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// Copyright 2017 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.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.analysis.config.BuildOptions;
import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
import java.util.List;
import java.util.Objects;
/**
* A configuration transition that composes two other transitions in an ordered sequence.
*
* <p>Example:
*
* <pre>
* transition1: { someSetting = $oldVal + " foo" }
* transition2: { someSetting = $oldVal + " bar" }
* ComposingTransition(transition1, transition2): { someSetting = $oldVal + " foo bar" }
* </pre>
*/
@AutoCodec
public class ComposingTransition implements ConfigurationTransition {
private ConfigurationTransition transition1;
private ConfigurationTransition transition2;
/**
* Creates a {@link ComposingTransition} that applies the sequence: {@code fromOptions ->
* transition1 -> transition2 -> toOptions }.
*/
@AutoCodec.Instantiator
ComposingTransition(ConfigurationTransition transition1, ConfigurationTransition transition2) {
this.transition1 = transition1;
this.transition2 = transition2;
}
@Override
public List<BuildOptions> apply(BuildOptions buildOptions) {
ImmutableList.Builder<BuildOptions> toOptions = ImmutableList.builder();
for (BuildOptions transition1Options : transition1.apply(buildOptions)) {
toOptions.addAll(transition2.apply(transition1Options));
}
return toOptions.build();
}
@Override
public String reasonForOverride() {
return "Basic abstraction for combining other transitions";
}
@Override
public String getName() {
return "(" + transition1.getName() + " + " + transition2.getName() + ")";
}
// Override to allow recursive visiting.
@Override
public <E extends Exception> void visit(Visitor<E> visitor) throws E {
this.transition1.visit(visitor);
this.transition2.visit(visitor);
}
@Override
public int hashCode() {
return Objects.hash(transition1, transition2);
}
@Override
public boolean equals(Object other) {
return other instanceof ComposingTransition
&& ((ComposingTransition) other).transition1.equals(this.transition1)
&& ((ComposingTransition) other).transition2.equals(this.transition2);
}
/**
* Creates a {@link ComposingTransition} that applies the sequence: {@code fromOptions ->
* transition1 -> transition2 -> toOptions }.
*
* <p>Note that this method checks for transitions that cannot be composed, such as if one of the
* transitions is {@link NoTransition} or the host transition, and returns an efficiently composed
* transition.
*/
public static ConfigurationTransition of(
ConfigurationTransition transition1, ConfigurationTransition transition2) {
Preconditions.checkNotNull(transition1);
Preconditions.checkNotNull(transition2);
if (isFinal(transition1)) {
// Since no other transition can be composed with transition1, use it directly.
return transition1;
} else if (transition1 == NoTransition.INSTANCE) {
// Since transition1 causes no changes, use transition2 directly.
return transition2;
}
if (transition2 == NoTransition.INSTANCE) {
// Since transition2 causes no changes, use transition 1 directly.
return transition1;
} else if (isFinal(transition2)) {
// When the second transition is null or a HOST transition, there's no need to compose. But
// this also
// improves performance: host transitions are common, and ConfiguredTargetFunction has special
// optimized logic to handle them. If they were buried in the last segment of a
// ComposingTransition, those optimizations wouldn't trigger.
return transition2;
}
return new ComposingTransition(transition1, transition2);
}
private static boolean isFinal(ConfigurationTransition transition) {
return transition == NullTransition.INSTANCE || transition.isHostTransition();
}
}