// Copyright 2016 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.skyframe;

import static com.google.common.base.MoreObjects.firstNonNull;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.collect.ImmutableList.toImmutableList;

import com.google.common.base.MoreObjects;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;
import com.google.common.flogger.GoogleLogger;
import com.google.devtools.build.lib.bugreport.BugReport;
import com.google.devtools.build.lib.collect.nestedset.NestedSet;
import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
import com.google.devtools.build.lib.collect.nestedset.Order;
import com.google.devtools.build.lib.concurrent.QuiescingExecutor;
import com.google.devtools.build.lib.events.Event;
import com.google.devtools.build.lib.events.EventKind;
import com.google.devtools.build.lib.events.ExtendedEventHandler;
import com.google.devtools.build.lib.events.Reportable;
import com.google.devtools.build.skyframe.EvaluationProgressReceiver.EvaluationState;
import com.google.devtools.build.skyframe.NodeEntry.DependencyState;
import com.google.devtools.build.skyframe.QueryableGraph.LookupHint;
import com.google.devtools.build.skyframe.QueryableGraph.Reason;
import com.google.devtools.build.skyframe.proto.GraphInconsistency.Inconsistency;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.ForOverride;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.function.Supplier;
import javax.annotation.Nullable;

/**
 * A {@link SkyFunction.Environment} implementation for {@link ParallelEvaluator}.
 *
 * <p>The base {@link SkyFunctionEnvironment} class batch prefetches previously requested deps
 * during environment creation.
 *
 * <p>The {@link SkipsBatchPrefetch} subclass skips batch prefetching, so that it is more efficient
 * to create the environment when the number of previously requested deps is extremely large.
 */
// TODO: b/324948927 - Instead of having individual `SkyKey`s overriding the `skipsBatchPrefetch`
// method, some method similar to QueryableGraph#getLookupHint() when creating the environment to
// know whether batch prefetch should happen.
public class SkyFunctionEnvironment extends AbstractSkyFunctionEnvironment
    implements SkyframeLookupResult, ExtendedEventHandler {

  private static final GoogleLogger logger = GoogleLogger.forEnclosingClass();

  private static final SkyValue NULL_MARKER = new SkyValue() {};
  private static final SkyValue PENDING_MARKER = new SkyValue() {};
  private static final SkyValue MANUALLY_REGISTERED_MARKER = new SkyValue() {};

  private boolean building = true;
  private SkyKey depErrorKey = null;
  private final SkyKey skyKey;
  private final GroupedDeps previouslyRequestedDeps;

  /**
   * The deps requested during the previous build of this node. Used for two reasons: (1) They are
   * fetched eagerly before the node is built, to potentially prime the graph and speed up requests
   * for them during evaluation. (2) When the node finishes building, any deps from the previous
   * build that are not deps from this build must have this node removed from them as a reverse dep.
   * Thus, it is important that all nodes in this set have the property that they have this node as
   * a reverse dep from the last build, but that this node has not added them as a reverse dep on
   * this build. That set is normally {@link NodeEntry#getAllRemainingDirtyDirectDeps()}, but in
   * certain corner cases, like cycles, further filtering may be needed.
   */
  private final Set<SkyKey> oldDeps;

  private SkyValue value = null;
  private ErrorInfo errorInfo = null;

  @Nullable private Version maxTransitiveSourceVersion;

  /**
   * This is not {@code null} only during cycle detection and error bubbling. The nullness of this
   * field is used to detect whether evaluation is in one of those special states.
   *
   * <p>When this is not {@code null}, values in this map should be used (while getting
   * dependencies' values, events, or posts) over values from the graph for keys present in this
   * map.
   */
  @Nullable private final Map<SkyKey, ValueWithMetadata> bubbleErrorInfo;

  private boolean encounteredErrorDuringBubbling = false;

  /**
   * The values previously declared as dependencies during an earlier {@link SkyFunction#compute}
   * call for {@link #skyKey}.
   *
   * <p>Values in this map were generally retrieved via {@link NodeEntry#getValueMaybeWithMetadata}
   * from done nodes. In some cases, values may be {@link #NULL_MARKER} (see {@link #batchPrefetch}
   * for more details).
   *
   * <p>In {@link SkipsBatchPrefetch}, this map is not exhaustive. It populates as the {@link
   * SkyFunction} re-requests dep values, and will contain {@link #PENDING_MARKER}s when a key is
   * about to be requested from the graph.
   */
  private final Map<SkyKey, SkyValue> previouslyRequestedDepsValues;

  /**
   * The values newly requested from the graph during the {@link SkyFunction#compute} call for this
   * environment.
   *
   * <p>Values in this map were either retrieved via {@link NodeEntry#getValueMaybeWithMetadata} or
   * are one of the following special marker values:
   *
   * <ol>
   *   <li>{@link #NULL_MARKER}: The key was already requested from the graph but was either not
   *       present or not done.
   *   <li>{@link #PENDING_MARKER}: The key is about to be requested from the graph. This is a
   *       placeholder to detect duplicate keys in the same batch. It will be overwritten with
   *       either {@link #NULL_MARKER} or a value once it is requested.
   *   <li>{@link #MANUALLY_REGISTERED_MARKER}: The key was manually registered via {@link
   *       #registerDependencies} and has not been otherwise requested. Such keys are assumed to be
   *       done.
   * </ol>
   *
   * <p>This map is ordered to preserve dep groups. The sizes of each group are stored in {@link
   * #newlyRequestedDepGroupSizes}. On a subsequent build, if the value is dirty, all deps in the
   * same group can be checked in parallel for changes. In other words, if dep1 and dep2 are in the
   * same group, then dep1 will be checked in parallel with dep2. See {@link
   * SkyFunction.Environment#getValuesAndExceptions} for more.
   *
   * <p>Keys in this map are disjoint with {@link #previouslyRequestedDepsValues}. This map may
   * contain entries from {@link #bubbleErrorInfo} if they were requested.
   */
  private final Map<SkyKey, SkyValue> newlyRequestedDepsValues = new LinkedHashMap<>();

  /** Size delimiters for dep groups in {@link #newlyRequestedDepsValues}. */
  private final List<Integer> newlyRequestedDepGroupSizes = new ArrayList<>();

