Add presubmit check that runs dartfmt

PRESUBMIT.py

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 """Top-level presubmit script for Dart.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
 
+import imp
+import os
+import scm
+import subprocess
+import tempfile
+
+def _CheckBuildStatus(input_api, output_api):
+   results = []
+   status_check = input_api.canned_checks.CheckTreeIsOpen(
+       input_api,
+       output_api,
+       json_url='http://dart-status.appspot.com/current?format=json')
+   results.extend(status_check)
+   return results
+
+def _CheckDartFormat(input_api, output_api):
+  local_root = input_api.change.RepositoryRoot()
+  upstream = input_api.change._upstream
+  utils = imp.load_source('utils',
+      os.path.join(local_root, 'tools', 'utils.py'))
+
+  prebuilt_dartfmt = os.path.join(utils.CheckedInSdkPath(), 'bin', 'dartfmt')
+
+  windows = utils.GuessOS() == 'win32'
+  if windows:
+    prebuilt_dartfmt += '.bat'
+
+  if not os.path.isfile(prebuilt_dartfmt):
+    print('WARNING: dartfmt not found: %s' % (prebuilt_dartfmt))
+    return []
+
+  def HasFormatErrors(filename=None, contents=None):
+    args = [prebuilt_dartfmt, '--set-exit-if-changed']
+    if contents:
+      process = subprocess.Popen(args,
+                                 stdout=subprocess.PIPE,
+                                 stdin=subprocess.PIPE
+                                 )
+      out, err = process.communicate(input=contents)
+
+      # There was a bug in the return code dartfmt returns when reading from
+      # stdin so we have to check whether the content matches rather than using
+      # the return code. When the next version of the dartfmt lands in the sdk
+      # we can switch this line to "return process.returncode != 0"
+      return out != contents
+    else:
+      try:
+        subprocess.check_output(args + [filename, '-n'])
+      except subprocess.CalledProcessError:
+        return True
+      return False
+
+  unformatted_files = []
+  for git_file in input_api.AffectedTextFiles():
+    filename = git_file.AbsoluteLocalPath()
+    if filename.endswith('.dart'):
+      if HasFormatErrors(filename=filename):
+        old_version_has_errors = False
+        try:
+          path = git_file.LocalPath()
+          if windows:
+            # Git expects a linux style path.
+            path = path.replace(os.sep, '/')
+          old_contents = scm.GIT.Capture(
+            ['show', upstream + ':' + path],
+            cwd=local_root,
+            strip_out=False)
+          if HasFormatErrors(contents=old_contents):
+            old_version_has_errors = True
+        except subprocess.CalledProcessError as e:
+          # TODO(jacobr): verify that the error really is that the file was
+          # added for this CL.
+          old_version_has_errors = False
+
+        if old_version_has_errors:
+          print("WARNING: %s has existing and possibly new dartfmt issues" %
+            git_file.LocalPath())
+        else:
+          unformatted_files.append(filename)
+
+  if unformatted_files:
+    return [output_api.PresubmitError(
+        'File output does not match dartfmt.\n'
+        'Fix these issues with:\n'
+        'dartfmt -w \\\n%s' % ' \\\n'.join(unformatted_files))]
+
+  return []
+
 def CheckChangeOnCommit(input_api, output_api):
-  results = []
-  status_check = input_api.canned_checks.CheckTreeIsOpen(
-      input_api,
-      output_api,
-      json_url='http://dart-status.appspot.com/current?format=json')
-  results.extend(status_check)
-  return results
+  return (_CheckBuildStatus(input_api, output_api) +
+          _CheckDartFormat(input_api, output_api))
+
+def CheckChangeOnUpload(input_api, output_api):
+  return _CheckDartFormat(input_api, output_api)