git-squash-branch: handle empty squashes and dirty trees

git_common.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Monkeypatch IMapIterator so that Ctrl-C can kill everything properly.
 # Derived from https://gist.github.com/aljungberg/626518
 import multiprocessing.pool
 from multiprocessing.pool import IMapIterator
 def wrapper(func):
   def wrap(self, timeout=None):
@@ skipping 584 matching lines @@
 
 
 def set_branch_config(branch, option, value, scope='local'):
   set_config('branch.%s.%s' % (branch, option), value, scope=scope)
 
 
 def set_config(option, value, scope='local'):
   run('config', '--' + scope, option, value)
 
 
+def get_dirty_files():
+  # Make sure index is up-to-date before running diff-index.
+  run_with_retcode('update-index', '--refresh', '-q')
+  return run('diff-index', '--name-status', 'HEAD')
+
+
+def is_dirty_git_tree(cmd):
+  dirty = get_dirty_files()
+  if dirty:
+    print 'Cannot %s with a dirty tree. You must commit locally first.' % cmd
+    print 'Uncommitted files: (git diff-index --name-status HEAD)'
+    print dirty[:4096]
+    if len(dirty) > 4096: # pragma: no cover
+      print '... (run "git diff-index --name-status HEAD" to see full output).'
+    return True
+  return False
+
+
 def squash_current_branch(header=None, merge_base=None):
   header = header or 'git squash commit.'
   merge_base = merge_base or get_or_create_merge_base(current_branch())
   log_msg = header + '\n'
   if log_msg:
     log_msg += '\n'
   log_msg += run('log', '--reverse', '--format=%H%n%B', '%s..HEAD' % merge_base)
   run('reset', '--soft', merge_base)
+
+  if not get_dirty_files():
+    # Sometimes the squash can result in the same tree, meaning that there is
+    # nothing to commit at this point.
+    print 'Nothing to commit; squashed branch is empty'
+    return False
   run('commit', '-a', '-F', '-', indata=log_msg)
+  return True
 
 
 def tags(*args):
   return run('tag', *args).splitlines()
 
 
 def thaw():
   took_action = False
   for sha in (s.strip() for s in run_stream('rev-list', 'HEAD').xreadlines()):
     msg = run('show', '--format=%f%b', '-s', 'HEAD')
@@ skipping 138 matching lines @@
         hash=branch_hash, upstream=upstream_branch, ahead=ahead, behind=behind)
 
   # Set None for upstreams which are not branches (e.g empty upstream, remotes
   # and deleted upstream branches).
   missing_upstreams = {}
   for info in info_map.values():
     if info.upstream not in info_map and info.upstream not in missing_upstreams:
       missing_upstreams[info.upstream] = None
 
   return dict(info_map.items() + missing_upstreams.items())