Allow to merge with --ff-only option

features/merge.feature

@@ -27,6 +27,27 @@ Feature: hub merge
       Add `hub merge` command
       """
 
+  Scenario: Merge pull request with --ff-only option
+    Given the GitHub API server:
+      """
+      require 'json'
+      get('/repos/defunkt/hub/pulls/164') { json \
+        :head => {
+          :label => 'jfirebaugh:hub_merge',
+          :repo  => {:private => false}
+        },
+        :title => "Add `hub merge` command"
+      }
+      """
+    And there is a commit named "jfirebaugh/hub_merge"
+    When I successfully run `hub merge --ff-only https://github.com/defunkt/hub/pull/164`
+    Then "git fetch git://github.com/jfirebaugh/hub.git +refs/heads/hub_merge:refs/remotes/jfirebaugh/hub_merge" should be run
+    When I successfully run `git show -s --format=%B`
+    Then the output should contain:
+      """
+      Fast-forward (no commit created; -m option ignored)
+      """
+
   Scenario: Merge private pull request
     Given the GitHub API server:
       """

lib/hub/commands.rb

@@ -443,8 +443,9 @@ module Hub
 
         idx = args.index url_arg
         args.delete_at idx
-        args.insert idx, merge_head, '--no-ff', '-m',
-                    "Merge pull request ##{pull_id} from #{merge_head}\n\n#{pull_data['title']}"
+        args.insert idx, merge_head, '-m', "Merge pull request ##{pull_id} from #{merge_head}\n\n#{pull_data['title']}"
+        idx = args.index '-m'
+        args.insert idx, '--no-ff' unless args.include?('--ff-only')
       end
     end