Fix 'git cl format'

git_cl.py

Index: git_cl.py
diff --git a/git_cl.py b/git_cl.py
index b34edcf38df385ee4be9566372e16259c696c6d4..29c38f93fdd54a63b46b4ea8f0b7956ec4c929bc 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -1952,24 +1952,44 @@ def CMDformat(parser, args):
   if args:
     parser.error('Unrecognized args: %s' % ' '.join(args))
 
+  # Generate diff for the current branch's changes.
+  diff_cmd = ['diff', '--no-ext-diff']
   if opts.full:
-    cmd = ['diff', '--name-only', '--'] + ['.*' + ext for ext in CLANG_EXTS]
-    files = RunGit(cmd).split()
+    # Only list the names of modified files.
+    diff_cmd.append('--name-only')
+  else:
+    # Only generate context-less patches.
+    diff_cmd.append('-U0')
+
+  # Grab the merge-base commit, i.e. the upstream commit of the current
+  # branch when it was created or the last time it was rebased. This is
+  # to cover the case where the user may have called "git fetch origin",
+  # moving the origin branch to a newer commit, but hasn't rebased yet.
+  cl = Changelist()
+  upstream_commit = RunGit(['merge-base', 'HEAD', cl.GetUpstreamBranch()])

[M-A Ruel, 2013/05/17 14:13:59]

Note that  cl.GetUpstreamBranch() could return nothing or upstream_commit could
be empty. In either case, just print an error message to explain the situation
and exit. With the current code, it'd diff against the last commit, which may be
unexpected.

[digit1, 2013/05/17 15:00:03]

I see, I've updated the code to do that. Thanks, though I don't have a good way
to test the new code path, hum...

+  diff_cmd.append(upstream_commit.strip())
+
+  # Handle source file filtering.
+  diff_cmd.append('--')
+  diff_cmd += ['*' + ext for ext in CLANG_EXTS]
+  diff_output = RunGit(diff_cmd)
+
+  if opts.full:
+    # diff_output is a list of files to send to clang-format.
+    files = diff_output.split()

[M-A Ruel, 2013/05/17 14:13:59]

I'd prefer splitlines() so you don't break files with whitespace in them. In
practice we don't support these but still.

[digit1, 2013/05/17 15:00:03]

Done.

     if not files:
       print "Nothing to format."
       return 0
-    RunCommand(['clang-format', '-i'] + files)
+    RunCommand(['clang-format', '-i', '-style', 'Chromium'] + files)
   else:
+    # diff_output is a patch to send to clang-format-diff.py
     cfd_path = os.path.join('/usr', 'lib', 'clang-format',
                             'clang-format-diff.py')
     if not os.path.exists(cfd_path):
       print >> sys.stderr, 'Could not find clang-format-diff at %s.' % cfd_path
       return 2
-    cmd = ['diff', '-U0', '@{u}', '--'] + ['.*' + ext for ext in CLANG_EXTS]
-    diff = RunGit(cmd)
-    cmd = [sys.executable, '/usr/lib/clang-format/clang-format-diff.py',
-           '-style', 'Chromium']
-    RunCommand(cmd, stdin=diff)
+    cmd = [sys.executable, cfd_path, '-style', 'Chromium']
+    RunCommand(cmd, stdin=diff_output)
 
   return 0