Add mechanism for component-local inheritable config

Preview namespace additionally added to config object in this commit to test config inheritance.
Much more cleanup to be done around making as many things as possible component-local.

Author: boardfish

lib/view_component/base.rb

@@ -19,14 +19,16 @@
 
 module ViewComponent
   class Base < ActionView::Base
+    # Returns the current config.
+    #
+    # @return [ActiveSupport::OrderedOptions]
+    class_attribute :config, default: ViewComponent::Config.defaults
+
     class << self
       delegate(*ViewComponent::Config.defaults.keys, to: :config)
 
-      # Returns the current config.
-      #
-      # @return [ActiveSupport::OrderedOptions]
-      def config
-        ViewComponent::Config.current
+      def configure(&block)
+        config.instance_eval(&block)
       end
     end
 
@@ -40,7 +42,7 @@ def config
     VC_INTERNAL_DEFAULT_FORMAT = :html
 
     # For CSRF authenticity tokens in forms
-    delegate :form_authenticity_token, :protect_against_forgery?, :config, to: :helpers
+    delegate :form_authenticity_token, :protect_against_forgery?, to: :helpers
 
     # For Content Security Policy nonces
     delegate :content_security_policy_nonce, to: :helpers

lib/view_component/config.rb

@@ -15,6 +15,9 @@ def defaults
           generate: default_generate_options,
           preview_controller: "ViewComponentsController",
           preview_route: "/rails/view_components",
+          preview: ActiveSupport::OrderedOptions.new({
+            paths: default_preview_paths
+          }),
           show_previews_source: false,
           instrumentation_enabled: false,
           use_deprecated_instrumentation_name: true,

test/sandbox/app/components/config_base_component.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class ConfigBaseComponent < ViewComponent::Base
+  configure do
+    preview.paths = ["expected_path"]
+  end
+end

test/sandbox/app/components/inherited_config_component.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class InheritedConfigComponent < ConfigBaseComponent
+  configure do
+    preview.paths << "another_expected_path"
+  end
+end

test/sandbox/test/base_test.rb

@@ -145,4 +145,18 @@ def test_no_method_error_does_not_reference_missing_helper
     MESSAGE
     assert !exception_message_regex.match?(exception.message)
   end
+
+  def test_configuration_dsl
+    component_class = Class.new(ViewComponent::Base) do
+      configure do
+        preview.paths = ["expected_path"]
+      end
+    end
+
+    assert_equal ConfigBaseComponent.new.config.preview.paths, ["expected_path"]
+  end
+
+  def test_inherited_configuration
+    assert_equal InheritedConfigComponent.new.config.preview.paths, ["expected_path", "another_expected_path"]
+  end
 end