontainer_volumes if @devcontainer_volumes
+
+          @devcontainer_volumes = []
+
+          @devcontainer_volumes << "redis-data" if devcontainer_needs_redis?
+          @devcontainer_volumes << db_volume_name_for_devcontainer if db_volume_name_for_devcontainer
+
+          @devcontainer_volumes
+        end
+
+        def devcontainer_needs_redis?
+          !(options.skip_action_cable? && options.skip_active_job?)
+        end
+
+        def db_name_for_devcontainer(database = options[:database])
+          case database
+          when "mysql"          then "mysql"
+          when "trilogy"        then "mariadb"
+          when "postgresql"     then "postgres"
+          end
+        end
+
+        def db_volume_name_for_devcontainer(database = options[:database])
+          case database
+          when "mysql"          then "mysql-data"
+          when "trilogy"        then "mariadb-data"
+          when "postgresql"     then "postgres-data"
+          end
+        end
+
+        def devcontainer_db_service_yaml(**options)
+          return unless service = db_service_for_devcontainer
+
+          service.to_yaml(**options)[4..-1]
+        end
+
+        def db_service_for_devcontainer(database = options[:database])
+          case database
+          when "mysql"          then mysql_service
+          when "trilogy"        then mariadb_service
+          when "postgresql"     then postgres_service
+          end
+        end
+
+        def postgres_service
+          {
+            "postgres" => {
+              "image" => "postgres:16.1",
+              "restart" => "unless-stopped",
+              "networks" => ["default"],
+              "volumes" => ["postgres-data:/var/lib/postgresql/data"],
+              "environment" => {
+                "POSTGRES_USER" => "postgres",
+                "POSTGRES_PASSWORD" => "postgres"
+              }
+            }
+          }
+        end
+
+        def mysql_service
+          {
+            "mysql" => {
+              "image" => "mysql/mysql-server:8.0",
+              "restart" => "unless-stopped",
+              "environment" => {
+                "MYSQL_ALLOW_EMPTY_PASSWORD" => true,
+                "MYSQL_ROOT_HOST" => "%"
+              },
+              "volumes" => ["mysql-data:/var/lib/mysql"],
+              "networks" => ["default"],
+            }
+          }
+        end
+
+        def mariadb_service
+          {
+            "mariadb" => {
+              "image" => "mariadb:10.5",
+              "restart" => "unless-stopped",
+              "networks" => ["dqefault"],
+              "volumes" => ["mariadb-data:/var/lib/mysql"],
+              "environment" => {
+                "MARIADB_ALLOW_EMPTY_ROOT_PASSWORD" => true,
+              },
+            }
+          }
+        end
+
+        def db_service_names
+          ["mysql", "mariadb", "postgres"]
+        end
+    end
+  end
+end

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

@@ -266,6 +266,14 @@ module Rails
     def config_target_version
       @config_target_version || Rails::VERSION::STRING.to_f
     end
+
+    def devcontainer
+      empty_directory ".devcontainer"
+
+      template ".devcontainer/devcontainer.json"
+      template ".devcontainer/Dockerfile"
+      template ".devcontainer/compose.yaml"
+    end
   end
 
   module Generators
@@ -455,6 +463,11 @@ module Rails
         build(:storage)
       end
 
+      def create_devcontainer_files
+        return if skip_devcontainer? || options[:dummy_app]
+        build(:devcontainer)
+      end
+
       def delete_app_assets_if_api_option
         if options[:api]
           remove_dir "app/assets"

railties/lib/rails/generators/rails/app/templates/.devcontainer/Dockerfile.tt

@@ -0,0 +1,16 @@
+# Make sure RUBY_VERSION matches the Ruby version in .ruby-version
+ARG RUBY_VERSION=<%= devcontainer_ruby_version %>
+FROM mcr.microsoft.com/devcontainers/ruby:1-$RUBY_VERSION-bookworm
+
+<%- unless options.skip_active_storage -%>
+# Install packages needed to build gems
+RUN apt-get update -qq && \
+    apt-get install --no-install-recommends -y \
+      libvips \
+      #  For video thumbnails
+      ffmpeg \
+      # For pdf thumbnails. If you want to use mupdf instead of poppler,
+      # you can install the following packages instead:
+      # mupdf mupdf-tools
+      poppler-utils
+<%- end -%>