  /** The set of errors encountered while fetching children. */
  private final Set<ErrorInfo> childErrorInfos = new LinkedHashSet<>();

  private final ParallelEvaluatorContext evaluatorContext;

  private final List<Reportable> eventsToReport = new ArrayList<>();

  static SkyFunctionEnvironment create(
      SkyKey skyKey,
      GroupedDeps previouslyRequestedDeps,
      Set<SkyKey> oldDeps,
      @Nullable Version maxTransitiveSourceVersionSoFar,
      ParallelEvaluatorContext evaluatorContext)
      throws InterruptedException, UndonePreviouslyRequestedDeps {
    Version maxTransitiveSourceVersion =
        skyKey.functionName().getHermeticity() != FunctionHermeticity.NONHERMETIC
            ? firstNonNull(maxTransitiveSourceVersionSoFar, evaluatorContext.getMinimalVersion())
            : null;
    return skyKey.skipsBatchPrefetch()
        ? new SkyFunctionEnvironment.SkipsBatchPrefetch(
            skyKey, previouslyRequestedDeps, oldDeps, evaluatorContext, maxTransitiveSourceVersion)
        : new SkyFunctionEnvironment(
            skyKey,
            previouslyRequestedDeps,
            /* bubbleErrorInfo= */ null,
            oldDeps,
            evaluatorContext,
            /* throwIfPreviouslyRequestedDepsUndone= */ true,
            maxTransitiveSourceVersion);
  }

  static SkyFunctionEnvironment createForError(
      SkyKey skyKey,
      GroupedDeps previouslyRequestedDeps,
      Map<SkyKey, ValueWithMetadata> bubbleErrorInfo,
      Set<SkyKey> oldDeps,
      ParallelEvaluatorContext evaluatorContext)
      throws InterruptedException {
    try {
      return new SkyFunctionEnvironment(
          skyKey,
          previouslyRequestedDeps,
          checkNotNull(bubbleErrorInfo),
          oldDeps,
          evaluatorContext,
          /* throwIfPreviouslyRequestedDepsUndone= */ false,
          // Cycles can lead to a state where the versions of done children don't accurately reflect
          // the state that led to this node's value. Be conservative then.
          /* maxTransitiveSourceVersion= */ null);
    } catch (UndonePreviouslyRequestedDeps undonePreviouslyRequestedDeps) {
      throw new IllegalStateException(undonePreviouslyRequestedDeps);
    }
  }

  private SkyFunctionEnvironment(
      SkyKey skyKey,
      GroupedDeps previouslyRequestedDeps,
      @Nullable Map<SkyKey, ValueWithMetadata> bubbleErrorInfo,
      Set<SkyKey> oldDeps,
      ParallelEvaluatorContext evaluatorContext,
      boolean throwIfPreviouslyRequestedDepsUndone,
      @Nullable Version maxTransitiveSourceVersion)
      throws UndonePreviouslyRequestedDeps, InterruptedException {
    this.skyKey = checkNotNull(skyKey);
    this.previouslyRequestedDeps = checkNotNull(previouslyRequestedDeps);
    this.bubbleErrorInfo = bubbleErrorInfo;
    this.oldDeps = checkNotNull(oldDeps);
    this.evaluatorContext = checkNotNull(evaluatorContext);
    this.maxTransitiveSourceVersion = maxTransitiveSourceVersion;
    this.previouslyRequestedDepsValues = batchPrefetch(throwIfPreviouslyRequestedDepsUndone);
  }

  @ForOverride
  Map<SkyKey, SkyValue> batchPrefetch(boolean throwIfPreviouslyRequestedDepsUndone)
      throws InterruptedException, UndonePreviouslyRequestedDeps {
    ImmutableSet<SkyKey> excludedKeys =
        evaluatorContext.getGraph().prefetchDeps(skyKey, oldDeps, previouslyRequestedDeps);
    Collection<SkyKey> keysToPrefetch =
        excludedKeys != null ? excludedKeys : previouslyRequestedDeps.getAllElementsAsIterable();
    NodeBatch batch = evaluatorContext.getGraph().getBatch(skyKey, Reason.PREFETCH, keysToPrefetch);
    ImmutableMap.Builder<SkyKey, SkyValue> depValuesBuilder =
        ImmutableMap.builderWithExpectedSize(keysToPrefetch.size());
    ImmutableList.Builder<SkyKey> missingRequestedDeps = null;
    for (SkyKey depKey : keysToPrefetch) {
      NodeEntry entry = batch.get(depKey);
      if (entry == null) {
        if (missingRequestedDeps == null) {
          missingRequestedDeps = ImmutableList.builder();
        }
        missingRequestedDeps.add(depKey);
        continue;
      }

      SkyValue valueMaybeWithMetadata = entry.getValueMaybeWithMetadata();
      boolean depDone = valueMaybeWithMetadata != null;
      if (throwIfPreviouslyRequestedDepsUndone && !depDone) {
        // A previously requested dep may have transitioned from done to dirty between when the node
        // was read during a previous attempt to build this node and now. Notify the graph
        // inconsistency receiver so that we can crash if that's unexpected.
        evaluatorContext
            .getGraphInconsistencyReceiver()
            .noteInconsistencyAndMaybeThrow(
                skyKey, ImmutableList.of(depKey), Inconsistency.BUILDING_PARENT_FOUND_UNDONE_CHILD);
        throw new UndonePreviouslyRequestedDeps(ImmutableList.of(depKey));
      }
      depValuesBuilder.put(depKey, !depDone ? NULL_MARKER : valueMaybeWithMetadata);
      if (depDone) {
        maybeUpdateMaxTransitiveSourceVersion(entry);
      }
    }

    if (missingRequestedDeps != null) {
      // Notify `GraphInconsistencyReceiver` when there are some dependencies missing from the graph
      // to check whether this is expected.
      ImmutableList<SkyKey> allMissingDeps = missingRequestedDeps.build();
      evaluatorContext
          .getGraphInconsistencyReceiver()
          .noteInconsistencyAndMaybeThrow(
              skyKey, allMissingDeps, Inconsistency.ALREADY_DECLARED_CHILD_MISSING);
      throw new UndonePreviouslyRequestedDeps(allMissingDeps);
    }

