don't reuse outdated pull request messages

Prior to a53f0289, hub didn't clean up PULLREQ_EDITMSG files after a successful
pull request. When people upgrade to the new version of hub which reuses PR
messages, these leftover files will get reused when opening new PRs and will
lead to confusion. The hackish solution is to ignore PULLREQ_EDITMSG files that
are older than the hub ruby script on disk.

features/pull_request.feature

@@ -128,6 +128,26 @@ Feature: hub pull-request
     When I successfully run `hub pull-request`
     Then the file ".git/PULLREQ_EDITMSG" should not exist
 
+  Scenario: Ignore outdated PULLREQ_EDITMSG
+    Given the GitHub API server:
+      """
+      post('/repos/mislav/coral/pulls') {
+        assert :title => "Added interactively", :body => nil
+        json :html_url => "https://github.com/mislav/coral/pull/12"
+      }
+      """
+    And a file named ".git/PULLREQ_EDITMSG" with:
+      """
+      Outdated message from old version of hub
+      """
+    Given the file named ".git/PULLREQ_EDITMSG" is older than hub source
+    And the text editor adds:
+      """
+      Added interactively
+      """
+    When I successfully run `hub pull-request`
+    Then the file ".git/PULLREQ_EDITMSG" should not exist
+
   Scenario: Text editor fails
     Given the text editor exits with error status
     And an empty file named ".git/PULLREQ_EDITMSG"

features/steps.rb

@@ -143,6 +143,13 @@ Then /^the file "([^"]*)" should have mode "([^"]*)"$/ do |file, expected_mode|
   end
 end
 
+Given /^the file named "(.+?)" is older than hub source$/ do |file|
+  prep_for_fs_check do
+    time = File.mtime(File.expand_path('../../lib/hub/commands.rb', __FILE__)) - 60
+    File.utime(time, time, file)
+  end
+end
+
 Given /^the remote commit states of "(.*?)" "(.*?)" are:$/ do |proj, ref, json_value|
   if ref == 'HEAD'
     empty_commit

lib/hub/commands.rb

@@ -1017,7 +1017,7 @@ help
     def pullrequest_editmsg(changes)
       message_file = pullrequest_editmsg_file
 
-      if File.exists?(message_file)
+      if valid_editmsg_file?(message_file)
         title, body = read_editmsg(message_file)
         previous_message = [title, body].compact.join("\n\n") if title
       end
@@ -1046,6 +1046,14 @@ help
       [title, body]
     end
 
+    # This unfortunate hack is because older versions of hub never cleaned up
+    # the pullrequest_editmsg_file, which newer hub would pick up and
+    # misinterpret as a message which should be reused after a failed PR.
+    def valid_editmsg_file?(message_file)
+      File.exists?(message_file) &&
+        File.mtime(message_file) > File.mtime(__FILE__)
+    end
+
     def read_msg(message)
       message.split("\n\n", 2).each {|s| s.strip! }.reject {|s| s.empty? }
     end