railties/lib/rails/generators/rails/app/templates/.devcontainer/compose.yaml.tt

@@ -0,0 +1,55 @@
+services:
+  rails-app:
+    build:
+      context: ..
+      dockerfile: .devcontainer/Dockerfile
+
+    volumes:
+    - ../..:/workspaces:cached
+
+    # Overrides default command so things don't shut down after the process ends.
+    command: sleep infinity
+
+    networks:
+    - default
+
+    # Uncomment the next line to use a non-root user for all processes.
+    # user: vscode
+
+    # Use "forwardPorts" in **devcontainer.json** to forward an app port locally.
+    # (Adding the "ports" property to this file will not forward from a Codespace.)
+    ports:
+    - 45678:45678
+<%- if !devcontainer_dependencies.empty? -%>
+    depends_on:
+<%- devcontainer_dependencies.each do |dependency| -%>
+    - <%= dependency %>
+<%- end -%>
+<%- end -%>
+
+<%- if depends_on_system_test? -%>
+  selenium:
+    image: seleniarm/standalone-chromium
+    restart: unless-stopped
+    networks:
+    - default
+<%- end -%>
+
+<%- if devcontainer_needs_redis? -%>
+  redis:
+    image: redis:7.2
+    restart: unless-stopped
+    networks:
+    - default
+    volumes:
+    - redis-data:/data
+<%- end -%>
+
+  <%= devcontainer_db_service_yaml(indentation: 4) %>
+
+<%- if !devcontainer_volumes.empty? -%>
+volumes:
+<%- devcontainer_volumes.each do |volume| -%>
+  <%= volume %>:
+<%- end -%>
+<%- end -%>

railties/lib/rails/generators/rails/app/templates/.devcontainer/devcontainer.json.tt

@@ -0,0 +1,34 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/ruby
+{
+  "name": "<%= app_name %>",
+  "dockerComposeFile": "compose.yaml",
+  "service": "rails-app",
+  "workspaceFolder": "/workspaces/${localWorkspaceFolderBasename}",
+
+  // Features to add to the dev container. More info: https://containers.dev/features.
+  "features": {
+    "ghcr.io/devcontainers/features/github-cli:1": {}
+  },
+
+<%- if !devcontainer_variables.empty? -%>
+  "containerEnv": {
+    <%= devcontainer_variables.map { |key, value| "\"#{key}\": \"#{value}\"" }.join(",\n    ") %>
+  },
+<%- end -%>
+
+  // Features to add to the dev container. More info: https://containers.dev/features.
+  // "features": {},
+
+  // Use 'forwardPorts' to make a list of ports inside the container available locally.
+  // "forwardPorts": [],
+
+  // Configure tool-specific properties.
+  // "customizations": {},
+
+  // Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
+  // "remoteUser": "root",
+
+  // Use 'postCreateCommand' to run commands after the container is created.
+  "postCreateCommand": "bin/setup"
+}

railties/lib/rails/generators/rails/app/templates/Dockerfile.tt

@@ -1,6 +1,6 @@
 # syntax = docker/dockerfile:1
 
-# Make sure RUBY_VERSION matches the Ruby version in .ruby-version and Gemfile
+# Make sure RUBY_VERSION matches the Ruby version in .ruby-version
 ARG RUBY_VERSION=<%= gem_ruby_version %>
 FROM registry.docker.com/library/ruby:$RUBY_VERSION-slim as base
 

railties/lib/rails/generators/rails/app/templates/config/databases/mysql.yml.tt

@@ -18,7 +18,7 @@ default: &default
 <% if mysql_socket -%>
   socket: <%= mysql_socket %>
 <% else -%>
-  host: localhost
+  host: <%= mysql_database_host %>
 <% end -%>
 
 development:

railties/lib/rails/generators/rails/app/templates/config/databases/postgresql.yml.tt

@@ -18,6 +18,13 @@ default: &default
   # For details on connection pooling, see Rails configuration guide
   # https://guides.rubyonrails.org/configuring.html#database-pooling
   pool: <%%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
+<% unless options[:skip_devcontainer] -%>
+  <%% if ENV["DB_HOST"] %>
+  host: <%%= ENV["DB_HOST"] %>
+  username: postgres
+  password: postgres
+  <%% end %>
+<% end %>
 
 development:
   <<: *default

railties/lib/rails/generators/rails/app/templates/config/databases/trilogy.yml.tt