    ImmutableMap<SkyKey, SkyValue> prefetched = depValuesBuilder.buildOrThrow();
    checkState(
        !prefetched.containsKey(ErrorTransienceValue.KEY),
        "%s cannot have a dep on ErrorTransienceValue during building",
        skyKey);
    return prefetched;
  }

  private void checkActive() {
    checkState(building, skyKey);
  }

  /**
   * Reports events which were temporarily stored in this environment per the specification of
   * {@link SkyFunction.Environment#getListener}. Returns events that should be stored for potential
   * replay on a future evaluation.
   */
  NestedSet<Reportable> reportEventsAndGetEventsToStore(NodeEntry entry, boolean expectDoneDeps)
      throws InterruptedException {
    EventFilter eventFilter = evaluatorContext.getStoredEventFilter();
    if (!eventFilter.storeEvents()) {
      if (!eventsToReport.isEmpty()) {
        String tag = getTagFromKey();
        for (Reportable event : eventsToReport) {
          event.withTag(tag).reportTo(evaluatorContext.getReporter());
        }
      }
      return NestedSetBuilder.emptySet(Order.STABLE_ORDER);
    }

    GroupedDeps depKeys = entry.getTemporaryDirectDeps();
    if (eventsToReport.isEmpty() && depKeys.isEmpty()) {
      return NestedSetBuilder.emptySet(Order.STABLE_ORDER);
    }

    NestedSetBuilder<Reportable> eventBuilder = NestedSetBuilder.stableOrder();
    if (!eventsToReport.isEmpty()) {
      String tag = getTagFromKey();
      eventBuilder.addAll(Lists.transform(eventsToReport, event -> event.withTag(tag)));
    }

    addTransitiveEventsFromDepValuesForDoneNode(
        eventBuilder,
        Iterables.filter(
            depKeys.getAllElementsAsIterable(),
            depKey -> eventFilter.shouldPropagate(depKey, skyKey)),
        expectDoneDeps);

    NestedSet<Reportable> events = eventBuilder.buildInterruptibly();
    evaluatorContext.getReplayingNestedSetEventVisitor().visit(events);
    return events;
  }

  /**
   * Adds transitive events from done deps in {@code depKeys}, by looking in order at:
   *
   * <ol>
   *   <li>{@link #bubbleErrorInfo}
   *   <li>{@link #previouslyRequestedDepsValues}
   *   <li>{@link #newlyRequestedDepsValues}
   *   <li>{@link #evaluatorContext}'s graph accessing methods
   * </ol>
   *
   * <p>Any key whose {@link NodeEntry}--or absence thereof--had to be read from the graph will also
   * be entered into {@link #newlyRequestedDepsValues} with its value or a {@link #NULL_MARKER}.
   *
   * <p>This asserts that only keys manually registered via {@link #registerDependencies} require
   * reading from the graph, because this node is done, and so all other deps must have been
   * previously or newly requested.
   *
   * <p>If {@code assertDone}, this asserts that all deps in {@code depKeys} are done.
   */
  private void addTransitiveEventsFromDepValuesForDoneNode(
      NestedSetBuilder<Reportable> eventBuilder, Iterable<SkyKey> depKeys, boolean assertDone)
      throws InterruptedException {
    // depKeys may contain keys in newlyRegisteredDeps whose values have not yet been retrieved from
    // the graph during this environment's lifetime.
    List<SkyKey> missingKeys = null;

    for (SkyKey key : depKeys) {
      SkyValue value = maybeGetValueFromErrorOrDeps(key);
      if (value == null) {
        if (key == ErrorTransienceValue.KEY) {
          continue;
        }
        checkState(
            newlyRequestedDepsValues.get(key) == MANUALLY_REGISTERED_MARKER,
            "Missing already declared dep %s (parent=%s)",
            key,
            skyKey);
        if (missingKeys == null) {
          missingKeys = new ArrayList<>();
        }
        missingKeys.add(key);
      } else if (value == NULL_MARKER) {
        checkState(!assertDone, "%s had not done %s", skyKey, key);
      } else {
        eventBuilder.addTransitive(ValueWithMetadata.getEvents(value));
      }
    }
    if (missingKeys == null) {
      return;
    }
    NodeBatch missingEntries =
        evaluatorContext.getGraph().getBatch(skyKey, Reason.DEP_REQUESTED, missingKeys);
    for (SkyKey key : missingKeys) {
      NodeEntry depEntry = missingEntries.get(key);
      SkyValue valueOrNullMarker = getValueOrNullMarker(depEntry);
      newlyRequestedDepsValues.put(key, valueOrNullMarker);
      if (valueOrNullMarker == NULL_MARKER) {
        // TODO(mschaller): handle registered deps that transitioned from done to dirty during eval
        // But how? Resetting the current node may not help, because this dep was *registered*, not
        // requested. For now, no node that gets registered as a dep is eligible for
        // intra-evaluation dirtying, so let it crash.
        checkState(!assertDone, "%s had not done: %s", skyKey, key);
        continue;
      }
      maybeUpdateMaxTransitiveSourceVersion(depEntry);
      eventBuilder.addTransitive(ValueWithMetadata.getEvents(valueOrNullMarker));
    }
  }

  void setValue(SkyValue newValue) {
    checkState(
        errorInfo == null && bubbleErrorInfo == null,
        "%s %s %s %s",
        skyKey,
        newValue,
        errorInfo,
        bubbleErrorInfo);
    checkState(value == null, "%s %s %s", skyKey, value, newValue);
    value = newValue;
  }

  /**
   * Set this node to be in error. The node's value must not have already been set. However, all
   * dependencies of this node <i>must</i> already have been registered, since this method may
   * register a dependence on the error transience node, which should always be the last dep.
   */
  void setError(NodeEntry state, ErrorInfo errorInfo) throws InterruptedException {
    checkState(value == null, "%s %s %s", skyKey, value, errorInfo);
    checkState(this.errorInfo == null, "%s %s %s", skyKey, this.errorInfo, errorInfo);

    if (errorInfo.isDirectlyTransient()) {
      NodeEntry errorTransienceNode =
          checkNotNull(
              evaluatorContext
                  .getGraph()
                  .get(skyKey, Reason.RDEP_ADDITION, ErrorTransienceValue.KEY),
              "Null error value? %s",
              skyKey);
      DependencyState triState;
      if (oldDeps.contains(ErrorTransienceValue.KEY)) {
        triState = errorTransienceNode.checkIfDoneForDirtyReverseDep(skyKey);
      } else {
        triState = errorTransienceNode.addReverseDepAndCheckIfDone(skyKey);
      }
      checkState(triState == DependencyState.DONE, "%s %s %s", skyKey, triState, errorInfo);
      state.addSingletonTemporaryDirectDep(ErrorTransienceValue.KEY);
      state.signalDep(evaluatorContext.getGraphVersion(), ErrorTransienceValue.KEY);
      maxTransitiveSourceVersion = null;
    }

