FIX: Validate interpolation keys used in translation overrides.

https://meta.discourse.org/t/discobot-translation-missing-error/64429/6?u=tgxworld

app/models/translation_override.rb

@@ -1,9 +1,12 @@
 require 'js_locale_helper'
+require "i18n/i18n_interpolation_keys_finder"
 
 class TranslationOverride < ActiveRecord::Base
   validates_uniqueness_of :translation_key, scope: :locale
   validates_presence_of :locale, :translation_key, :value
 
+  validate :check_interpolation_keys
+
   def self.upsert!(locale, key, value)
     params = { locale: locale, translation_key: key }
 
@@ -12,9 +15,10 @@ class TranslationOverride < ActiveRecord::Base
       data[:compiled_js] = JsLocaleHelper.compile_message_format(locale, value)
     end
 
-    row_count = where(params).update_all(data)
-    create!(params.merge(data)) if row_count == 0
-    i18n_changed
+    translation_override = find_or_initialize_by(params)
+    params.merge!(data) if translation_override.new_record?
+    i18n_changed if translation_override.update(data)
+    translation_override
   end
 
   def self.revert!(locale, *keys)
@@ -22,13 +26,48 @@ class TranslationOverride < ActiveRecord::Base
     i18n_changed
   end
 
-  protected
+  private
 
     def self.i18n_changed
       I18n.reload!
       MessageBus.publish('/i18n-flush', { refresh: true })
     end
 
+    def lookup_original_text
+      I18n::Backend::Simple.new.send(
+        :lookup, self.locale, self.translation_key
+      )
+    end
+
+    def check_interpolation_keys
+      if original_text = lookup_original_text
+        original_interpolation_keys = I18nInterpolationKeysFinder.find(original_text)
+        new_interpolation_keys = I18nInterpolationKeysFinder.find(value)
+        missing_keys = (original_interpolation_keys - new_interpolation_keys)
+        invalid_keys = (original_interpolation_keys | new_interpolation_keys) - original_interpolation_keys
+
+        if missing_keys.present?
+          self.errors.add(:base, I18n.t(
+            'activerecord.errors.models.translation_overrides.attributes.value.missing_interpolation_keys',
+            keys: missing_keys.join(', ')
+          ))
+
+          return false
+        end
+
+        invalid_keys = (original_interpolation_keys | new_interpolation_keys) - original_interpolation_keys
+
+        if invalid_keys.present?
+          self.errors.add(:base, I18n.t(
+            'activerecord.errors.models.translation_overrides.attributes.value.invalid_interpolation_keys',
+            keys: invalid_keys.join(', ')
+          ))
+
+          return false
+        end
+      end
+    end
+
 end
 
 # == Schema Information