Thor should not steal ARGV.

lib/thor.rb

@@ -120,8 +120,8 @@ def method_option(name, options={})
     #   script = MyScript.new(args, options, config)
     #   script.invoke(:task, first_arg, second_arg, third_arg)
     #
-    def start(given_args=ARGV, config={})
-      super do
+    def start(original_args=ARGV, config={})
+      super do |given_args|
         meth = normalize_task_name(given_args.shift)
         task = all_tasks[meth]
 

lib/thor/base.rb

@@ -375,7 +375,7 @@ def namespace(name=nil)
       def start(given_args=ARGV, config={})
         self.debugging = given_args.include?("--debug")
         config[:shell] ||= Thor::Base.shell.new
-        yield
+        yield(given_args.dup)
       rescue Thor::Error => e
         debugging ? (raise e) : config[:shell].error(e.message)
         exit(1) if exit_on_failure?

lib/thor/group.rb

@@ -25,8 +25,8 @@ def desc(description=nil)
     # Start works differently in Thor::Group, it simply invokes all tasks
     # inside the class.
     #
-    def start(given_args=ARGV, config={})
-      super do
+    def start(original_args=ARGV, config={})
+      super do |given_args|
         if Thor::HELP_MAPPINGS.include?(given_args.first)
           help(config[:shell])
           return

spec/base_spec.rb

@@ -233,6 +233,12 @@ def hello
       }.must raise_error(Thor::UndefinedTaskError, 'Could not find task "what" in "my_script" namespace.')
     end
 
+    it "does not steal args" do
+      args = ["foo", "bar", "--force", "true"]
+      MyScript.start(args)
+      args.must == ["foo", "bar", "--force", "true"]
+    end
+
     it "checks unknown options" do
       capture(:stderr) {
         MyScript.start(["foo", "bar", "--force", "true", "--unknown", "baz"])