    this.errorInfo = checkNotNull(errorInfo, skyKey);
  }

  /**
   * Returns a value, {@code null}, or {@link #NULL_MARKER} for the given key by looking in order
   * at:
   *
   * <ol>
   *   <li>{@link #bubbleErrorInfo}
   *   <li>{@link #previouslyRequestedDepsValues}
   *   <li>{@link #newlyRequestedDepsValues}
   * </ol>
   *
   * <p>Returns {@code null} if no entries for {@code key} were found in any of those three maps, or
   * if the key was manually registered via {@link #registerDependencies} but never requested.
   */
  @Nullable
  SkyValue maybeGetValueFromErrorOrDeps(SkyKey key) {
    if (bubbleErrorInfo != null) {
      ValueWithMetadata bubbleErrorInfoValue = bubbleErrorInfo.get(key);
      if (bubbleErrorInfoValue != null) {
        return bubbleErrorInfoValue;
      }
    }
    SkyValue directDepsValue = getPreviouslyRequestedDepValue(key);
    if (directDepsValue != null) {
      return directDepsValue;
    }
    directDepsValue = newlyRequestedDepsValues.get(key);
    return directDepsValue == MANUALLY_REGISTERED_MARKER ? null : directDepsValue;
  }

  /**
   * Gets the value of previously requested dep from either the env-scoped map or the {@link
   * #evaluatorContext}'s graph.
   *
   * <p>In {@link SkipsBatchPrefetch}, since previously requested deps values are not available
   * after environment creation, so it needs to query the {@link #evaluatorContext}'s graph on
   * demand.
   */
  @Nullable
  @ForOverride
  SkyValue getPreviouslyRequestedDepValue(SkyKey key) {
    return previouslyRequestedDepsValues.get(key);
  }

  @ForOverride
  @Nullable
  SkyValue lookupRequestedDep(SkyKey depKey) {
    checkArgument(
        !depKey.equals(ErrorTransienceValue.KEY),
        "Error transience key cannot be in requested deps of %s",
        skyKey);
    if (bubbleErrorInfo != null) {
      ValueWithMetadata bubbleErrorInfoValue = bubbleErrorInfo.get(depKey);
      if (bubbleErrorInfoValue != null) {
        newlyRequestedDepsValues.put(depKey, bubbleErrorInfoValue);
        return bubbleErrorInfoValue;
      }
    }
    SkyValue directDepsValue = previouslyRequestedDepsValues.get(depKey);
    if (directDepsValue != null) {
      return directDepsValue;
    }
    directDepsValue = newlyRequestedDepsValues.putIfAbsent(depKey, PENDING_MARKER);
    return directDepsValue == MANUALLY_REGISTERED_MARKER ? null : directDepsValue;
  }

  private void endDepGroup(int sizeBeforeRequest) {
    int newDeps = newlyRequestedDepsValues.size() - sizeBeforeRequest;
    if (newDeps > 0) {
      newlyRequestedDepGroupSizes.add(newDeps);
    }
  }

  private static SkyValue getValueOrNullMarker(@Nullable NodeEntry nodeEntry)
      throws InterruptedException {
    if (nodeEntry == null) {
      return NULL_MARKER;
    }
    SkyValue valueMaybeWithMetadata = nodeEntry.getValueMaybeWithMetadata();
    if (valueMaybeWithMetadata == null) {
      return NULL_MARKER;
    }
    return valueMaybeWithMetadata;
  }

  @Nullable
  @Override
  <E1 extends Exception, E2 extends Exception, E3 extends Exception, E4 extends Exception>
      SkyValue getValueOrThrowInternal(
          SkyKey depKey,
          @Nullable Class<E1> exceptionClass1,
          @Nullable Class<E2> exceptionClass2,
          @Nullable Class<E3> exceptionClass3,
          @Nullable Class<E4> exceptionClass4)
          throws E1, E2, E3, E4, InterruptedException {
    checkActive();
    int sizeBeforeRequest = newlyRequestedDepsValues.size();
    SkyValue depValue = lookupRequestedDep(depKey);
    if (depValue != null) {
      processDepValue(depKey, depValue);
    } else {
      NodeEntry depEntry = evaluatorContext.getGraph().get(skyKey, Reason.DEP_REQUESTED, depKey);
      depValue = processDepEntry(depKey, depEntry);
    }
    endDepGroup(sizeBeforeRequest);

    return unwrapOrThrow(
        depKey, depValue, exceptionClass1, exceptionClass2, exceptionClass3, exceptionClass4);
  }

  @CanIgnoreReturnValue
  @Override
  public SkyframeLookupResult getValuesAndExceptions(Iterable<? extends SkyKey> depKeys)
      throws InterruptedException {
    checkActive();

    // Lazily initialized when we encounter a missing key and the graph's lookup hint indicates that
    // the key should be requested in a batch. If the graph supports efficient lookups of individual
    // keys, we avoid constructing a list.
    List<SkyKey> missingKeys = null;

    int sizeBeforeRequest = newlyRequestedDepsValues.size();
    for (SkyKey depKey : depKeys) {
      SkyValue value = lookupRequestedDep(depKey);
      if (value == PENDING_MARKER) {
        continue; // Duplicate key in this request.
      }
      if (value != null) {
        processDepValue(depKey, value);
      } else if (evaluatorContext.getGraph().getLookupHint(depKey) == LookupHint.BATCH) {
        if (missingKeys == null) {
          missingKeys = new ArrayList<>();
        }
        missingKeys.add(depKey);
      } else {
        NodeEntry depEntry = evaluatorContext.getGraph().get(skyKey, Reason.DEP_REQUESTED, depKey);
        processDepEntry(depKey, depEntry);
      }
    }
    endDepGroup(sizeBeforeRequest);

