Add option to set default app layout for previews

Add integration test

Update Changelog

Fix test error for no layout previews

Refactor logic for determining preview layout

Better wording of method comment

Fix rebase merge issue

Move custom layout tests into separate file

Incorporate feedback from juanmanuelramallo

Fix for "interpreted as argument prefix" warning

Add render string back in for index action

CHANGELOG.md

@@ -1,5 +1,9 @@
 # master
 
+* Add `default_preview_layout` configuration option to load custom app/views/layouts.
+
+    *Jared White, Juan Manuel Ramallo*
+
 # 2.17.0
 
 * Slots return stripped HTML, removing leading and trailing whitespace.

app/controllers/view_components_controller.rb

@@ -16,18 +16,19 @@ class ViewComponentsController < Rails::ApplicationController # :nodoc:
   def index
     @previews = ViewComponent::Preview.all
     @page_title = "Component Previews"
+    render "view_components/index", **determine_layout
   end
 
   def previews
     if params[:path] == @preview.preview_name
       @page_title = "Component Previews for #{@preview.preview_name}"
-      render "view_components/previews"
+      render "view_components/previews", **determine_layout
     else
       prepend_application_view_paths
       prepend_preview_examples_view_path
       @example_name = File.basename(params[:path])
       @render_args = @preview.render_args(@example_name, params: params.permit!)
-      layout = @render_args[:layout]
+      layout = determine_layout(@render_args[:layout])[:layout]
       template = @render_args[:template]
       locals = @render_args[:locals]
       opts = {}
@@ -39,6 +40,10 @@ class ViewComponentsController < Rails::ApplicationController # :nodoc:
 
   private
 
+  def default_preview_layout # :doc:
+    ViewComponent::Base.default_preview_layout
+  end
+
   def show_previews? # :doc:
     ViewComponent::Base.show_previews
   end
@@ -61,6 +66,22 @@ class ViewComponentsController < Rails::ApplicationController # :nodoc:
     end
   end
 
+  # Returns either {} or {layout: value} depending on configuration
+  def determine_layout(layout_override = nil)
+    return {} unless defined?(Rails.root)
+
+    layout_declaration = {}
+
+    if !layout_override.nil?
+      # Allow component-level override, even if false (thus no layout rendered)
+      layout_declaration[:layout] = layout_override
+    elsif default_preview_layout.present?
+      layout_declaration[:layout] = default_preview_layout
+    end
+
+    layout_declaration
+  end
+
   def prepend_application_view_paths
     prepend_view_path Rails.root.join("app/views") if defined?(Rails.root)
   end

lib/view_component/previewable.rb

@@ -7,6 +7,14 @@ module ViewComponent # :nodoc:
     extend ActiveSupport::Concern
 
     included do
+      # Set a custom default preview layout through app configuration:
+      #
+      #     config.view_component.default_preview_layout = "component_preview"
+      #
+      # This affects preview index pages as well as individual component previews
+      #
+      mattr_accessor :default_preview_layout, instance_writer: false
+
       # Set the location of component previews through app configuration:
       #
       #     config.view_component.preview_paths << "#{Rails.root}/lib/component_previews"

test/test_helper.rb

@@ -41,3 +41,10 @@ def modify_file(file, content)
     File.open(filename, "wb+") { |f| f.write(old_content) }
   end
 end
+
+def with_default_preview_layout(layout)
+  old_value = ViewComponent::Base.default_preview_layout
+  ViewComponent::Base.default_preview_layout = layout
+  yield
+  ViewComponent::Base.default_preview_layout = old_value
+end

test/view_component/default_preview_layout_integration_test.rb

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class DefaultPreviewLayoutIntegrationTest < ActionDispatch::IntegrationTest
+  test "preview index renders custom application layout if configured" do
+    with_default_preview_layout("admin") do
+      get "/rails/view_components"
+      assert_select "title", "ViewComponent - Admin - Test"
+    end
+  end
+
+  test "preview index of a component renders custom application layout if configured" do
+    with_default_preview_layout("admin") do
+      get "/rails/view_components/preview_component"
+      assert_select "title", "ViewComponent - Admin - Test"
+    end
+  end
+
+  test "component preview renders custom application layout if configured" do
+    with_default_preview_layout("admin") do
+      get "/rails/view_components/preview_component/default"
+      assert_select "title", "ViewComponent - Admin - Test"
+      assert_select ".preview-component .btn", "Click me!"
+    end
+  end
+
+  test "component preview renders standard Rails layout if configured false" do
+    with_default_preview_layout(false) do
+      get "/rails/view_components/preview_component/default"
+
+      assert_select "title", "ViewComponent - Test"
+      assert_select ".preview-component .btn", "Click me!"
+    end
+  end
+
+  test "preview renders without layout even if default layout is configured" do
+    with_default_preview_layout("admin") do
+      get "/rails/view_components/no_layout/default"
+      assert_select("div", "hello,world!")
+      refute_includes response.body, "ViewComponent - Admin - Test"
+    end
+  end
+end

test/view_component/integration_test.rb

@@ -281,6 +281,7 @@ class IntegrationTest < ActionDispatch::IntegrationTest
     get "/rails/view_components/no_layout/default"
 
     assert_select("div", "hello,world!")
+    refute_includes response.body, "ViewComponent - Test"
   end
 
   test "test preview renders application's layout by default" do