src/lib/versioning/version-history/cpp/BUILD.gn

# Copyright 2024 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

# Macros to be used as part of the retirement of API levels.
#
# C++ code in non-fuchsia.git repositories that are part of the GN build graph
# (e.g., vendor/*) can reference these to disable code atomically with the
# retirement of these API levels.
#
# Note that these macros are not part of the proper "platform versioning model"
# and must never be exported via the IDK. They should only exist briefly (on
# the order of a few days) for coordinating changes between repositories. See
# https://fxbug.dev/331691736 for more discussion of this technique.
#
# In such situations, follow these steps:
#
# 1. File a bug for the API level retirement process.
# 2. Submit a CL in fuchsia.git that defines a macro like this in this build
#    rule:
#
#    defines = [
#      # TODO(https://fxbug.dev/NNNN): Remove this once N is retired.
#      "FUCHSIA_API_LEVEL_N_STILL_SUPPORTED"
#    ]
#
# 3. Submit a CL in the other repository that removes the functionality as soon
#    as the macro is deleted:
#
#    In the non-fuchsia.git code's BUILD.gn rule, add:
#
#        # TODO(https://fxbug.dev/NNNN): Remove this once N is retired.
#        configs += ["//src/lib/versioning/version-history/cpp:level_retirement_macros"]
#
#    In the C++ code itself add:
#
#        // TODO(https://fxbug.dev/NNNN): Remove this once N is retired.
#        #ifdef FUCHSIA_API_LEVEL_N_STILL_SUPPORTED
#        UseASymbolFromApiLevelN();
#        #endif
#
# 4. Submit a CL in fuchsia.git that removes support for API level N _and_
#    deletes the macro from step (2).
# 5. Submit a CL in the other repository that removes the now-dead code and
#    `config` argument.
# 6. Mark the bug from step (1) as fixed.
config("level_retirement_macros") {
  defines = []
}