Skip header parsing when set_locale gets a single locale

lib/fast_gettext/storage.rb

@@ -134,7 +134,8 @@ def default_locale
     # IE6/7 de
     # nil if nothing matches
     def best_locale_in(locales)
-      formatted_sorted_locales(locales).each do |candidate|
+      candidates = plain_locale(locales) || formatted_sorted_locales(locales)
+      candidates.each do |candidate|
         return candidate unless available_locales
         return candidate if available_locales.include?(candidate)
         return candidate[0..1] if available_locales.include?(candidate[0..1]) # available locales include a langauge
@@ -160,6 +161,15 @@ def silence_errors
 
     private
 
+    # A single locale already in the de / de_DE form, as set_locale gets it on
+    # every I18n.locale= or with_locale (gettext_i18n_rails): parsing it as
+    # an Accept-Language header would give the same one candidate.
+    PLAIN_LOCALE = /\A[a-z]{2,3}(?:_[A-Z]{2,3})?\z/
+    def plain_locale(locale)
+      locale = locale.name if locale.is_a?(Symbol)
+      [locale.dup] if locale.is_a?(String) && PLAIN_LOCALE.match?(locale)
+    end
+
     # de-de,DE-CH;q=0.9 -> ['de_DE','de_CH']
     def formatted_sorted_locales(locales)
       found = weighted_locales(locales).reject(&:empty?).sort_by(&:last).reverse # sort them by weight which is the last entry

spec/fast_gettext/storage_spec.rb

@@ -214,6 +214,32 @@ def thread_safe(method, value_a, value_b)
       FastGettext.locale.should == 'de'
     end
 
+    it "sets a single locale as it would from a header with only that locale" do
+      [nil, ['de_DE', 'en', 'pt']].each do |available|
+        FastGettext.available_locales = available
+        ['en', :en, 'de_DE', :de_DE, 'de-de', 'de_AT', 'pt_BR', 'fr', 'EN', 'zh_Hant', ''].each do |input|
+          from_header = FastGettext.send(:best_locale_in, "#{input},") # not a single locale: parsed
+          FastGettext.send(:best_locale_in, input).should == from_header
+        end
+      end
+    end
+
+    it "does not parse a single locale as a header" do
+      FastGettext.available_locales = ['de', 'en']
+      FastGettext.should_not_receive(:formatted_sorted_locales)
+      FastGettext.locale = :de
+      FastGettext.locale.should == 'de'
+    end
+
+    it "does not hand out the string it was given" do
+      FastGettext.available_locales = nil
+      given = +'en'
+      FastGettext.locale = given
+      FastGettext.locale.should == 'en'
+      FastGettext.locale.should_not equal(given)
+      FastGettext.locale.should_not be_frozen
+    end
+
     it "sets locale from comma seperated" do
       FastGettext.available_locales = ['de_DE','en','xx']
       FastGettext.locale = "de,de-de,en"