Use devcontainer features for optional dependencies

We have created our own features for optional Rails dependencies needed for active storage, postgres and mysql. Features provide a bit better ergonomics for adding or removing these from the devcontainer, and previously we were always installing these dependencies via the devcontainer's dockerfile, whether the app was using them or not.

With this change, when we generate the app, we just add the features we need to the devcontainer.json. And also, we swap features in and out as need when doing db:system:change.

railties/lib/rails/generators/devcontainer.rb

@@ -39,6 +39,19 @@ def devcontainer_volumes
           @devcontainer_volumes
         end
 
+        def devcontainer_features
+          return @devcontainer_features if @devcontainer_features
+
+          @devcontainer_features = {
+            "ghcr.io/devcontainers/features/github-cli:1" => {}
+          }
+
+          @devcontainer_features["ghcr.io/rails/devcontainer/features/activestorage"] = {} unless options[:skip_active_storage]
+          @devcontainer_features.merge!(db_feature_for_devcontainer) if db_feature_for_devcontainer
+
+          @devcontainer_features
+        end
+
         def devcontainer_mounts
           return @devcontainer_mounts if @devcontainer_mounts
 
@@ -90,6 +103,13 @@ def db_service_for_devcontainer(database = options[:database])
           end
         end
 
+        def db_feature_for_devcontainer(database = options[:database])
+          case database
+          when "mysql"          then mysql_feature
+          when "postgresql"     then postgres_feature
+          end
+        end
+
         def postgres_service
           {
             "postgres" => {
@@ -138,6 +158,21 @@ def db_service_names
           ["mysql", "mariadb", "postgres"]
         end
 
+        def mysql_feature
+          { "ghcr.io/rails/devcontainer/features/mysql-client" => {} }
+        end
+
+        def postgres_feature
+          { "ghcr.io/rails/devcontainer/features/postgres-client" => {} }
+        end
+
+        def db_features
+          [
+            "ghcr.io/rails/devcontainer/features/mysql-client",
+            "ghcr.io/rails/devcontainer/features/postgres-client"
+          ]
+        end
+
         def local_rails_mount
           {
             type: "bind",

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

@@ -1,16 +1,3 @@
 # Make sure RUBY_VERSION matches the Ruby version in .ruby-version
 ARG RUBY_VERSION=<%= gem_ruby_version %>
 FROM ghcr.io/rails/devcontainer/images/ruby:$RUBY_VERSION
-
-<%- unless options.skip_active_storage -%>
-# Install packages needed to build gems
-RUN apt-get update -qq && \
-    apt-get install --no-install-recommends -y \
-      <%= db_package_for_dockerfile %> 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/devcontainer.json.tt

@@ -8,7 +8,7 @@
 
   // Features to add to the dev container. More info: https://containers.dev/features.
   "features": {
-    "ghcr.io/devcontainers/features/github-cli:1": {}
+    <%= devcontainer_features.map { |key, value| "\"#{key}\": #{value}" }.join(",\n    ") %>
   },
 
 <%- if !devcontainer_variables.empty? -%>

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

@@ -101,27 +101,10 @@ def gem_entry_for(*gem_name_and_version)
             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
+              return unless devcontainer_json
 
-              new_json = JSON.pretty_generate(container_env, indent: "  ", object_nl: "\n  ")
-
-              gsub_file(".devcontainer/devcontainer.json", /("containerEnv"\s*:\s*){[^}]*}/, "\\1#{new_json}")
+              update_devcontainer_db_host
+              update_devcontainer_db_feature
             end
 
             def edit_compose_yaml
@@ -152,6 +135,52 @@ def edit_compose_yaml
 
               File.write(compose_yaml_path, compose_config.to_yaml)
             end
+
+            def update_devcontainer_db_host
+              container_env = devcontainer_json["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*)(.|\n)*?(^\s{2}})/, "\\1#{new_json}")
+            end
+
+            def update_devcontainer_db_feature
+              features = devcontainer_json["features"]
+              db_feature = db_feature_for_devcontainer
+
+              db_features.each do |feature|
+                features.delete(feature)
+              end
+
+              features.merge!(db_feature) if db_feature
+
+              new_json = JSON.pretty_generate(features, indent: "  ", object_nl: "\n  ")
+
+              gsub_file(".devcontainer/devcontainer.json", /("features"\s*:\s*)(.|\n)*?(^\s{2}})/, "\\1#{new_json}")
+            end
+
+            def devcontainer_json
+              return unless File.exist?(devcontainer_json_path)
+
+              @devcontainer_json ||= JSON.parse(File.read(devcontainer_json_path))
+            end
+
+            def devcontainer_json_path
+              File.expand_path(".devcontainer/devcontainer.json", destination_root)
+            end
         end
       end
     end

