#!/usr/bin/env python3
# Copyright 2020 The Chromium Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Generates extra flags needed to allow temporarily reverting flag expiry.
This program generates three files:
* A C++ source file, containing definitions of base::Features that unexpire
flags that expired in recent milestones, along with a definition of a
definition of a function `flags::ExpiryEnabledForMilestone`
* A C++ header file, containing declarations of those base::Features
* A C++ source fragment, containing definitions of flags_ui::FeatureEntry
structures for flags corresponding to those base::Features
Which milestones are recent is sourced from //chrome/VERSION in the source tree.
"""
import os
import sys
ROOT_PATH = os.path.join(os.path.dirname(__file__), '..', '..')
def get_chromium_version():
"""Parses the chromium version out of //chrome/VERSION."""
with open(os.path.join(ROOT_PATH, 'chrome', 'VERSION')) as f:
for line in f.readlines():
key, value = line.strip().split('=')
if key == 'MAJOR':
return int(value)
return None
def recent_mstones(mstone):
"""Returns the list of milestones considered 'recent' for the given mstone.
Flag unexpiry is available only for flags that expired at recent mstones."""
return [mstone - 1, mstone]
def file_header(prog_name):
"""Returns the header to use on generated files."""
return """// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// This is a generated file. Do not edit it! It was generated by:
// {prog_name}
""".format(prog_name=prog_name)
def gen_features_impl(prog_name, mstone):
"""Generates the definitions for the unexpiry features and the expiry-check
function.
This function generates the contents of a complete C++ source file,
which defines base::Features for unexpiration of flags from recent milestones,
as well as a function ExpiryEnabledForMilestone().
"""
body = file_header(prog_name)
body += """
#include "base/feature_list.h"
#include "chrome/browser/unexpire_flags_gen.h"
namespace flags {
"""
features = [(m, 'UnexpireFlagsM' + str(m)) for m in recent_mstones(mstone)]
for feature in features:
body += f'BASE_FEATURE(k{feature[1]},\n'
body += f' "{feature[1]}",\n'
body += f' base::FEATURE_DISABLED_BY_DEFAULT);\n\n'
body += """// Returns the unexpire feature for the given mstone, if any.
const base::Feature* GetUnexpireFeatureForMilestone(int milestone) {
switch (milestone) {
"""
for feature in features:
body += ' case {m}: return &k{f};\n'.format(m=feature[0], f=feature[1])
body += """ default: return nullptr;
}
}
} // namespace flags
"""
return body
def gen_features_header(prog_name, mstone):
"""Generate a header file declaring features and the expiry predicate.
This header declares the features and function described in
gen_features_impl().
"""
body = file_header(prog_name)
body += """
#ifndef GEN_CHROME_BROWSER_UNEXPIRE_FLAGS_GEN_H_
#define GEN_CHROME_BROWSER_UNEXPIRE_FLAGS_GEN_H_
namespace flags {
"""
for m in recent_mstones(mstone):
body += f'BASE_DECLARE_FEATURE(kUnexpireFlagsM{m});\n'
body += """
// Returns the base::Feature used to decide whether flag expiration is enabled
// for a given milestone, if there is such a feature. If not, returns nullptr.
const base::Feature* GetUnexpireFeatureForMilestone(int milestone);
} // namespace flags
#endif // GEN_CHROME_BROWSER_UNEXPIRE_FLAGS_GEN_H_
"""
return body
def gen_flags_fragment(prog_name, mstone):
"""Generates a .inc file containing flag definitions.
This creates a C++ source fragment defining flags, which are bound to the
features described in gen_features_impl().
"""
# Note: The exact format of the flag name (temporary-unexpire-flags-m{m}) is
# depended on by a hack in UnexpiredMilestonesFromStorage(). See
# https://crbug.com/1101828 for more details.
fragment = """
{{"temporary-unexpire-flags-m{m}",
"Temporarily unexpire M{m} flags.",
"Temporarily unexpire flags that expired as of M{m}. These flags will be"
" removed soon.",
kOsAll | flags_ui::kFlagInfrastructure,
FEATURE_VALUE_TYPE(flags::kUnexpireFlagsM{m})}},
"""
return '\n'.join([fragment.format(m=m) for m in recent_mstones(mstone)])
def update_file_if_stale(filename, data):
"""Writes data to filename if data is different from file's contents on disk.
"""
try:
disk_data = open(filename, 'r').read()
if disk_data == data:
return
except IOError:
pass
open(filename, 'w').write(data)
def main():
mstone = get_chromium_version()
if not mstone:
raise ValueError('Can\'t find or understand //chrome/VERSION')
progname = sys.argv[0]
# Note the mstone - 1 here: the listed expiration mstone is the last mstone in
# which that flag is present, not the first mstone in which it is not present.
update_file_if_stale(sys.argv[1], gen_features_impl(progname, mstone - 1))
update_file_if_stale(sys.argv[2], gen_features_header(progname, mstone - 1))
update_file_if_stale(sys.argv[3], gen_flags_fragment(progname, mstone - 1))
if __name__ == '__main__':
main()
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