@@ -18,7 +18,7 @@ default: &default
 <% if mysql_socket -%>
   socket: <%= mysql_socket %>
 <% else -%>
-  host: localhost
+  host: <%= mysql_database_host %>
 <% end -%>
 
 development:

railties/lib/rails/generators/rails/app/templates/test/application_system_test_case.rb.tt

@@ -1,5 +1,18 @@
 require "test_helper"
 
 class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
+<% if skip_devcontainer? -%>
+  driven_by :selenium, using: :headless_chrome, screen_size: [ 1400, 1400 ]
+<% else -%>
+  if ENV["CAPYBARA_SERVER_PORT"]
+    served_by host: "rails-app", port: ENV["CAPYBARA_SERVER_PORT"]
+
+    driven_by :selenium, using: :headless_chrome, screen_size: [ 1400, 1400 ], options: {
+      browser: :remote,
+      url: "http://#{ENV["SELENIUM_HOST"]}:4444",
+    }
+  else
     driven_by :selenium, using: :headless_chrome, screen_size: [ 1400, 1400 ]
   end
+<% end -%>
+end

railties/lib/rails/generators/rails/db/system/change/change_generator.rb

@@ -8,6 +8,7 @@ module Rails
       module System
         class ChangeGenerator < Base # :nodoc:
           include Database
+          include Devcontainer
           include AppName
 
           class_option :to, required: true,
@@ -54,6 +55,14 @@ module Rails
             end
           end
 
+          def edit_devcontainer_files
+            devcontainer_path = File.expand_path(".devcontainer", destination_root)
+            return unless File.exist?(devcontainer_path)
+
+            edit_devcontainer_json
+            edit_compose_yaml
+          end
+
           private
             def all_database_gems
               DATABASES.map { |database| gem_for_database(database) }
@@ -88,6 +97,59 @@ module Rails
               gem_name_and_version.map! { |segment| "\"#{segment}\"" }
               "gem #{gem_name_and_version.join(", ")}"
             end
+
+            def edit_devcontainer_json
+              devcontainer_json_path = File.expand_path(".devcontainer/devcontainer.json", destination_root)
+              return unless File.exist?(devcontainer_json_path)
+
+              container_env = JSON.parse(File.read(devcontainer_json_path))["containerEnv"]
+              db_name = db_name_for_devcontainer
+
+              if container_env["DB_HOST"]
+                if db_name
+                  container_env["DB_HOST"] = db_name
+                else
+                  container_env.delete("DB_HOST")
+                end
+              else
+                if db_name
+                  container_env["DB_HOST"] = db_name
+                end
+              end
+
+              new_json = JSON.pretty_generate(container_env, indent: "  ", object_nl: "\n  ")
+
+              gsub_file(".devcontainer/devcontainer.json", /("containerEnv"\s*:\s*){[^}]*}/, "\\1#{new_json}")
+            end
+
+            def edit_compose_yaml
+              compose_yaml_path = File.expand_path(".devcontainer/compose.yaml", destination_root)
+              return unless File.exist?(compose_yaml_path)
+
+              compose_config = YAML.load_file(compose_yaml_path)
+
+              db_service_names.each do |db_service_name|
+                compose_config["services"].delete(db_service_name)
+                compose_config["volumes"]&.delete("#{db_service_name}-data")
+                compose_config["services"]["rails-app"]["depends_on"]&.delete(db_service_name)
+              end
+
+              db_service = db_service_for_devcontainer
+
+              if db_service
+                compose_config["services"].merge!(db_service)
+                compose_config["volumes"] = { db_volume_name_for_devcontainer => nil }.merge(compose_config["volumes"] || {})
+                compose_config["services"]["rails-app"]["depends_on"] = [
+                  db_name_for_devcontainer,
+                  compose_config["services"]["rails-app"]["depends_on"]
+                ].flatten.compact
+              end
+
+              compose_config.delete("volumes") unless compose_config["volumes"]&.any?
+              compose_config["services"]["rails-app"].delete("depends_on") unless compose_config["services"]["rails-app"]["depends_on"]&.any?
+
+              File.write(compose_yaml_path, compose_config.to_yaml)
+            end
         end
       end
     end

railties/test/fixtures/.devcontainer/compose-minimal.yaml

@@ -0,0 +1,14 @@
+services:
+  rails-app:
+    build:
+      context: ..
+      dockerfile: .devcontainer/Dockerfile
+
+    volumes:
+    - ../..:/workspaces:cached
+
+    # Overrides default command so things don't shut down after the process ends.
+    command: sleep infinity
+
+    networks:
+    - default

