Adding basic find_by_id functionality to Language

lib/linguist/language.rb

@@ -20,10 +20,11 @@ module Linguist
   #
   # Languages are defined in `lib/linguist/languages.yml`.
   class Language
-    @languages       = []
-    @index           = {}
-    @name_index      = {}
-    @alias_index     = {}
+    @languages          = []
+    @index              = {}
+    @name_index         = {}
+    @alias_index        = {}
+    @language_id_index  = {}
 
     @extension_index          = Hash.new { |h,k| h[k] = [] }
     @interpreter_index        = Hash.new { |h,k| h[k] = [] }
@@ -84,6 +85,8 @@ module Linguist
         @filename_index[filename] << language
       end
 
+      @language_id_index[language.language_id] = language
+
       language
     end
 
@@ -193,6 +196,19 @@ module Linguist
       @interpreter_index[interpreter]
     end
 
+    # Public: Look up Languages by its language_id.
+    #
+    # language_id - Integer of language_id
+    #
+    # Examples
+    #
+    #   Language.find_by_id(100)
+    #   # => [#<Language name="Elixir">]
+    #
+    # Returns the matching Language
+    def self.find_by_id(language_id)
+      @language_id_index[language_id.to_i]
+    end
 
     # Public: Look up Language by its name.
     #