Fix deprecations on ActiveModel::Errors (#3869)

* Fix deprecation: ActiveModel::Errors#to_xml

* Fix: Enumerating ActiveModel::Errors as a hash

app/controllers/admin/api/signups_controller.rb

@@ -25,8 +25,8 @@ def check_creation_errors
     # and not respond with pathetic error
     raise ActiveRecord::RecordNotFound if @signup_result.errors[:plans].present?
 
-    @signup_result.user.errors.each do |attr, error|
-      @signup_result.account.errors.add(attr, error)
+    @signup_result.user.errors.each do |error|
+      @signup_result.account.errors.add(error.attribute, error.message)
     end
   end
 

app/lib/three_scale/errors_to_xml.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+module ThreeScale
+  module ErrorsToXml
+    # This was deprecated with no replacement in rails 6. Because allegedly
+    # nobody uses it. So we have to keep a copy until we completely stop
+    # supporting XMLs in our APIs.
+    # https://github.com/rails/rails/pull/32313
+    #
+    # Returns an xml formatted representation of the Errors hash.
+    #
+    #   person.errors.add(:name, :blank, message: "can't be blank")
+    #   person.errors.add(:name, :not_specified, message: "must be specified")
+    #   person.errors.to_xml
+    #   # =>
+    #   #  <?xml version=\"1.0\" encoding=\"UTF-8\"?>
+    #   #  <errors>
+    #   #    <error>name can't be blank</error>
+    #   #    <error>name must be specified</error>
+    #   #  </errors>
+    def to_xml(options = {})
+      to_a.to_xml({ root: "errors", skip_types: true }.merge!(options))
+    end
+  end
+end

config/initializers/active_model.rb

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+Rails.application.config.to_prepare do
+  ActiveModel::Errors.prepend ThreeScale::ErrorsToXml
+end