gradle-master/subprojects/execution/src/main/java/org/gradle/internal/execution/steps/StoreExecutionStateStep.java
/*
 * Copyright 2018 the original author or authors.
 *
 * 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 org.gradle.internal.execution.steps;

import com.google.common.collect.ImmutableSortedMap;
import org.gradle.internal.execution.UnitOfWork;
import org.gradle.internal.execution.history.changes.ChangeDetectorVisitor;
import org.gradle.internal.execution.history.changes.OutputFileChanges;
import org.gradle.internal.snapshot.FileSystemSnapshot;

public class StoreExecutionStateStep<C extends PreviousExecutionContext, R extends AfterExecutionResult> implements Step<C, R> {
    private final Step<? super C, ? extends R> delegate;

    public StoreExecutionStateStep(
        Step<? super C, ? extends R> delegate
    ) {
        this.delegate = delegate;
    }

    @Override
    public R execute(UnitOfWork work, C context) {
        R result = delegate.execute(work, context);
        context.getHistory()
            .ifPresent(history -> result.getAfterExecutionState()
                .ifPresent(
                    afterExecutionState -> {
                        // We do not store the history if there was a failure and the outputs did not change, since then the next execution can be incremental.
                        // For example the current execution fails because of a compilation failure and for the next execution the source file is fixed,
                        // so only the one changed source file needs to be compiled.
                        // If there is no previous state, then we do have output changes
                        boolean shouldStore = result.getExecution().isSuccessful() || context.getPreviousExecutionState()
                            .map(previewExecutionState -> didOutputsChange(
                                previewExecutionState.getOutputFilesProducedByWork(),
                                afterExecutionState.getOutputFilesProducedByWork()))
                            .orElse(true);

                        if (shouldStore) {
                            history.store(
                                context.getIdentity().getUniqueId(),
                                result.getExecution().isSuccessful(),
                                afterExecutionState
                            );
                        }
                    }
                )
            );
        return result;
    }

    private static boolean didOutputsChange(ImmutableSortedMap<String, FileSystemSnapshot> previous, ImmutableSortedMap<String, FileSystemSnapshot> current) {
        // If there are different output properties compared to the previous execution, then we do have output changes
        if (!previous.keySet().equals(current.keySet())) {
            return true;
        }

        // Otherwise, do deep compare of outputs
        ChangeDetectorVisitor visitor = new ChangeDetectorVisitor();
        OutputFileChanges changes = new OutputFileChanges(previous, current);
        changes.accept(visitor);
        return visitor.hasAnyChanges();
    }
}