railties/test/fixtures/.devcontainer/compose.yaml

@@ -0,0 +1,45 @@
+services:
+  rails-app:
+    build:
+      context: ..
+      dockerfile: .devcontainer/Dockerfile
+
+    volumes:
+      - ../..:/workspaces:cached
+
+    # Overrides default command so things don't shut down after the process ends.
+    command: sleep infinity
+
+    networks:
+    - default
+
+    # Uncomment the next line to use a non-root user for all processes.
+    # user: vscode
+
+    # Use "forwardPorts" in **devcontainer.json** to forward an app port locally.
+    # (Adding the "ports" property to this file will not forward from a Codespace.)
+    ports:
+    - 45678:45678
+    depends_on:
+    - selenium
+    - redis
+
+  selenium:
+    image: seleniarm/standalone-chromium
+    restart: unless-stopped
+    networks:
+    - default
+
+  redis:
+    image: redis:7.2
+    restart: unless-stopped
+    networks:
+    - default
+    volumes:
+    - redis-data:/data
+
+
+
+
+volumes:
+  redis-data:

railties/test/fixtures/.devcontainer/devcontainer.json

@@ -0,0 +1,34 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/ruby
+{
+  "name": "tmp",
+  "dockerComposeFile": "compose.yaml",
+  "service": "rails-app",
+  "workspaceFolder": "/workspaces/${localWorkspaceFolderBasename}",
+
+  // Features to add to the dev container. More info: https://containers.dev/features.
+  "features": {
+    "ghcr.io/devcontainers/features/github-cli:1": {}
+  },
+
+  "containerEnv": {
+    "CAPYBARA_SERVER_PORT": "45678",
+    "SELENIUM_HOST": "selenium",
+    "REDIS_URL": "redis://redis:6379/1"
+  },
+
+  // Features to add to the dev container. More info: https://containers.dev/features.
+  // "features": {},
+
+  // Use 'forwardPorts' to make a list of ports inside the container available locally.
+  // "forwardPorts": [],
+
+  // Configure tool-specific properties.
+  // "customizations": {},
+
+  // Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
+  // "remoteUser": "root",
+
+  // Use 'postCreateCommand' to run commands after the container is created.
+  "postCreateCommand": "bin/setup"
+}

railties/test/generators/app_generator_test.rb

@@ -5,6 +5,9 @@ require "rails/generators/rails/app/app_generator"
 require "generators/shared_generator_tests"
 
 DEFAULT_APP_FILES = %w(
+  .devcontainer/Dockerfile
+  .devcontainer/compose.yaml
+  .devcontainer/devcontainer.json
   .dockerignore
   .git
   .gitattributes
@@ -1005,11 +1008,17 @@ class AppGeneratorTest < Rails::Generators::TestCase
   def test_inclusion_of_ruby_version
     run_generator
 
+    ruby_version = "#{Gem::Version.new(Gem::VERSION) >= Gem::Version.new("3.3.13") ? Gem.ruby_version : RUBY_VERSION}"
+
     assert_file "Gemfile" do |content|
-      assert_match(/ruby "#{Gem::Version.new(Gem::VERSION) >= Gem::Version.new("3.3.13") ? Gem.ruby_version : RUBY_VERSION}"/, content)
+      assert_match("ruby \"#{ruby_version}\"", content)
+    end
+    assert_file ".devcontainer/Dockerfile" do |content|
+      minor_ruby_version = ruby_version.match(/^\d+\.\d+/).to_s
+      assert_match(/ARG RUBY_VERSION=#{minor_ruby_version}$/, content)
     end
     assert_file "Dockerfile" do |content|
-      assert_match(/ARG RUBY_VERSION=#{Gem::Version.new(Gem::VERSION) >= Gem::Version.new("3.3.13") ? Gem.ruby_version : RUBY_VERSION}/, content)
+      assert_match(/ARG RUBY_VERSION=#{ruby_version}/, content)
     end
     assert_file ".ruby-version" do |content|
       if ENV["RBENV_VERSION"]
@@ -1229,6 +1238,185 @@ class AppGeneratorTest < Rails::Generators::TestCase
     assert_file "config/application.rb", /^module MyApp$/
   end
 
