PRESUBMIT.py: Add formatting checks.

GN files are checked using the canned presubmit check but we cannot do
the same for C/C++ files: the canned check uses git cl format which can
only use clang-format 5.0 and requires formatting of all the source
code.

Instead we write our own clang-format check, reusing the script that
checks formatting on Travis. To have a recent version of clang-format we
import one from a helper repo.

This also fix a formatting error in .gn and adds licenses to the
clang-format linting scripts.

Change-Id: I4d8208472a8a6bd32ae3ef41c3145abf270a4c37

PRESUBMIT.py

@@ -1,9 +1,69 @@
-# Copyright (c) 2018 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.
+# Copyright 2018 The Dawn Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+import platform
+import subprocess
+
+def _DoClangFormat(input_api, output_api):
+    # Our binary clang-format is a linux binary compiled for x64
+    if platform.system() != 'Linux' or platform.architecture()[0] != '64bit':
+        return [output_api.PresubmitNotifyResult('Skipping clang-format')]
+
+    # We need to know which commit to diff against. It doesn't seem to be exposed anywhere
+    # except in that private member of presubmit_support.Change. This is likely to break
+    # but hopefully we have an updated clang-format in CPID/GS before it does.
+    upstream_commit = input_api.change._upstream
+    if upstream_commit == None:
+        return []
+
+    lint_cmd = [
+        'scripts/lint_clang_format.sh',
+        'third_party/clang-format/clang-format',
+        upstream_commit
+    ]
+
+    # Make clang-format use our linux x64 sysroot because it is compiled with a version of
+    # stdlibc++ that's incompatible with the old libraries present on the bots.
+    env = {
+        'LD_LIBRARY_PATH': os.path.join(
+            os.getcwd(),
+            'build',
+            'linux',
+            'debian_sid_amd64-sysroot',
+            'usr',
+            'lib',
+            'x86_64-linux-gnu'
+        )
+    }
+
+    # Call the linting script and forward the output as a notification or as an error
+    try:
+        output = subprocess.check_output(lint_cmd, env=env);
+        return [output_api.PresubmitNotifyResult(output)]
+    except subprocess.CalledProcessError as e:
+        return [output_api.PresubmitError(e.output)]
+
+def _DoCommonChecks(input_api, output_api):
+    results = []
+    results.extend(input_api.canned_checks.CheckChangedLUCIConfigs(input_api, output_api))
+    results.extend(input_api.canned_checks.CheckGNFormatted(input_api, output_api))
+    results.extend(_DoClangFormat(input_api, output_api))
+    return results
 
 def CheckChangeOnUpload(input_api, output_api):
-    return input_api.canned_checks.CheckChangedLUCIConfigs(input_api, output_api)
+    return _DoCommonChecks(input_api, output_api)
 
 def CheckChangeOnCommit(input_api, output_api):
-    return input_api.canned_checks.CheckChangedLUCIConfigs(input_api, output_api)
+    return _DoCommonChecks(input_api, output_api)