Raise error with tip when required ActionView context is missing

lib/phlex/rails/sgml.rb

@@ -11,10 +11,10 @@ def render_in(...)
 
 			module Overrides
 				def helpers
-					if defined?(ViewComponent::Base) && ViewComponent::Base === @_view_context
-						@_view_context.helpers
+					if defined?(ViewComponent::Base) && ViewComponent::Base === view_context!
+						view_context!.helpers
 					else
-						@_view_context
+						view_context!
 					end
 				end
 
@@ -33,23 +33,23 @@ def render(*args, **kwargs, &block)
 
 						if partial # this is a hack to get around https://github.com/rails/rails/issues/51015
 							return raw(
-								@_view_context.render(partial, **kwargs) do |*yielded_args|
+								view_context!.render(partial, **kwargs) do |*yielded_args|
 									capture(*yielded_args, &block)
 								end,
 							)
 						end
 					end
 
 					output = if block
-						@_view_context.render(*args, **kwargs) do |*yielded_args|
+						view_context!.render(*args, **kwargs) do |*yielded_args|
 							if yielded_args.length == 1 && defined?(ViewComponent::Base) && ViewComponent::Base === yielded_args[0]
 								capture(Phlex::Rails::Buffered.new(yielded_args[0], view: self), &block)
 							else
 								capture(*yielded_args, &block)
 							end
 						end
 					else
-						@_view_context.render(*args, **kwargs)
+						view_context!.render(*args, **kwargs)
 					end
 
 					raw(output)
@@ -82,6 +82,20 @@ def capture(...)
 				# @api private
 				def set_original_view_context(view_context)
 				end
+
+				private
+
+				def view_context!
+					unless @_view_context
+						instance_name = "#{self.class.name.sub(/::[^:]+\z/, '')}_instance"
+						err_s = "👋 Please use `render` to render #{self.class.name} instances (instead of " \
+							"`#{instance_name}.call`). Using `render` allows the component to receive the " \
+							"ActionView context, which is required by Phlex helpers it includes."
+						raise StandardError.new(err_s)
+					end
+
+					@_view_context
+				end
 			end
 		end
 	end

test/dummy/app/controllers/helpers_controller.rb

@@ -19,4 +19,13 @@ def notice_test # can't use 'notice' as the method name because it interferes wi
 		flash.now.notice = "My Flash Notice"
 		render Helpers::NoticeView.new
 	end
+
+	def view_context_required
+		case params[:render_style]
+		when "call"
+			Helpers::ViewContextRequired.new.call
+		when "render"
+			render Helpers::ViewContextRequired.new
+		end
+	end
 end

test/dummy/app/views/helpers/view_context_required.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class Helpers::ViewContextRequired < ApplicationView
+	include ActionView::Helpers::UrlHelper
+
+	def view_template
+		# root_path will fail unless the view context has been set.
+		p { root_path }
+	end
+end

test/dummy/config/routes.rb

@@ -17,6 +17,7 @@
 	get "/helpers/tag", to: "helpers#tag"
 	get "/helpers/missing_helper", to: "helpers#missing_helper"
 	get "/helpers/notice", to: "helpers#notice_test"
+	get "/helpers/view_context_required", to: "helpers#view_context_required"
 
 	get "/rendering/partial_from_phlex", to: "rendering#partial_from_phlex"
 	get "/rendering/view_component_from_phlex", to: "rendering#view_component_from_phlex"

test/phlex/helpers_test.rb

@@ -34,4 +34,15 @@ class HelpersTest < ActionDispatch::IntegrationTest
 		assert_response :success
 		assert_select "div > h1#hello.text-xl", "Hello World"
 	end
+
+	test "view_context required" do
+		get "/helpers/view_context_required?render_style=render"
+		assert_response :success
+		assert_select "p", "/"
+
+		exception = assert_raises(StandardError) do
+			get "/helpers/view_context_required?render_style=call"
+		end
+		assert_includes exception.message, "Please use `render`"
+	end
 end