    if (missingKeys != null) {
      NodeBatch missingEntries =
          evaluatorContext.getGraph().getBatch(skyKey, Reason.DEP_REQUESTED, missingKeys);
      for (SkyKey key : missingKeys) {
        processDepEntry(key, missingEntries.get(key));
      }
    }

    return this;
  }

  @ForOverride
  @CanIgnoreReturnValue
  SkyValue processDepEntry(SkyKey depKey, @Nullable NodeEntry depEntry)
      throws InterruptedException {
    SkyValue valueOrNullMarker = getValueOrNullMarker(depEntry);
    processDepValue(depKey, valueOrNullMarker);
    newlyRequestedDepsValues.put(depKey, valueOrNullMarker);
    if (valueOrNullMarker != NULL_MARKER) {
      maybeUpdateMaxTransitiveSourceVersion(depEntry);
    }
    return valueOrNullMarker;
  }

  void processDepValue(SkyKey depKey, SkyValue depValue) {
    if (depValue == NULL_MARKER) {
      valuesMissing = true;
      return;
    }

    ErrorInfo errorInfo = ValueWithMetadata.getMaybeErrorInfo(depValue);
    if (errorInfo == null) {
      return;
    }
    childErrorInfos.add(errorInfo);
    if (bubbleErrorInfo != null) {
      encounteredErrorDuringBubbling = true;
      // Set interrupted status, to try to prevent the calling SkyFunction from doing anything fancy
      // after this. SkyFunctions executed during error bubbling are supposed to (quickly) rethrow
      // errors or return a value/null (but there's currently no way to enforce this).
      Thread.currentThread().interrupt();
    }

    // If we get here, then the dep node is present and also (i) depends on a cycle or (ii) errorful
    // or (iii) both. The remaining question is whether or not to convey to the SkyFunction that the
    // dep node is missing.
    //
    // If the dep node depends on a cycle, then we always want the SkyFunction to act as though the
    // dep is missing (cycles are not supposed to be observable by SkyFunctions), so we always set
    // valuesMissing.
    //
    // If the dep node is errorful and we're in nokeep_going mode and not in error bubbling, then
    // the SkyFunction is not supposed to be able to observe the error and is supposed to act like
    // the dep is missing, so we set valuesMissing. In contrast, if we are in error bubbling, then
    // the SkyFunction is supposed to be able to observe the error (so as to have the chance to
    // produce an enriched error).
    //
    // If the dep node is errorful and we're in keep_going mode, then SkyFunction is supposed to be
    // able to observe the error (say, with a followup SkyframeLookupResult#getOrThrow) so we don't
    // set valuesMissing.
    if (!errorInfo.getCycleInfo().isEmpty()
        || (errorInfo.getException() != null
            && !evaluatorContext.keepGoing()
            && bubbleErrorInfo == null)) {
      valuesMissing = true;
      // We arbitrarily record the first child error if we are about to abort.
      if (!evaluatorContext.keepGoing() && depErrorKey == null) {
        depErrorKey = depKey;
      }
    }
  }

  @Nullable
  @Override // SkyframeLookupResult implementation.
  public <E1 extends Exception, E2 extends Exception, E3 extends Exception> SkyValue getOrThrow(
      SkyKey depKey,
      @Nullable Class<E1> exceptionClass1,
      @Nullable Class<E2> exceptionClass2,
      @Nullable Class<E3> exceptionClass3)
      throws E1, E2, E3 {
    return unwrapOrThrow(
        depKey,
        maybeGetValueFromErrorOrDeps(depKey),
        exceptionClass1,
        exceptionClass2,
        exceptionClass3,
        null);
  }

  @Override // SkyframeLookupResult implementation.
  public boolean queryDep(SkyKey depKey, QueryDepCallback resultCallback) {
    SkyValue maybeWrappedValue = maybeGetValueFromErrorOrDeps(depKey);
    if (maybeWrappedValue == null) {
      BugReport.sendNonFatalBugReport(
          new IllegalStateException(
              String.format("Value for %s was missing, this should never happen", depKey)));
      return false;
    }
    if (maybeWrappedValue == NULL_MARKER) {
      valuesMissing = true;
      return false;
    }
    if (!(maybeWrappedValue instanceof ValueWithMetadata wrappedValue)) {
      resultCallback.acceptValue(depKey, maybeWrappedValue);
      return true;
    }
    if (!wrappedValue.hasError()) {
      resultCallback.acceptValue(depKey, wrappedValue.getValue());
      return true;
    }

    // Otherwise, there's an error.
    @Nullable Object result = handleError(depKey, wrappedValue);
    if (result instanceof SkyValue skyValue) {
      resultCallback.acceptValue(depKey, skyValue);
      return true;
    }
    if (result instanceof Exception exception
        && resultCallback.tryHandleException(depKey, exception)) {
      return true;
    }
    valuesMissing = true;
    return false;
  }

  @Nullable
  private <E1 extends Exception, E2 extends Exception, E3 extends Exception, E4 extends Exception>
      SkyValue unwrapOrThrow(
          SkyKey depKey,
          SkyValue maybeWrappedValue,
          @Nullable Class<E1> exceptionClass1,
          @Nullable Class<E2> exceptionClass2,
          @Nullable Class<E3> exceptionClass3,
          @Nullable Class<E4> exceptionClass4)
          throws E1, E2, E3, E4 {
    if (maybeWrappedValue == null) {
      BugReport.sendNonFatalBugReport(
          new IllegalStateException(
              String.format("Value for %s was missing, this should never happen", depKey)));
      return null;
    }
    if (maybeWrappedValue == NULL_MARKER) {
      valuesMissing = true;
      return null;
    }
    if (!(maybeWrappedValue instanceof ValueWithMetadata wrappedValue)) {
      return maybeWrappedValue;
    }
    if (!wrappedValue.hasError()) {
      return wrappedValue.getValue();
    }

    // Otherwise, there's an error.
    @Nullable Object result = handleError(depKey, wrappedValue);
    if (result instanceof SkyValue skyValue) {
      return skyValue;
    }
    if (result instanceof Exception) {
      SkyFunctionException.throwIfInstanceOf(
          (Exception) result, exceptionClass1, exceptionClass2, exceptionClass3, exceptionClass4);
    }
    valuesMissing = true;
    return null;
  }

