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.
 """
 
+from __future__ import print_function
+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,
+       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'))
+
+  results = []
+  prebuilt_dartfmt = os.path.join(utils.CheckedInSdkPath(), 'bin', 'dartfmt')

[zra, 2017/03/21 19:51:17]

Please add back the check that bails out if this doesn't exist.

[Jacob, 2017/03/21 20:34:24]

Done.

+
+  for git_file in input_api.AffectedTextFiles():
+    filename = git_file.AbsoluteLocalPath()
+    if filename.endswith('.dart'):
+      cmd = '%s --set-exit-if-changed -n %s ' % (prebuilt_dartfmt, filename)
+      if os.system(cmd):

[zra, 2017/03/21 19:51:17]

I think subprocess tends to be preferred over os.system

[Jacob, 2017/03/21 20:34:24]

Done.

+        old_version_has_errors = False
+        try:
+          old_contents = scm.GIT.Capture(
+            ['show', upstream + ':' + git_file.LocalPath()], cwd=local_root)
+          fd, temp_path = tempfile.mkstemp()
+          f = open(temp_path, 'w')

[zra, 2017/03/21 19:51:17]

with open(temp_path, 'w') as f:
  print(old_contents, file=f)

[Jacob, 2017/03/21 20:34:24]

Done.

+          # Use print to make sure file is terminated with a newline as
+          # git show is losing the trailing newline.
+          print(old_contents, file=f)
+          f.close()
+
+          cmd_old_file = '%s --set-exit-if-changed -n %s ' % (
+            prebuilt_dartfmt, temp_path)
+          if os.system(cmd_old_file):
+            old_version_has_errors = True
+
+          os.close(fd)
+        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:
+          results += [output_api.PresubmitError(
+            'Run\ndartfmt -w %s' % filename)]
+
+  return results
+
 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)