Add find lexer by mimetype

lib/linguist/lexer.rb

@@ -9,9 +9,10 @@ module Linguist
   # filenames - Filename globs (*.js)
   # mimetypes - Mime types (application/javascript)
   class Lexer < Struct.new(:name, :aliases, :filenames, :mimetypes)
-    @lexers      = []
+    @lexers          = []
-    @name_index  = {}
+    @name_index      = {}
-    @alias_index = {}
+    @alias_index     = {}
+    @mimetypes_index = {}
 
     # Internal: Test if system has Pygments
     #
@@ -58,6 +59,20 @@ module Linguist
       @alias_index[name]
     end
 
+    # Public: Look up Lexer by one of it's mime types.
+    #
+    # type - A mime type String.
+    #
+    # Examples
+    #
+    #  Lexer.find_by_mimetype('application/x-ruby')
+    #  # => #<Lexer name="Ruby">
+    #
+    # Returns the Lexer or nil if none was found.
+    def self.find_by_mimetype(type)
+      @mimetypes_index[type]
+    end
+
     # Public: Look up Lexer by name or alias.
     #
     # name - A case-insensitive String name or alias
@@ -132,6 +147,15 @@ module Linguist
 
         @alias_index[name] = lexer
       end
+
+      lexer.mimetypes.each do |type|
+        # All Lexer mimetypes should be unique. Warn if there is a duplicate.
+        if @mimetypes_index.key?(name)
+          warn "Duplicate mimetype: #{name}"
+        end
+
+        @mimetypes_index[type] = lexer
+      end
     end
   end
 end

test/test_lexer.rb

@@ -32,6 +32,19 @@ class TestLexer < Test::Unit::TestCase
     end
   end
 
+  def test_find_by_mimetype
+    assert_equal Lexer['Ruby'], Lexer.find_by_mimetype('text/x-ruby')
+    assert_equal Lexer['Ruby'], Lexer.find_by_mimetype('application/x-ruby')
+  end
+
+  def test_find_all_by_mimetype
+    Lexer.all.each do |lexer|
+      lexer.mimetypes.each do |type|
+        assert_equal lexer, Lexer.find_by_mimetype(type)
+      end
+    end
+  end
+
   def test_name
     assert_equal 'Ruby',   Lexer['Ruby'].name
     assert_equal 'Python', Lexer['Python'].name