locale query params for session_locale

fixes CAT-330

NOTE: *the locale for a page is inferred in a weighted order.
       session_locale is checked just before a provided context's
       account locale preference and just after the user's

Test Plan
  1. Fire up canvas with full i18n support configured
     (i.e. $ RAILS_LOAD_ALL_LOCALES=true rails server)
  2. Navigate to a page that supports localization while logged out
     such as the login screen
  3. Append the following query params to the URL in the browser
     '?session_locale=zh'
  4. Navigate to that URL and ensure the page is localized in the provided
     locale

Change-Id: I9e94d6ecfd41e77683940272aa0988c67064b602
Reviewed-on: https://gerrit.instructure.com/39844
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Ethan Gunderson <egunderson@instructure.com>
Reviewed-by: Nick Houle <nhoule@instructure.com>
Product-Review: Adam Phillipps <adam@instructure.com>
QA-Review: Adam Phillipps <adam@instructure.com>

app/controllers/application_controller.rb

@@ -184,17 +184,25 @@ class ApplicationController < ActionController::Base
       infer_locale :context => @context,
                    :user => @current_user,
                    :root_account => @domain_root_account,
+                   :session_locale => session[:locale],
                    :accept_language => request.headers['Accept-Language']
     }
   end
 
   def set_locale
+    store_session_locale
     assign_localizer
     yield if block_given?
   ensure
     I18n.localizer = nil
   end
 
+  def store_session_locale
+    return unless locale = params[:session_locale]
+    supported_locales = I18n.available_locales.map(&:to_s)
+    session[:locale] = locale if supported_locales.include? locale
+  end
+
   def init_body_classes
     @body_classes = []
   end

lib/locale_selection.rb

@@ -4,6 +4,7 @@ module LocaleSelection
     user = options[:user]
     root_account = options[:root_account]
     accept_language = options[:accept_language]
+    session_locale = options[:session_locale]
 
     # groups cheat and set the context to be the group after get_context runs
     # but before set_locale runs, but we want to do locale lookup based on the
@@ -16,6 +17,8 @@ module LocaleSelection
       context.locale
     elsif user && user.locale
       user.locale
+    elsif session_locale
+      session_locale
     elsif context && context.is_a?(Course) && context.account && (account_locale = context.account.default_locale(true))
       account_locale
     elsif context && context.is_a?(Account) && (account_locale = context.default_locale(true))

spec/lib/locale_selection_spec.rb

@@ -89,7 +89,7 @@ describe LocaleSelection do
 
   context "locale matching" do
     before do
-      I18n.stubs(:available_locales).returns([:en, :it, :es, :fr, :de, :pt])
+      I18n.stubs(:available_locales).returns([:en, :it, :es, :fr, :de, :pt, :zh])
       @root_account = Account.create
       @account = Account.create(:parent_account => @root_account)
       user
@@ -164,5 +164,14 @@ describe LocaleSelection do
       ls.infer_locale(:accept_language => "it", :root_account => @root_account, :user => @user, :context => account_gr).should eql('fr')
       ls.infer_locale(:accept_language => "it", :root_account => @root_account, :user => @user, :context => course_gr).should eql('es')
     end
+
+    it "should infer the locale from the session" do
+      @root_account.update_attribute(:default_locale, 'es')
+      @account.update_attribute(:default_locale, 'fr')
+      @user.update_attribute(:locale, 'de')
+
+      ls.infer_locale(:accept_language => "it", :root_account => @root_account, :context => @account, :session_locale => 'zh').should eql('zh')
+      ls.infer_locale(:accept_language => "it", :root_account => @root_account, :context => @account, :user => @user, :session_locale => 'zh').should eql('de')
+    end
   end
 end