+  def test_devcontainer
+    run_generator [destination_root, "--name=my-app"]
+
+    assert_file(".devcontainer/devcontainer.json") do |content|
+      assert_match(/"name": "my_app"/, content)
+      assert_match(/"REDIS_URL": "redis:\/\/redis:6379\/1"/, content)
+      assert_match(/"CAPYBARA_SERVER_PORT": "45678"/, content)
+      assert_match(/"SELENIUM_HOST": "selenium"/, content)
+    end
+    assert_file(".devcontainer/Dockerfile") do |content|
+      assert_match(/libvips/, content)
+      assert_match(/ffmpeg/, content)
+      assert_match(/poppler-utils/, content)
+    end
+    assert_compose_file do |compose_config|
+      expected_rails_app_config = {
+        "build" => {
+          "context" => "..",
+          "dockerfile" => ".devcontainer/Dockerfile"
+        },
+        "volumes" => ["../..:/workspaces:cached"],
+        "command" => "sleep infinity",
+        "networks" => ["default"],
+        "ports" => ["45678:45678"],
+        "depends_on" => ["selenium", "redis"]
+      }
+
+      assert_equal expected_rails_app_config, compose_config["services"]["rails-app"]
+
+      expected_selenium_conifg = {
+        "image" => "seleniarm/standalone-chromium",
+        "restart" => "unless-stopped",
+        "networks" => ["default"]
+      }
+
+      assert_equal expected_selenium_conifg, compose_config["services"]["selenium"]
+
+      expected_redis_config = {
+        "image" => "redis:7.2",
+        "restart" => "unless-stopped",
+        "networks" => ["default"],
+        "volumes" => ["redis-data:/data"]
+      }
+
+      assert_equal expected_redis_config, compose_config["services"]["redis"]
+      assert_equal ["redis-data"], compose_config["volumes"].keys
+    end
+  end
+
+  def test_devcontainer_no_redis_skipping_action_cable_and_active_job
+    run_generator [ destination_root, "--skip-action-cable", "--skip-active-job" ]
+
+    assert_compose_file do |compose_config|
+      assert_not_includes compose_config["services"]["rails-app"]["depends_on"], "redis"
+      assert_nil compose_config["services"]["redis"]
+      assert_nil compose_config["volumes"]
+    end
+  end
+
+  def test_devonctainer_postgresql
+    run_generator [ destination_root, "-d", "postgresql" ]
+
+    assert_compose_file do |compose_config|
+      assert_includes compose_config["services"]["rails-app"]["depends_on"], "postgres"
+
+      expected_postgres_config = {
+        "image" => "postgres:16.1",
+        "restart" => "unless-stopped",
+        "networks" => ["default"],
+        "volumes" => ["postgres-data:/var/lib/postgresql/data"],
+        "environment" => {
+          "POSTGRES_USER" => "postgres",
+          "POSTGRES_PASSWORD" => "postgres"
+        }
+      }
+
+      assert_equal expected_postgres_config, compose_config["services"]["postgres"]
+      assert_includes compose_config["volumes"].keys, "postgres-data"
+    end
+    assert_file(".devcontainer/devcontainer.json") do |content|
+      assert_match(/"DB_HOST": "postgres"/, content)
+    end
+    assert_file("config/database.yml") do |content|
+      assert_match(/host: <%= ENV\["DB_HOST"\] %>/, content)
+    end
+  end
+
+  def test_devonctainer_mysql
+    run_generator [ destination_root, "-d", "mysql" ]
+
+    assert_compose_file do |compose_config|
