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Introduce NoConfigTransition for rules that don't need configs.
- Provides an alternative for rules that use the host transition as a proxy for nonconfigurable targets. Host transition does that only as a side effect, and isn't the right tool for that purpose - Unblocks host config logic removal - Replace environment()'s host transition NoConfigTransition returns a mostly empty BuildOptions: it has CoreOptions but nothing else. Ideally it'd be completely empty. But too much core Bazel logic reads CoreOptions. We should remove those dependencies. But that's a larger task. See comments in PR diffs for details. This is very similar to NullTransition. This PR doesn't try to merge them because of deep Bazel invariants that NullTransition == source file. Perhaps that can be relaxed. But that's also a larger task. PiperOrigin-RevId: 490598476 Change-Id: Ic4dedc37659d7dc932d7bedc99db17a948566169
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99 changes: 99 additions & 0 deletions
99
...in/java/com/google/devtools/build/lib/analysis/config/transitions/NoConfigTransition.java
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|---|---|---|
| @@ -0,0 +1,99 @@ | ||
| // 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; | ||
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| 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; | ||
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| /** | ||
| * 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 { | ||
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| @SerializationConstant public static final NoConfigTransition INSTANCE = new NoConfigTransition(); | ||
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| private NoConfigTransition() {} | ||
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| @Override | ||
| public ImmutableSet<Class<? extends FragmentOptions>> requiresOptionFragments() { | ||
| return ImmutableSet.of(CoreOptions.class); | ||
| } | ||
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| @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)).build(); | ||
| } | ||
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| /** Returns a {@link TransitionFactory} instance that generates the transition. */ | ||
| public static <T extends TransitionFactory.Data> TransitionFactory<T> createFactory() { | ||
| return new AutoValue_NoConfigTransition_Factory<>(); | ||
| } | ||
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| /** | ||
| * Returns {@code true} if the given {@link TransitionFactory} is an instance of this transition. | ||
| */ | ||
| public static <T extends TransitionFactory.Data> boolean isInstance( | ||
| TransitionFactory<T> instance) { | ||
| return instance instanceof NoConfigTransition.Factory; | ||
| } | ||
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| /** 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; | ||
| } | ||
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| @Override | ||
| public boolean isHost() { | ||
| return true; | ||
| } | ||
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| @Override | ||
| public boolean isTool() { | ||
| return true; | ||
| } | ||
| } | ||
| } |
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