Use filenames as a definitive answer (#2006)

* Separate find_by_extension and find_by_filename
find_by_extension now takes a path as argument and not only the file extension.
Currently only find_by_extension is used as a strategy.

* Add find_by_filename as first strategy

lib/linguist/language.rb

@@ -11,6 +11,7 @@ require 'linguist/samples'
 require 'linguist/file_blob'
 require 'linguist/blob_helper'
 require 'linguist/strategy/filename'
+require 'linguist/strategy/extension'
 require 'linguist/strategy/modeline'
 require 'linguist/shebang'
 
@@ -129,41 +130,46 @@ module Linguist
 
     # Public: Look up Languages by filename.
     #
+    # The behaviour of this method recently changed.
+    # See the second example below.
+    #
     # filename - The path String.
     #
     # Examples
     #
+    #   Language.find_by_filename('Cakefile')
+    #   # => [#<Language name="CoffeeScript">]
     #   Language.find_by_filename('foo.rb')
-    #   # => [#<Language name="Ruby">]
+    #   # => []
     #
     # Returns all matching Languages or [] if none were found.
     def self.find_by_filename(filename)
       basename = File.basename(filename)
-
-      # find the first extension with language definitions
-      extname = FileBlob.new(filename).extensions.detect do |e|
-        !@extension_index[e].empty?
-      end
-
-      (@filename_index[basename] + @extension_index[extname]).compact.uniq
+      @filename_index[basename]
     end
 
     # Public: Look up Languages by file extension.
     #
-    # extname - The extension String.
+    # The behaviour of this method recently changed.
+    # See the second example below.
+    #
+    # filename - The path String.
     #
     # Examples
     #
-    #   Language.find_by_extension('.rb')
+    #   Language.find_by_extension('dummy.rb')
     #   # => [#<Language name="Ruby">]
-    #
     #   Language.find_by_extension('rb')
-    #   # => [#<Language name="Ruby">]
+    #   # => []
     #
     # Returns all matching Languages or [] if none were found.
-    def self.find_by_extension(extname)
-      extname = ".#{extname}" unless extname.start_with?(".")
-      @extension_index[extname.downcase]
+    def self.find_by_extension(filename)
+      # find the first extension with language definitions
+      extname = FileBlob.new(filename.downcase).extensions.detect do |e|
+        !@extension_index[e].empty?
+      end
+
+      @extension_index[extname]
     end
 
     # Public: Look up Languages by interpreter.

lib/linguist/strategy/extension.rb

@@ -0,0 +1,10 @@
+module Linguist
+  module Strategy
+    # Detects language based on extension
+    class Extension
+      def self.call(blob, _)
+        Language.find_by_extension(blob.name.to_s)
+      end
+    end
+  end
+end

lib/linguist/strategy/filename.rb

@@ -1,9 +1,10 @@
 module Linguist
   module Strategy
-    # Detects language based on filename and/or extension
+    # Detects language based on filename
     class Filename
       def self.call(blob, _)
-        Language.find_by_filename(blob.name.to_s)
+        name = blob.name.to_s
+        Language.find_by_filename(name)
       end
     end
   end