+      assert_includes compose_config["services"]["rails-app"]["depends_on"], "mysql"
+
+      expected_mysql_config = {
+        "image" => "mysql/mysql-server:8.0",
+        "restart" => "unless-stopped",
+        "environment" => {
+          "MYSQL_ALLOW_EMPTY_PASSWORD" => true,
+          "MYSQL_ROOT_HOST" => "%"
+        },
+        "volumes" => ["mysql-data:/var/lib/mysql"],
+        "networks" => ["default"],
+      }
+
+      assert_equal expected_mysql_config, compose_config["services"]["mysql"]
+      assert_includes compose_config["volumes"].keys, "mysql-data"
+    end
+    assert_file(".devcontainer/devcontainer.json") do |content|
+      assert_match(/"DB_HOST": "mysql"/, content)
+    end
+    assert_file("config/database.yml") do |content|
+      assert_match(/host: <%= ENV.fetch\("DB_HOST"\) \{ "localhost" } %>/, content)
+    end
+  end
+
+  def test_devonctainer_mariadb
+    run_generator [ destination_root, "-d", "trilogy" ]
+
+    assert_compose_file do |compose_config|
+      assert_includes compose_config["services"]["rails-app"]["depends_on"], "mariadb"
+      expected_mariadb_config = {
+        "image" => "mariadb:10.5",
+        "restart" => "unless-stopped",
+        "networks" => ["dqefault"],
+        "volumes" => ["mariadb-data:/var/lib/mysql"],
+        "environment" => {
+          "MARIADB_ALLOW_EMPTY_ROOT_PASSWORD" => true,
+        },
+      }
+
+      assert_equal expected_mariadb_config, compose_config["services"]["mariadb"]
+      assert_includes compose_config["volumes"].keys, "mariadb-data"
+    end
+    assert_file(".devcontainer/devcontainer.json") do |content|
+      assert_match(/"DB_HOST": "mariadb"/, content)
+    end
+    assert_file("config/database.yml") do |content|
+      assert_match(/host: <%= ENV.fetch\("DB_HOST"\) \{ "localhost" } %>/, content)
+    end
+  end
+
+  def test_devcontainer_no_selenium_when_skipping_system_test
+    run_generator [ destination_root, "--skip-system-test" ]
+
+    assert_compose_file do |compose_config|
+      assert_not_includes compose_config["services"]["rails-app"]["depends_on"], "selenium"
+      assert_not_includes compose_config["services"].keys, "selenium"
+    end
+    assert_file(".devcontainer/devcontainer.json") do |content|
+      assert_no_match(/CAPYBARA_SERVER_PORT/, content)
+    end
+  end
+
+  def test_devcontainer_no_Dockerfile_packages_when_skipping_active_storage
+    run_generator [ destination_root, "--skip-active-storage" ]
+
+    assert_file(".devcontainer/Dockerfile") do |content|
+      assert_no_match(/libvips/, content)
+      assert_no_match(/ffmpeg/, content)
+      assert_no_match(/poppler-utils/, content)
+    end
+  end
+
+  def test_devcontainer_no_depends_on_when_no_dependencies
+    run_generator [ destination_root, "--minimal" ]
+
+    assert_compose_file do |compose_config|
+      assert_not_includes compose_config["services"]["rails-app"].keys, "depends_on"
+    end
+  end
+
+  def test_skip_devcontainer
+    run_generator [ destination_root, "--skip-devcontainer" ]
+
+    assert_no_file(".devcontainer/devcontainer.json")
+    assert_no_file(".devcontainer/Dockerfile")
+    assert_no_file(".devcontainer/compose.yaml")
+  end
+
   private
     def assert_node_files
       assert_file ".node-version" do |content|