  /**
   * Processes wrapped values containing errors.
   *
   * @param depKey the dependency key, used only for error messages.
   * @param wrappedError an instance of ValueWithMetadata containing an error.
   * @return A {@code SkyValue} when a value is available in keepGoing mode, an {@code Exception}
   *     when one should be propagated or null otherwise.
   */
  @Nullable
  private Object handleError(SkyKey depKey, ValueWithMetadata wrappedError) {
    if (evaluatorContext.keepGoing()) {
      // In keepGoing mode, returns any computed value to the caller.
      SkyValue justValue = wrappedError.getValue();
      if (justValue != null) {
        return justValue;
      }
    }

    ErrorInfo errorInfo = wrappedError.getErrorInfo();
    @Nullable Exception exception = errorInfo.getException();

    if (exception == null) {
      // If there's no exception, there must be a cycle.
      checkState(
          !errorInfo.getCycleInfo().isEmpty(),
          "%s %s %s %s",
          skyKey,
          depKey,
          errorInfo,
          wrappedError);
    } else if (evaluatorContext.keepGoing() || bubbleErrorInfo != null) {
      // The exception may only propagate in keepGoing mode or during error bubbling.
      return exception;
    }
    return null;
  }

  /**
   * If {@code !keepGoing} and there is at least one dep in error, returns a dep in error. Otherwise
   * returns {@code null}.
   */
  @Nullable
  SkyKey getDepErrorKey() {
    return depErrorKey;
  }

  @Override
  public ExtendedEventHandler getListener() {
    checkActive();
    return this;
  }

  @Override
  public GroupedDeps getTemporaryDirectDeps() {
    return previouslyRequestedDeps;
  }

  @Override
  public void handle(Event event) {
    if (event.getKind() == EventKind.WARNING) {
      event = event.withTag(getTagFromKey());
      if (!evaluatorContext.getEmittedEventState().addWarning(event)) {
        return; // Duplicate warning.
      }
    }
    reportEvent(event);
  }

  @Override
  public void post(Postable obj) {
    reportEvent(obj);
  }

  private void reportEvent(Reportable event) {
    checkActive();
    if (event.storeForReplay()) {
      eventsToReport.add(event);
    } else {
      event.reportTo(evaluatorContext.getReporter());
    }
  }

  void doneBuilding() {
    building = false;
  }

  Set<SkyKey> getNewlyRequestedDeps() {
    return newlyRequestedDepsValues.keySet();
  }

  /** Adds newly requested dep keys to the node's temporary direct deps. */
  void addTemporaryDirectDepsTo(NodeEntry entry) {
    entry.addTemporaryDirectDepsInGroups(
        newlyRequestedDepsValues.keySet(), newlyRequestedDepGroupSizes);
  }

  void removeUndoneNewlyRequestedDeps() {
    if (!valuesMissing) {
      return;
    }
    Iterator<SkyValue> it = newlyRequestedDepsValues.values().iterator();
    for (int i = 0; i < newlyRequestedDepGroupSizes.size(); i++) {
      int groupSize = newlyRequestedDepGroupSizes.get(i);
      int newGroupSize = groupSize;
      for (int j = 0; j < groupSize; j++) {
        if (it.next() == NULL_MARKER) {
          it.remove();
          newGroupSize--;
        }
      }
      newlyRequestedDepGroupSizes.set(i, newGroupSize);
    }
  }

  boolean isAnyDirectDepErrorTransitivelyTransient() {
    checkState(
        bubbleErrorInfo == null,
        "Checking dep error transitive transience during error bubbling for: %s",
        skyKey);
    for (SkyValue skyValue : previouslyRequestedDepsValues.values()) {
      ErrorInfo maybeErrorInfo = ValueWithMetadata.getMaybeErrorInfo(skyValue);
      if (maybeErrorInfo != null && maybeErrorInfo.isTransitivelyTransient()) {
        return true;
      }
    }
    return false;
  }

  boolean isAnyNewlyRequestedDepErrorTransitivelyTransient() {
    checkState(
        bubbleErrorInfo == null,
        "Checking dep error transitive transience during error bubbling for: %s",
        skyKey);
    for (SkyValue skyValue : newlyRequestedDepsValues.values()) {
      ErrorInfo maybeErrorInfo = ValueWithMetadata.getMaybeErrorInfo(skyValue);
      if (maybeErrorInfo != null && maybeErrorInfo.isTransitivelyTransient()) {
        return true;
      }
    }
    return false;
  }

  Set<ErrorInfo> getChildErrorInfos() {
    return childErrorInfos;
  }

  /**
   * Applies the change to the graph (mostly) atomically and returns parents to potentially signal
   * and enqueue.
   *
   * <p>Parents should be enqueued unless (1) this node is being built after the main evaluation has
   * aborted, or (2) this node is being built with {@code --nokeep_going}, and so we are about to
   * shut down the main evaluation anyway.
   */
  Set<SkyKey> commitAndGetParents(NodeEntry primaryEntry) throws InterruptedException {
    // Construct the definitive error info, if there is one.
    if (errorInfo == null) {
      errorInfo =
          evaluatorContext
              .getErrorInfoManager()
              .getErrorInfoToUse(skyKey, value != null, childErrorInfos);
      // TODO(b/166268889, b/172223413): remove when fixed.
      if (errorInfo != null && errorInfo.getException() instanceof IOException) {
        String skyFunctionName = skyKey.functionName().getName();
        if (!skyFunctionName.startsWith("FILE")
            && !skyFunctionName.startsWith("DIRECTORY_LISTING")) {
          logger.atInfo().withCause(errorInfo.getException()).log(
              "Synthetic errorInfo for %s", skyKey);
        }
      }
    }

    // We have the following implications:
    // errorInfo == null => value != null => enqueueParents.
    // All these implications are strict:
    // (1) errorInfo != null && value != null happens for values with recoverable errors.
    // (2) value == null && enqueueParents happens for values that are found to have errors
    // during a --keep_going build.

