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- #!/usr/bin/env python
- # Copyright 2020 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.
- """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. All rights reserved.
- // 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 += 'const base::Feature k{f} {{\n'.format(f=feature[1])
- body += ' "{f}",\n'.format(f=feature[1])
- body += ' base::FEATURE_DISABLED_BY_DEFAULT\n'
- body += '};\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 += 'extern const base::Feature kUnexpireFlagsM{m};\n'.format(m=m)
- 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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