Add script to update dimensions etc in cr-buildbucket.cfg

For ease of migration from trusty to xenial, I have written simple
script to replace the os dimension.
It also adds mixin to make the builder use builderless bots.

Bug: 954450
Change-Id: Iccce46a96a5ca262523f5b09e6ce308126031c5e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1645532
Commit-Queue: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666633}

infra/scripts/update_dimensions.py

+#!/usr/bin/env python
+# Copyright 2019 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.
+
+# TODO(yyanagisawa): remove this script after the migration. (crbug.com/954450)
+"""
+Script to change bots dimensions from trusty to xenial (crbug.com/954450).
+It also marks the builders to use builderless bots.
+
+How to use:
+  $ ./update_dimensions.py <cr-buildbucket.cfg> <builder name>
+  $ git cl issue 0
+  $ git cl upload
+
+  e.g.
+  $ ./update_dimensions.py cr-buildbucket.cfg android-marshmallow-arm64-rel
+"""
+
+import cStringIO as StringIO
+import os
+import re
+import subprocess
+import sys
+
+
+BUILDERS_PATTERN = re.compile(r'\s*builders\s*{\s*')
+
+
+def InsertMixin(builder_info, mixin_name):
+  """Insert given mixin_name to info.
+
+  Args:
+    builder_info: contents of builder section.
+    mixin_name: mixin name to be inserted.
+  """
+  for line in builder_info.splitlines():
+    if 'mixin' in line:
+      idx = line.find('mixin')
+  builder_info += '%smixins: "%s"\n' % (' ' * idx, mixin_name)
+  return builder_info
+
+
+def UpdateConfig(config_filename, target_builder):
+  """Update cr-buildbucket.cfg to use xenial instead of trusty.
+
+  Args:
+    config_filename: cr-buildbucket.cfg filename.
+    target_builder: target builder name to update.
+  """
+  in_builders = False
+  depth = 0
+  builder_name_line = 'name: "%s"' % target_builder
+  builder_info = ''
+  should_replace = False
+
+  out = StringIO.StringIO()
+
+  with open(config_filename) as f:
+    for line in f:
+      if BUILDERS_PATTERN.match(line) and not '}' in line:
+        in_builders = True
+        depth = 1
+      elif in_builders and '{' in line:
+        depth += 1
+      elif in_builders and '}' in line:
+        depth -= 1
+      if depth == 0:
+        in_builders = False
+        if should_replace:
+          builder_info = InsertMixin(builder_info, 'builderless')
+          out.write(builder_info.replace('Ubuntu-14.04', 'Ubuntu-16.04'))
+        else:
+          out.write(builder_info)
+        builder_info = ''
+        should_replace = False
+      if in_builders:
+        builder_info += line
+      else:
+        out.write(line)
+
+      if in_builders and builder_name_line in line:
+        should_replace = True
+  with open(config_filename, 'w') as f:
+    f.write(out.getvalue())
+
+
+def main(argv):
+  if len(argv) != 3:
+    raise Exception('unexpected args')
+
+  UpdateConfig(argv[1], argv[2])
+  message = """switch trusty to xenial for %s CQ/CI builder
+
+Bug: 954450""" % argv[2]
+  subprocess.check_call(['git', 'add', os.path.basename(argv[1])],
+                        cwd=os.path.dirname(os.path.abspath(argv[1])))
+  subprocess.check_call(
+      ['git', 'commit', '-m', message],
+      cwd=os.path.dirname(os.path.abspath(argv[1])))
+
+if __name__ == '__main__':
+  main(sys.argv)