    NestedSet<Reportable> events =
        reportEventsAndGetEventsToStore(
            primaryEntry, /* expectDoneDeps= */ !skyKey.supportsPartialReevaluation());

    SkyValue valueWithMetadata;
    if (value == null) {
      checkNotNull(errorInfo, "%s %s", skyKey, primaryEntry);
      valueWithMetadata = ValueWithMetadata.error(errorInfo, events);
    } else {
      valueWithMetadata = ValueWithMetadata.normal(value, errorInfo, events);
    }
    GroupedDeps temporaryDirectDeps = primaryEntry.getTemporaryDirectDeps();
    ImmutableSet<SkyKey> resetDeps = primaryEntry.getResetDirectDeps();
    if (!oldDeps.isEmpty() || !resetDeps.isEmpty()) {
      // Remove the rdep on this entry for each of 1) its old deps from a prior evaluation that are
      // no longer direct deps and 2) reset deps that were not requested again post-restart.
      ImmutableList<SkyKey> depsToRemove =
          ImmutableList.copyOf(
              Sets.difference(Sets.union(oldDeps, resetDeps), temporaryDirectDeps.toSet()));
      NodeBatch oldDepEntries =
          evaluatorContext.getGraph().getBatch(skyKey, Reason.RDEP_REMOVAL, depsToRemove);
      for (SkyKey key : depsToRemove) {
        NodeEntry oldDepEntry = checkNotNull(oldDepEntries.get(key), key);
        oldDepEntry.removeReverseDep(skyKey);
      }
    }

    // If this entry is dirty, setValue may not actually change it, if it determines that the data
    // being written now is the same as the data already present in the entry. We detect this case
    // by comparing versions before and after setting the value.
    Version previousVersion = primaryEntry.getVersion();
    Set<SkyKey> reverseDeps =
        primaryEntry.setValue(
            valueWithMetadata, evaluatorContext.getGraphVersion(), maxTransitiveSourceVersion);
    Version currentVersion = primaryEntry.getVersion();
    boolean changed = !currentVersion.equals(previousVersion);

    // Tell the receiver that this value was built. If currentVersion.equals(evaluationVersion), it
    // was evaluated this run, and so was changed. Otherwise, it is less than evaluationVersion, by
    // the Preconditions check above, and was not actually changed this run -- when it was written
    // above, its version stayed below this update's version, so its value remains the same.
    evaluatorContext
        .getProgressReceiver()
        .evaluated(
            skyKey,
            EvaluationState.get(value, changed),
            /* newValue= */ changed ? value : null,
            /* newError= */ changed ? errorInfo : null,
            temporaryDirectDeps);

    return reverseDeps;
  }

  @Nullable
  private String getTagFromKey() {
    return evaluatorContext.getSkyFunctions().get(skyKey.functionName()).extractTag(skyKey);
  }

  /**
   * Gets the latch that is counted down when an exception is thrown in {@code
   * AbstractQueueVisitor}. For use in tests to check if an exception actually was thrown. Calling
   * {@code AbstractQueueVisitor#awaitExceptionForTestingOnly} can throw a spurious {@link
   * InterruptedException} because {@link CountDownLatch#await} checks the interrupted bit before
   * returning, even if the latch is already at 0. See bug "testTwoErrors is flaky".
   */
  CountDownLatch getExceptionLatchForTesting() {
    return evaluatorContext.getVisitor().getExceptionLatchForTestingOnly();
  }

  @Override
  public boolean inErrorBubblingForSkyFunctionsThatCanFullyRecoverFromErrors() {
    return bubbleErrorInfo != null;
  }

  @Override
  public void registerDependencies(Iterable<SkyKey> keys) {
    checkState(
        maxTransitiveSourceVersion == null,
        "Dependency registration not supported when tracking max transitive source versions");
    int sizeBeforeRequest = newlyRequestedDepsValues.size();
    for (SkyKey key : keys) {
      if (!previouslyRequestedDepsValues.containsKey(key)) {
        newlyRequestedDepsValues.putIfAbsent(key, MANUALLY_REGISTERED_MARKER);
      }
    }
    endDepGroup(sizeBeforeRequest);
  }

  @Override
  public void injectVersionForNonHermeticFunction(Version version) {
    checkState(skyKey.functionName().getHermeticity() == FunctionHermeticity.NONHERMETIC, skyKey);
    checkState(
        maxTransitiveSourceVersion == null,
        "Multiple injected versions (%s, %s) for %s",
        maxTransitiveSourceVersion,
        version,
        skyKey);
    checkNotNull(version, skyKey);
    checkState(
        !evaluatorContext.getGraphVersion().lowerThan(version),
        "Invalid injected version (%s > %s) for %s",
        version,
        evaluatorContext.getGraphVersion(),
        skyKey);
    maxTransitiveSourceVersion = version;
  }

  void maybeUpdateMaxTransitiveSourceVersion(NodeEntry depEntry) {
    if (maxTransitiveSourceVersion == null
        || skyKey.functionName().getHermeticity() == FunctionHermeticity.NONHERMETIC) {
      return;
    }
    Version depMtsv = depEntry.getMaxTransitiveSourceVersion();
    if (depMtsv == null || maxTransitiveSourceVersion.atMost(depMtsv)) {
      maxTransitiveSourceVersion = depMtsv;
    }
  }

  @Override
  public String toString() {
    return MoreObjects.toStringHelper(this)
        .add("skyKey", skyKey)
        .add("oldDeps", oldDeps)
        .add("value", value)
        .add("errorInfo", errorInfo)
        .add("previouslyRequestedDepsValues", previouslyRequestedDepsValues)
        .add("newlyRequestedDepsValues", newlyRequestedDepsValues)
        .add("newlyRequestedDepGroupSizes", newlyRequestedDepGroupSizes)
        .add("childErrorInfos", childErrorInfos)
        .add("depErrorKey", depErrorKey)
        .add("maxTransitiveSourceVersion", maxTransitiveSourceVersion)
        .add("bubbleErrorInfo", bubbleErrorInfo)
        .add("evaluatorContext", evaluatorContext)
        .toString();
  }

  @Override
  public SkyframeLookupResult getLookupHandleForPreviouslyRequestedDeps() {
    checkActive();
    return this;
  }

  @SuppressWarnings("unchecked")
  @Override
  public <T extends SkyKeyComputeState> T getState(Supplier<T> stateSupplier) {
    return (T) evaluatorContext.stateCache().get(skyKey, k -> stateSupplier.get());
  }

  boolean encounteredErrorDuringBubbling() {
    return encounteredErrorDuringBubbling;
  }

