Makes GetBuildTime behave identically on all build types.

build/write_build_date_header.py

Index: build/write_build_date_header.py
diff --git a/build/write_build_date_header.py b/build/write_build_date_header.py
new file mode 100755
index 0000000000000000000000000000000000000000..0ba47049b570377c4e090a4c9d1fc7884afb9261
--- /dev/null
+++ b/build/write_build_date_header.py
@@ -0,0 +1,97 @@
+#!/usr/bin/env python
+# Copyright (c) 2016 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.
+"""Writes a file that contains a define that approximates the build date.
+
+For unofficial builds, the build date is set to the most recent first Sunday
+of a month, in UTC time.
+
+For official builds, the build date is set to the current date (in UTC).
+
+It is also possible to explicitly set a build date to be used.
+
+The reason for using the first Sunday of a month for unofficial builds is that
+it is a time where invalidating the build cache shouldn't have major
+reprecussions (due to lower load).
+"""
+
+import argparse
+import calendar
+import datetime
+import os
+import sys
+
+
+def GetFirstSundayOfMonth(year, month):
+  """Returns the first sunday of the given month of the given year."""
+  weeks = calendar.Calendar().monthdays2calendar(year, month)
+  # Return the first day in the first week that is a Sunday.
+  return [date_day[0] for date_day in weeks[0] if date_day[1] == 6][0]
+
+
+# Validate that GetFirstSundayOfMonth works.
+assert GetFirstSundayOfMonth(2016, 2) == 7
+assert GetFirstSundayOfMonth(2016, 3) == 6
+assert GetFirstSundayOfMonth(2000, 1) == 2
+
+
+def GetBuildDate(build_type, utc_now):
+  """Gets the approximate build date given the specific build type."""
+  day = utc_now.day
+  month = utc_now.month
+  year = utc_now.year
+  if build_type != 'official':
+    first_sunday = GetFirstSundayOfMonth(year, month)
+    # If our build is after the first Sunday, we've already refreshed our build
+    # cache on a quiet day, so just use that day.
+    # Otherwise, take the first Sunday of the previous month.
+    if day >= first_sunday:
+      day = first_sunday
+    else:
+      month -= 1
+      if month == 0:
+        month = 12
+        year -= 1
+      day = GetFirstSundayOfMonth(year, month)
+  return '{:%b %d %Y}'.format(datetime.date(year, month, day))
+
+
+# Validate that GetBuildDate works.
+assert GetBuildDate('default', datetime.date(2016, 2, 6)) == 'Jan 03 2016'
+assert GetBuildDate('default', datetime.date(2016, 2, 7)) == 'Feb 07 2016'
+assert GetBuildDate('default', datetime.date(2016, 2, 8)) == 'Feb 07 2016'
+
+
+def main():
+  argument_parser = argparse.ArgumentParser()
+  argument_parser.add_argument('output_file', help='The file to write to')
+  argument_parser.add_argument('build_type', help='The type of build',
+                               choices=('official', 'default'))
+  argument_parser.add_argument('build_date_override', nargs='?',
+                               help='Optional override for the build date')
+  args = argument_parser.parse_args()
+
+  if args.build_date_override:
+    build_date = args.build_date_override
+  else:
+    build_date = GetBuildDate(args.build_type, datetime.datetime.utcnow())
+
+  output = ('// Generated by //build/write_build_date_header.py\n'
+           '#ifndef BUILD_DATE\n'
+           '#define BUILD_DATE "{}"\n'
+           '#endif // BUILD_DATE\n'.format(build_date))
+
+  current_contents = ''
+  if os.path.isfile(args.output_file):
+    with open(args.output_file, 'r') as current_file:
+      current_contents = current_file.read()
+
+  if current_contents != output:
+    with open(args.output_file, 'w') as output_file:
+      output_file.write(output)
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main())