railties/test/generators/db_system_change_generator_test.rb

@@ -17,6 +17,7 @@ module Rails
             ENTRY
 
             copy_dockerfile
+            copy_devcontainer_files
           end
 
           test "change to invalid database" do
@@ -50,6 +51,28 @@ module Rails
               assert_match "build-essential git libpq-dev", content
               assert_match "curl libvips postgresql-client", content
             end
+
+            assert_file(".devcontainer/devcontainer.json") do |content|
+              assert_match(/"DB_HOST": "postgres"/, content)
+            end
+
+            assert_compose_file do |compose_config|
+              assert_includes compose_config["services"]["rails-app"]["depends_on"], "postgres"
+
+              expected_postgres_config = {
+                "image" => "postgres:16.1",
+                "restart" => "unless-stopped",
+                "networks" => ["default"],
+                "volumes" => ["postgres-data:/var/lib/postgresql/data"],
+                "environment" => {
+                  "POSTGRES_USER" => "postgres",
+                  "POSTGRES_PASSWORD" => "postgres"
+                }
+              }
+
+              assert_equal expected_postgres_config, compose_config["services"]["postgres"]
+              assert_includes compose_config["volumes"].keys, "postgres-data"
+            end
           end
 
           test "change to mysql" do
@@ -69,6 +92,28 @@ module Rails
               assert_match "build-essential default-libmysqlclient-dev git", content
               assert_match "curl default-mysql-client libvips", content
             end
+
+            assert_file(".devcontainer/devcontainer.json") do |content|
+              assert_match(/"DB_HOST": "mysql"/, content)
+            end
+
+            assert_compose_file do |compose_config|
+              assert_includes compose_config["services"]["rails-app"]["depends_on"], "mysql"
+
+              expected_postgres_config = {
+                "image" => "mysql/mysql-server:8.0",
+                "restart" => "unless-stopped",
+                "environment" => {
+                  "MYSQL_ALLOW_EMPTY_PASSWORD" => true,
+                  "MYSQL_ROOT_HOST" => "%"
+                },
+                "volumes" => ["mysql-data:/var/lib/mysql"],
+                "networks" => ["default"],
+              }
+
+              assert_equal expected_postgres_config, compose_config["services"]["mysql"]
+              assert_includes compose_config["volumes"].keys, "mysql-data"
+            end
           end
 
           test "change to sqlite3" do
@@ -88,6 +133,10 @@ module Rails
               assert_match "build-essential git", content
               assert_match "curl libsqlite3-0 libvips", content
             end
+
+            assert_file(".devcontainer/devcontainer.json") do |content|
+              assert_no_match(/"DB_HOST"/, content)
+            end
           end
 
           test "change to trilogy" do
@@ -108,6 +157,27 @@ module Rails
               assert_match "curl libvips", content
               assert_no_match "default-libmysqlclient-dev", content
             end
+
+            assert_file(".devcontainer/devcontainer.json") do |content|
+              assert_match(/"DB_HOST": "mariadb"/, content)
+            end
+
+            assert_compose_file do |compose_config|
+              assert_includes compose_config["services"]["rails-app"]["depends_on"], "mariadb"
+
+              expected_postgres_config = {
+                "image" => "mariadb:10.5",
+                "restart" => "unless-stopped",
+                "networks" => ["dqefault"],
+                "volumes" => ["mariadb-data:/var/lib/mysql"],
+                "environment" => {
+                  "MARIADB_ALLOW_EMPTY_ROOT_PASSWORD" => true,
+                },
+              }
+
+              assert_equal expected_postgres_config, compose_config["services"]["mariadb"]
+              assert_includes compose_config["volumes"].keys, "mariadb-data"
+            end
           end
 
           test "change from versioned gem to other versioned gem" do
@@ -124,6 +194,23 @@ module Rails
               assert_match 'gem "mysql2", "~> 0.5"', content
             end
           end
+
+          test "change from db with devcontainer service to one without" do
+            copy_minimal_devcontainer_compose_file
+
+            run_generator ["--to", "mysql"]
+            run_generator ["--to", "sqlite3", "--force"]
+
+            assert_file(".devcontainer/devcontainer.json") do |content|
+              assert_no_match(/"DB_HOST"/, content)
+            end
+
+            assert_compose_file do |compose_config|
+              assert_not_includes compose_config["services"]["rails-app"].keys, "depends_on"
+              assert_not_includes compose_config["services"].keys, "mysql"
+              assert_not_includes compose_config.keys, "volumes"
+            end
+          end
         end
       end
     end

railties/test/generators/generators_test_helper.rb

@@ -82,6 +82,25 @@ module GeneratorsTestHelper
     File.write File.join(destination, "Dockerfile"), dockerfile
   end
 
+  def copy_devcontainer_files
+    destination = File.join(destination_root, ".devcontainer")
+    mkdir_p(destination)
+
+    devcontainer_json = File.read(File.expand_path("../fixtures/.devcontainer/devcontainer.json", __dir__))
+    File.write File.join(destination, "devcontainer.json"), devcontainer_json
+
+    compose_yaml = File.read(File.expand_path("../fixtures/.devcontainer/compose.yaml", __dir__))
+    File.write File.join(destination, "compose.yaml"), compose_yaml
+  end
+
+  def copy_minimal_devcontainer_compose_file
+    destination = File.join(destination_root, ".devcontainer")
+    mkdir_p(destination)
+
+    compose_yaml = File.read(File.expand_path("../fixtures/.devcontainer/compose-minimal.yaml", __dir__))
+    File.write File.join(destination, "compose.yaml"), compose_yaml
+  end
+
   def evaluate_template(file, locals = {})
     erb = ERB.new(File.read(file), trim_mode: "-", eoutvar: "@output_buffer")
     context = Class.new do
@@ -97,6 +116,12 @@ module GeneratorsTestHelper
     erb.result()
   end
 
+  def assert_compose_file
+    assert_file ".devcontainer/compose.yaml" do |content|
+      yield YAML.load(content)
+    end
+  end
+
   private
     def gemfile_locals
       {