improve `checkout` command

Now forwards flags to internal `checkout` command, resets the existing
local branch by default.

Closes #132

README.md

@@ -201,7 +201,7 @@ superpowers:
 
     # $ git checkout https://github.com/defunkt/hub/pull/73
     # > git remote add -f -t feature git://github:com/mislav/hub.git
-    # > git checkout -b mislav-feature mislav/feature
+    # > git checkout --track -B mislav-feature mislav/feature
 
     # $ git checkout https://github.com/defunkt/hub/pull/73 custom-branch-name
 

lib/hub/commands.rb

@@ -303,17 +303,20 @@ module Hub
 
     # $ git checkout https://github.com/defunkt/hub/pull/73
     # > git remote add -f -t feature git://github:com/mislav/hub.git
-    # > git checkout -b mislav-feature mislav/feature
+    # > git checkout --track -B mislav-feature mislav/feature
     def checkout(args)
-      if (2..3) === args.length and url = resolve_github_url(args[1]) and url.project_path =~ /^pull\/(\d+)/
+      _, url_arg, new_branch_name = args.words
+      if url = resolve_github_url(url_arg) and url.project_path =~ /^pull\/(\d+)/
         pull_id = $1
 
         load_net_http
         response = http_request(url.project.api_pullrequest_url(pull_id, 'json'))
         pull_data = JSON.parse(response.body)['pull']
 
+        args.delete new_branch_name
         user, branch = pull_data['head']['label'].split(':', 2)
-        new_branch_name = args[2] || "#{user}-#{branch}"
+        abort "Error: #{user}'s fork is not available anymore" unless pull_data['head']['repository']
+        new_branch_name ||= "#{user}-#{branch}"
 
         if remotes.include? user
           args.before ['remote', 'set-branches', '--add', user, branch]
@@ -323,7 +326,9 @@ module Hub
                                                                :https => https_protocol?)
           args.before ['remote', 'add', '-f', '-t', branch, user, url]
         end
-        args[1..-1] = ['-b', new_branch_name, "#{user}/#{branch}"]
+        idx = args.index url_arg
+        args.delete_at idx
+        args.insert idx, '--track', '-B', new_branch_name, "#{user}/#{branch}"
       end
     end
 

test/hub_test.rb

@@ -947,8 +947,8 @@ class HubTest < Test::Unit::TestCase
       to_return(:body => mock_pull_response('blueyed:feature'))
 
     assert_commands 'git remote add -f -t feature blueyed git://github.com/blueyed/hub.git',
-      'git checkout -b blueyed-feature blueyed/feature',
-      "checkout https://github.com/defunkt/hub/pull/73/files"
+      'git checkout -f --track -B blueyed-feature blueyed/feature -q',
+      "checkout -f https://github.com/defunkt/hub/pull/73/files -q"
   end
 
   def test_checkout_private_pullrequest
@@ -956,7 +956,7 @@ class HubTest < Test::Unit::TestCase
       to_return(:body => mock_pull_response('blueyed:feature', :private))
 
     assert_commands 'git remote add -f -t feature blueyed git@github.com:blueyed/hub.git',
-      'git checkout -b blueyed-feature blueyed/feature',
+      'git checkout --track -B blueyed-feature blueyed/feature',
       "checkout https://github.com/defunkt/hub/pull/73/files"
   end
 
@@ -965,7 +965,7 @@ class HubTest < Test::Unit::TestCase
       to_return(:body => mock_pull_response('blueyed:feature'))
 
     assert_commands 'git remote add -f -t feature blueyed git://github.com/blueyed/hub.git',
-      'git checkout -b review blueyed/feature',
+      'git checkout --track -B review blueyed/feature',
       "checkout https://github.com/defunkt/hub/pull/73/files review"
   end
 
@@ -977,7 +977,7 @@ class HubTest < Test::Unit::TestCase
 
     assert_commands 'git remote set-branches --add blueyed feature',
       'git fetch blueyed +refs/heads/feature:refs/remotes/blueyed/feature',
-      'git checkout -b blueyed-feature blueyed/feature',
+      'git checkout --track -B blueyed-feature blueyed/feature',
       "checkout https://github.com/defunkt/hub/pull/73/files"
   end