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

@@ -17,9 +17,6 @@
     "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": [],
 

railties/test/generators/app_generator_test.rb

@@ -1241,16 +1241,16 @@ def test_name_option
   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)
+    assert_devcontainer_json_file do |content|
+      assert_equal "my_app", content["name"]
+      assert_equal "redis://redis:6379/1", content["containerEnv"]["REDIS_URL"]
+      assert_equal "45678", content["containerEnv"]["CAPYBARA_SERVER_PORT"]
+      assert_equal "selenium", content["containerEnv"]["SELENIUM_HOST"]
+      assert_equal({}, content["features"]["ghcr.io/rails/devcontainer/features/activestorage"])
+      assert_equal({}, content["features"]["ghcr.io/devcontainers/features/github-cli:1"])
     end
     assert_file(".devcontainer/Dockerfile") do |content|
-      assert_match(/libvips/, content)
-      assert_match(/ffmpeg/, content)
-      assert_match(/poppler-utils/, content)
+      assert_match(/ARG RUBY_VERSION=#{RUBY_VERSION}/, content)
     end
     assert_compose_file do |compose_config|
       expected_rails_app_config = {
@@ -1317,15 +1317,13 @@ def test_devonctainer_postgresql
       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)
+    assert_devcontainer_json_file do |content|
+      assert_equal "postgres", content["containerEnv"]["DB_HOST"]
+      assert_equal({}, content["features"]["ghcr.io/rails/devcontainer/features/postgres-client"])
     end
     assert_file("config/database.yml") do |content|
       assert_match(/host: <%= ENV\["DB_HOST"\] %>/, content)
     end
-    assert_file(".devcontainer/Dockerfile") do |content|
-      assert_match(/libpq-dev/, content)
-    end
   end
 
   def test_devonctainer_mysql
@@ -1348,15 +1346,13 @@ def test_devonctainer_mysql
       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)
+    assert_devcontainer_json_file do |content|
+      assert_equal "mysql", content["containerEnv"]["DB_HOST"]
+      assert_equal({}, content["features"]["ghcr.io/rails/devcontainer/features/mysql-client"])
     end
     assert_file("config/database.yml") do |content|
       assert_match(/host: <%= ENV.fetch\("DB_HOST"\) \{ "localhost" } %>/, content)
     end
-    assert_file(".devcontainer/Dockerfile") do |content|
-      assert_match(/default-libmysqlclient-dev/, content)
-    end
   end
 
   def test_devonctainer_mariadb
@@ -1377,8 +1373,8 @@ def test_devonctainer_mariadb
       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)
+    assert_devcontainer_json_file do |content|
+      assert_equal "mariadb", content["containerEnv"]["DB_HOST"]
     end
     assert_file("config/database.yml") do |content|
       assert_match(/host: <%= ENV.fetch\("DB_HOST"\) \{ "localhost" } %>/, content)
@@ -1392,18 +1388,16 @@ def test_devcontainer_no_selenium_when_skipping_system_test
       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)
+    assert_devcontainer_json_file do |content|
+      assert_nil content["containerEnv"]["CAPYBARA_SERVER_PORT"]
     end
   end
 
-  def test_devcontainer_no_Dockerfile_packages_when_skipping_active_storage
+  def test_devcontainer_no_feature_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)
+    assert_devcontainer_json_file do |content|
+      assert_nil content["features"]["ghcr.io/rails/devcontainer/features/activestorage"]
     end
   end
 

railties/test/generators/db_system_change_generator_test.rb

@@ -54,6 +54,7 @@ class ChangeGeneratorTest < Rails::Generators::TestCase
 
             assert_file(".devcontainer/devcontainer.json") do |content|
               assert_match(/"DB_HOST": "postgres"/, content)
+              assert_match(/"ghcr.io\/rails\/devcontainer\/features\/postgres-client":/, content)
             end
 
             assert_compose_file do |compose_config|
@@ -95,6 +96,7 @@ class ChangeGeneratorTest < Rails::Generators::TestCase
 
             assert_file(".devcontainer/devcontainer.json") do |content|
               assert_match(/"DB_HOST": "mysql"/, content)
+              assert_match(/"ghcr.io\/rails\/devcontainer\/features\/mysql-client":/, content)
             end
 
             assert_compose_file do |compose_config|
@@ -203,6 +205,7 @@ class ChangeGeneratorTest < Rails::Generators::TestCase
 
             assert_file(".devcontainer/devcontainer.json") do |content|
               assert_no_match(/"DB_HOST"/, content)
+              assert_no_match(/"ghcr.io\/rails\/devcontainer\/features\/mysql-client":/, content)
             end
 
             assert_compose_file do |compose_config|