1*60517a1eSAndroid Build Coastguard Worker# Copyright 2024 The Bazel Authors. All rights reserved. 2*60517a1eSAndroid Build Coastguard Worker# 3*60517a1eSAndroid Build Coastguard Worker# Licensed under the Apache License, Version 2.0 (the "License"); 4*60517a1eSAndroid Build Coastguard Worker# you may not use this file except in compliance with the License. 5*60517a1eSAndroid Build Coastguard Worker# You may obtain a copy of the License at 6*60517a1eSAndroid Build Coastguard Worker# 7*60517a1eSAndroid Build Coastguard Worker# http://www.apache.org/licenses/LICENSE-2.0 8*60517a1eSAndroid Build Coastguard Worker# 9*60517a1eSAndroid Build Coastguard Worker# Unless required by applicable law or agreed to in writing, software 10*60517a1eSAndroid Build Coastguard Worker# distributed under the License is distributed on an "AS IS" BASIS, 11*60517a1eSAndroid Build Coastguard Worker# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12*60517a1eSAndroid Build Coastguard Worker# See the License for the specific language governing permissions and 13*60517a1eSAndroid Build Coastguard Worker# limitations under the License. 14*60517a1eSAndroid Build Coastguard Worker 15*60517a1eSAndroid Build Coastguard Worker"""A rule to define a target to act as a singleton for label attributes. 16*60517a1eSAndroid Build Coastguard Worker 17*60517a1eSAndroid Build Coastguard WorkerLabel attributes with defaults cannot accept None, otherwise they fall 18*60517a1eSAndroid Build Coastguard Workerback to using the default. A sentinel allows detecting an intended None value. 19*60517a1eSAndroid Build Coastguard Worker""" 20*60517a1eSAndroid Build Coastguard Worker 21*60517a1eSAndroid Build Coastguard WorkerSentinelInfo = provider( 22*60517a1eSAndroid Build Coastguard Worker doc = "Indicates this was the sentinel target.", 23*60517a1eSAndroid Build Coastguard Worker fields = [], 24*60517a1eSAndroid Build Coastguard Worker) 25*60517a1eSAndroid Build Coastguard Worker 26*60517a1eSAndroid Build Coastguard Workerdef _sentinel_impl(ctx): 27*60517a1eSAndroid Build Coastguard Worker _ = ctx # @unused 28*60517a1eSAndroid Build Coastguard Worker return [SentinelInfo()] 29*60517a1eSAndroid Build Coastguard Worker 30*60517a1eSAndroid Build Coastguard Workersentinel = rule(implementation = _sentinel_impl) 31