| // Copyright 2022 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.common.collect.ImmutableSet; |
| import com.google.devtools.build.lib.analysis.config.BuildOptions; |
| import com.google.devtools.build.lib.analysis.config.BuildOptionsView; |
| import com.google.devtools.build.lib.analysis.config.CoreOptions; |
| import com.google.devtools.build.lib.analysis.config.FragmentOptions; |
| import com.google.devtools.build.lib.events.EventHandler; |
| import com.google.devtools.build.lib.skyframe.serialization.autocodec.SerializationConstant; |
| |
| /** |
| * Transitions to a stable, empty configuration for rules that don't rely on configuration. |
| * |
| * <p>This prevents unnecessary configured target forking, which prevents unnecessary build graph |
| * bloat. That in turn reduces build time and memory use. |
| * |
| * <p>For example, imagine {@code cc_library //:foo} in config A depends on config-independent |
| * target {@code //:noconfig} and {@code cc_library //:bar} in config B also depends on {@code |
| * //:noconfig}. Without transitions, {@code //:noconfig} will be configured and analyzed twice: for |
| * configs A and B. This is completely wasteful if {@code //:noconfig} does the same thing |
| * regardless of configuration. Instead, apply this transition to {@code //:noconfig}. |
| * |
| * <p>This is safest for rules that don't produce actions and don't have dependencies. Remember that |
| * even if a rule doesn't read configuration, if any of its transitive dependencies read |
| * configuration or if the rule has a {@code select()}, its output may still be |
| * configuration-dependent. So use with careful discretion. |
| */ |
| public class NoConfigTransition implements PatchTransition { |
| |
| @SerializationConstant public static final NoConfigTransition INSTANCE = new NoConfigTransition(); |
| |
| public static final BuildOptions NO_CONFIG_OPTIONS = BuildOptions.builder().build(); |
| |
| private NoConfigTransition() {} |
| |
| @Override |
| public ImmutableSet<Class<? extends FragmentOptions>> requiresOptionFragments() { |
| return ImmutableSet.of(CoreOptions.class); |
| } |
| |
| @Override |
| public BuildOptions patch(BuildOptionsView options, EventHandler eventHandler) { |
| // Ideally the build options should be empty: no fragment options and no flags. But core Bazel |
| // code assumes CoreOptions exists. For example CoreOptions.check_visibility is required for |
| // basic configured target graph evaluation. So we provide CoreOptions with default values |
| // (not inherited from parent configuration). This means flags like --check_visibility may not |
| // be consistently applied. If this becomes a problem in practice we can carve out exceptions |
| // to flags like that to propagate. |
| // TODO(bazel-team): break out flags that configure Bazel's analysis phase into their own |
| // FragmentOptions and propagate them to this configuration. Those flags should also be |
| // ineligible outputs for other transitions because they're not meant for rule logic. That |
| // would guarantee consistency of flags like --check_visibility while still preventing forking. |
| return BuildOptions.builder() |
| .addFragmentOptions(options.get(CoreOptions.class).getDefault()) |
| .build(); |
| } |
| |
| /** Returns a {@link TransitionFactory} instance that generates the transition. */ |
| public static <T extends TransitionFactory.Data> TransitionFactory<T> createFactory() { |
| return new AutoValue_NoConfigTransition_Factory<>(); |
| } |
| |
| /** A {@link TransitionFactory} implementation that generates the transition. */ |
| @AutoValue |
| abstract static class Factory<T extends TransitionFactory.Data> implements TransitionFactory<T> { |
| @Override |
| public PatchTransition create(T unused) { |
| return INSTANCE; |
| } |
| |
| @Override |
| public boolean isTool() { |
| return true; |
| } |
| } |
| } |