Fix zeitwerk issue

lib/action_view/template/handlers/prawn.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require 'prawn'
+
+module ActionView
+  module Template::Handlers
+    class Prawn
+      def self.register!
+        ::ActionView::Template.register_template_handler :prawn, self
+      end
+
+      def self.call(template, source = template.source)
+        %(extend #{::DocumentProxy}; #{source}; pdf.render)
+      end
+
+      module DocumentProxy
+        def pdf
+          @pdf ||= ::Prawn::Document.new(::Spree::PrintInvoice::Config[:prawn_options])
+        end
+
+        private
+
+        def method_missing(method, *args, &block)
+          pdf.respond_to?(method) ? pdf.send(method, *args, &block) : super
+        end
+      end
+    end
+  end
+end
+
+::ActionView::Template::Handlers::Prawn.register!

lib/solidus_print_invoice.rb

@@ -3,7 +3,7 @@
 require 'solidus_print_invoice/version'
 require 'solidus_print_invoice/engine'
 
-require 'prawn_handler'
+require 'action_view/template/handlers/prawn'
 
 module Spree
   module PrintInvoice