language interpreters and shebang lines

Add an interpreter array to each language, and match interpreters found
in the shebang lines of scripts to this array to identify the language
of scripts.

With suggestions from tnm. https://github.com/github/linguist/pull/687

lib/linguist/language.rb

@@ -17,6 +17,7 @@ module Linguist
     @alias_index     = {}
 
     @extension_index          = Hash.new { |h,k| h[k] = [] }
+    @interpreter_index        = Hash.new { |h,k| h[k] = [] }
     @filename_index           = Hash.new { |h,k| h[k] = [] }
     @primary_extension_index  = {}
 
@@ -71,6 +72,10 @@ module Linguist
 
       @primary_extension_index[language.primary_extension] = language
 
+      language.interpreters.each do |interpreter|
+        @interpreter_index[interpreter] << language
+      end
+
       language.filenames.each do |filename|
         @filename_index[filename] << language
       end
@@ -101,6 +106,8 @@ module Linguist
         data = data.call() if data.respond_to?(:call)
         if data.nil? || data == ""
           nil
+        elsif result = find_by_shebang(data)
+          result.first
         elsif result = Classifier.classify(Samples::DATA, data, possible_languages.map(&:name)).first
           Language[result[0]]
         end
@@ -162,6 +169,20 @@ module Linguist
       langs.compact.uniq
     end
 
+    # Public: Look up Languages by shebang line.
+    #
+    # data - Array of tokens or String data to analyze.
+    #
+    # Examples
+    #
+    #   Language.find_by_shebang("#!/bin/bash\ndate;")
+    #   # => [#<Language name="Bash">]
+    #
+    # Returns the matching Language
+    def self.find_by_shebang(data)
+      @interpreter_index[Linguist.interpreter_from_shebang(data)]
+    end
+
     # Public: Look up Language by its name or lexer.
     #
     # name - The String name of the Language
@@ -247,6 +268,7 @@ module Linguist
 
       # Set extensions or default to [].
       @extensions = attributes[:extensions] || []
+      @interpreters = attributes[:interpreters]   || []
       @filenames  = attributes[:filenames]  || []
 
       unless @primary_extension = attributes[:primary_extension]
@@ -359,6 +381,15 @@ module Linguist
     # Returns the extension String.
     attr_reader :primary_extension
 
+    # Public: Get interpreters
+    #
+    # Examples
+    #
+    #   # => ['awk', 'gawk', 'mawk' ...]
+    #
+    # Returns the interpreters Array
+    attr_reader :interpreters
+
     # Public: Get filenames
     #
     # Examples
@@ -452,11 +483,13 @@ module Linguist
   end
 
   extensions = Samples::DATA['extnames']
+  interpreters = Samples::DATA['interpreters']
   filenames = Samples::DATA['filenames']
   popular = YAML.load_file(File.expand_path("../popular.yml", __FILE__))
 
   YAML.load_file(File.expand_path("../languages.yml", __FILE__)).each do |name, options|
     options['extensions'] ||= []
+    options['interpreters'] ||= []
     options['filenames'] ||= []
 
     if extnames = extensions[name]
@@ -467,6 +500,18 @@ module Linguist
       end
     end
 
+    if interpreters == nil
+      interpreters = {}
+    end
+
+    if interpreter_names = interpreters[name]
+      interpreter_names.each do |interpreter|
+        if !options['interpreters'].include?(interpreter)
+          options['interpreters'] << interpreter
+        end
+      end
+    end
+
     if fns = filenames[name]
       fns.each do |filename|
         if !options['filenames'].include?(filename)
@@ -487,6 +532,7 @@ module Linguist
       :searchable        => options.key?('searchable') ? options['searchable'] : true,
       :search_term       => options['search_term'],
       :extensions        => options['extensions'].sort,
+      :interpreters      => options['interpreters'].sort,
       :primary_extension => options['primary_extension'],
       :filenames         => options['filenames'],
       :popular           => popular.include?(name)