Backport delegate_missing_to from Rails 5.1

Author: ysbaddaden

app/models/box_form.rb

@@ -2,7 +2,7 @@ class BoxForm
   attr_reader :box, :batch_uuids
 
   delegate :purpose, :purpose=, to: :box
-  delegate :model_name, :errors, to: :box
+  delegate_missing_to :box
 
   def self.build(navigation_context, params = nil)
     box = Box.new(

app/presenters/sample_transfer_presenter.rb

@@ -1,14 +1,13 @@
 class SampleTransferPresenter
   attr_reader :transfer, :context, :current_user
 
+  delegate_missing_to :transfer
+
   def initialize(transfer, context)
     @transfer = transfer
     @context = context
   end
 
-  # TODO(Rails 5.1): Use delegate_missing
-  delegate :transfer_package, :sample, :confirmed_at, :confirmed?, :created_at, :receiver_institution, :sender_institution, to: :transfer
-
   def receiver?
     context.institution == transfer.receiver_institution
   end

app/views/boxes/_form.haml

@@ -1,4 +1,4 @@
-= cdx_form_for(@box_form.box) do |f|
+= cdx_form_for(@box_form) do |f|
   .row
     .col
       = f.form_field :purpose do

config/initializers/backports.rb

@@ -0,0 +1 @@
+require "delegate_missing_to"

lib/delegate_missing_to.rb

@@ -0,0 +1,27 @@
+# Backports `#delegate_missing_to` from Rails 5.1
+
+unless Module.respond_to?(:delegate_missing_to)
+  class Module
+    def delegate_missing_to(target)
+      target = target.to_s
+      target = "self.#{target}" if DELEGATION_RESERVED_METHOD_NAMES.include?(target)
+
+      module_eval <<-RUBY, __FILE__, __LINE__ + 1
+        def respond_to_missing?(name, include_private = false)
+          # It may look like an oversight, but we deliberately do not pass
+          # +include_private+, because they do not get delegated.
+
+          #{target}.respond_to?(name) || super
+        end
+
+        def method_missing(method, *args, &block)
+          if #{target}.respond_to?(method)
+            #{target}.public_send(method, *args, &block)
+          else
+            super
+          end
+        end
+        RUBY
+    end
+  end
+end