friendly error for `pull-request` in detached HEAD

features/pull_request.feature

@@ -3,6 +3,13 @@ Feature: hub pull-request
     Given I am in "dotfiles" git repo
     And I am "mislav" on github.com with OAuth token "OTOKEN"
 
+  Scenario: Detached HEAD
+    Given the "origin" remote has url "git://github.com/mislav/coral.git"
+    And I am in detached HEAD
+    When I run `hub pull-request`
+    Then the stderr should contain "Aborted: not currently on any branch.\n"
+    And the exit status should be 1
+
   Scenario: Non-GitHub repo
     Given the "origin" remote has url "mygh:Manganeez/repo.git"
     When I run `hub pull-request`

features/steps.rb

@@ -69,6 +69,12 @@ Given /^I am on the "([^"]+)" branch(?: with upstream "([^"]+)")?$/ do |name, up
   run_silent %(git checkout --quiet -B #{name} --track #{upstream})
 end
 
+Given /^I am in detached HEAD$/ do
+  empty_commit
+  empty_commit
+  run_silent %(git checkout HEAD^)
+end
+
 Given /^the current dir is not a repo$/ do
   in_current_dir do
     FileUtils.rm_rf '.git'

lib/hub/commands.rb

@@ -81,6 +81,10 @@ module Hub
       base_project = local_repo.main_project
       head_project = local_repo.current_project
 
+      unless current_branch
+        abort "Aborted: not currently on any branch."
+      end
+
       unless base_project
         abort "Aborted: the origin remote doesn't point to a GitHub repository."
       end