| // Copyright 2018 The Bazel Authors. All rights reserved. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| package com.google.devtools.build.lib.analysis.config.transitions; |
| |
| import com.google.auto.value.AutoValue; |
| import com.google.devtools.build.lib.analysis.config.BuildOptions; |
| import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec; |
| |
| /** A {@link PatchTransition} to a null configuration. */ |
| public class NullTransition implements PatchTransition { |
| |
| @AutoCodec public static final NullTransition INSTANCE = new NullTransition(); |
| |
| private NullTransition() { |
| } |
| |
| @Override |
| public BuildOptions patch(BuildOptions options) { |
| throw new UnsupportedOperationException( |
| "This is only referenced in a few places, so it's easier and more efficient to optimize " |
| + "Blaze's transition logic in the presence of null transitions vs. actually call this " |
| + "method to get results we know ahead of time. If there's ever a need to properly " |
| + "implement this method we can always do so."); |
| } |
| |
| /** Returns a {@link TransitionFactory} instance that generates the null transition. */ |
| public static <T> TransitionFactory<T> createFactory() { |
| return new AutoValue_NullTransition_Factory<>(); |
| } |
| |
| /** |
| * Returns {@code true} if the given {@link TransitionFactory} is an instance of the null |
| * transition. |
| */ |
| public static <T> boolean isInstance(TransitionFactory<T> instance) { |
| return instance instanceof Factory; |
| } |
| |
| /** A {@link TransitionFactory} implementation that generates the null transition. */ |
| @AutoValue |
| abstract static class Factory<T> implements TransitionFactory<T> { |
| @Override |
| public ConfigurationTransition create(T unused) { |
| return INSTANCE; |
| } |
| } |
| } |