Add -C/--directory option the same as GNU make

lib/rake/application.rb

@@ -433,6 +433,13 @@ def standard_rake_options # :nodoc:
               select_tasks_to_show(options, :describe, value)
             }
           ],
+          ["--directory", "-C [DIRECTORY]",
+            "Change to DIRECTORY before doing anything.",
+            lambda { |value|
+              Dir.chdir value
+              @original_dir = Dir.pwd
+            }
+          ],
           ["--dry-run", "-n",
             "Do a dry run without executing actions.",
             lambda { |value|

test/test_rake_application_options.rb

@@ -65,6 +65,28 @@ def test_describe_with_pattern
     end
   end
 
+  def test_directory
+    pwd = Dir.pwd
+    [["--directory"], "--directory=", ["-C"], "-C"].each do |flag|
+      Dir.mktmpdir do |dir|
+        begin
+          flags(flag.dup << dir) do
+            assert_equal(File.realpath(dir), @app.original_dir)
+          end
+        ensure
+          Dir.chdir(pwd)
+        end
+        begin
+          assert_raises(Errno::ENOENT) do
+            flags(flag.dup << dir+"/nonexistent")
+          end
+        ensure
+          Dir.chdir(pwd)
+        end
+      end
+    end
+  end
+
   def test_execute
     $xyzzy = 0
     flags("--execute=$xyzzy=1", "-e $xyzzy=1") do