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'))
+
+  prebuilt_dartfmt = os.path.join(utils.CheckedInSdkPath(), 'bin', 'dartfmt')
+
+  if not os.path.isfile(prebuilt_dartfmt):
+    print('WARNING: dartfmt not found: %s' % (prebuilt_dartfmt))
+    return []
+
+  def HasFormatErrors(filename):
+    try:
+      subprocess.check_output(
+        [prebuilt_dartfmt, '--set-exit-if-changed', '-n', filename])
+    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):
+        old_version_has_errors = False
+        try:
+          old_contents = scm.GIT.Capture(
+            ['show', upstream + ':' + git_file.LocalPath()], cwd=local_root)
+          fd, temp_path = tempfile.mkstemp()
+          # Use print to make sure file is terminated with a newline as
+          # "git show" is losing the trailing newline.
+          with open(temp_path, 'w') as f:
+            print(old_contents, file=f)
+
+          if HasFormatErrors(temp_path):
+            old_version_has_errors = True
+
+          os.close(fd)

[zra, 2017/03/21 20:47:49]

It might also be a good idea to manually delete the file. The docs seem to
indicate that one should:
https://docs.python.org/2/library/tempfile.html#tempfile.mkstemp

Maybe it would be better to use tempfile.NamedTemporaryFile like:

with tempfile.NamedTemporaryFile() as temp:
  print(old_contents, file=temp)
  if HasFormatErrors(temp.name):
    ...

Also be sure to check that this all works on Windows before landing. Sometimes
stuff like this works differently there.

[Jacob, 2017/03/21 22:04:21]

Worked around a bug in how the formatter handles reading content from stdin so
switched to executing the formatter using stdin which eliminates the need for a
tmp file

+        except subprocess.CalledProcessError as e:

[zra, 2017/03/21 20:47:49]

Can this still happen? It looks like HasFormatErrors is catching
CalledProcessError.

[Jacob, 2017/03/21 22:04:22]

scm.GIT.Capture is throwing this error. 

+          # 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)