  @Override
  @Nullable
  public Version getMaxTransitiveSourceVersionSoFar() {
    return maxTransitiveSourceVersion;
  }

  void ensurePreviouslyRequestedDepsFetched()
      throws UndonePreviouslyRequestedDeps, InterruptedException {
    // Do nothing; previously requested deps were already fetched and checked for done-ness in
    // batchPrefetch.
  }

  boolean wasNewlyRequestedDepNullForPartialReevaluation(SkyKey newlyRequestedDep) {
    return false;
  }

  /**
   * In the case when user intends to add a new parallelism, one approach is to aggregate the
   * existing skyframe-evaluator one and a new type of thread pool in a {@link
   * com.google.devtools.build.lib.concurrent.MultiThreadPoolsQuiescingExecutor} object, and inject
   * it into {@link ParallelEvaluatorContext}.
   */
  @Override
  public final QuiescingExecutor getParallelEvaluationExecutor() {
    return evaluatorContext.getExecutor();
  }

  /** Thrown during environment construction if a previously requested dep is no longer done. */
  static final class UndonePreviouslyRequestedDeps extends Exception {
    private final ImmutableList<SkyKey> depKeys;

    private UndonePreviouslyRequestedDeps(ImmutableList<SkyKey> depKeys) {
      this.depKeys = checkNotNull(depKeys);
    }

    ImmutableList<SkyKey> getDepKeys() {
      return depKeys;
    }
  }

  /**
   * The environment that skips eagerly batch prefetching previously requested deps during creation.
   * Instead, their values are read from the graph on demand, in the same way as newly requested
   * deps.
   *
   * <p>This subclass is created if the {@link SkyKey} supports partial reevaluation or opts to skip
   * batch prefetching previously requested deps values.
   *
   * <p>The {@link #ensurePreviouslyRequestedDepsFetched} method, which gets called prior to node
   * completion, isn't a no-op, because they weren't prefetched. They're needed for version, error,
   * and event data during node completion.
   *
   * <p>The {@link #wasNewlyRequestedDepNullForPartialReevaluation} method may return {@code true},
   * when the evaluator checks for a newly requested done dep to which the current node is being
   * added as an rdep, to ensure that dep's key gets delivered to this node's mailbox.
   */
  private static final class SkipsBatchPrefetch extends SkyFunctionEnvironment {

    private SkipsBatchPrefetch(
        SkyKey skyKey,
        GroupedDeps previouslyRequestedDeps,
        Set<SkyKey> oldDeps,
        ParallelEvaluatorContext evaluatorContext,
        @Nullable Version maxTransitiveSourceVersion)
        throws UndonePreviouslyRequestedDeps, InterruptedException {
      super(
          skyKey,
          previouslyRequestedDeps,
          /* bubbleErrorInfo= */ null,
          oldDeps,
          evaluatorContext,
          false,
          maxTransitiveSourceVersion);
    }

    @Override
    Map<SkyKey, SkyValue> batchPrefetch(boolean throwIfPreviouslyRequestedDepsUndone) {
      // Partial reevaluations don't prefetch all previously requested deps, because doing so is too
      // expensive, with how many more times those nodes get reevaluated.
      return new HashMap<>();
    }

    @Nullable
    @Override
    SkyValue getPreviouslyRequestedDepValue(SkyKey key) {
      SkyFunctionEnvironment env = this;
      if (!env.previouslyRequestedDeps.contains(key)) {
        return null;
      }
      SkyValue possibleValueInMap = env.previouslyRequestedDepsValues.get(key);
      if (possibleValueInMap != null) {
        return possibleValueInMap;
      }
      try {
        // TODO: b/324948927#comment14 - Figure out the approach to properly handle possible missing
        // or undone deps before expanding the usage of `SkipsBatchPrefetch` or making
        // `SkipsBatchPrefetch` as the default environment to create.
        NodeEntry depEntry =
            env.evaluatorContext.getGraph().get(env.skyKey, Reason.DEP_REQUESTED, key);
        return processDepEntry(key, depEntry);
      } catch (InterruptedException e) {
        throw new IllegalStateException("No interruption when getting depEntry from depGraph", e);
      }
    }

    @Nullable
    @Override
    SkyValue lookupRequestedDep(SkyKey depKey) {
      SkyFunctionEnvironment env = this;
      checkArgument(
          !depKey.equals(ErrorTransienceValue.KEY),
          "Error transience key cannot be in requested deps of %s",
          env.skyKey);
      if (env.previouslyRequestedDeps.contains(depKey)) {
        return env.previouslyRequestedDepsValues.putIfAbsent(depKey, PENDING_MARKER);
      }
      SkyValue directDepsValue = env.newlyRequestedDepsValues.putIfAbsent(depKey, PENDING_MARKER);
      return directDepsValue == MANUALLY_REGISTERED_MARKER ? null : directDepsValue;
    }

    @CanIgnoreReturnValue
    @Override
    SkyValue processDepEntry(SkyKey depKey, @Nullable NodeEntry depEntry)
        throws InterruptedException {
      SkyFunctionEnvironment env = this;
      SkyValue valueOrNullMarker = getValueOrNullMarker(depEntry);
      processDepValue(depKey, valueOrNullMarker);
      if (env.previouslyRequestedDeps.contains(depKey)) {
        env.previouslyRequestedDepsValues.put(depKey, valueOrNullMarker);
      } else {
        env.newlyRequestedDepsValues.put(depKey, valueOrNullMarker);
      }
      if (valueOrNullMarker != NULL_MARKER) {
        maybeUpdateMaxTransitiveSourceVersion(depEntry);
      }
      return valueOrNullMarker;
    }

    @Override
    void ensurePreviouslyRequestedDepsFetched()
        throws UndonePreviouslyRequestedDeps, InterruptedException {
      SkyFunctionEnvironment env = this;
      ImmutableList<SkyKey> keysToFetch =
          env.previouslyRequestedDeps.toSet().stream()
              .filter(k -> !env.previouslyRequestedDepsValues.containsKey(k))
              .collect(toImmutableList());
      NodeBatch batch =
          env.evaluatorContext.getGraph().getBatch(env.skyKey, Reason.PREFETCH, keysToFetch);
      ImmutableList.Builder<SkyKey> missingRequestedDeps = null;
      for (SkyKey depKey : keysToFetch) {
        NodeEntry entry = batch.get(depKey);
        if (entry == null) {
          if (missingRequestedDeps == null) {
            missingRequestedDeps = ImmutableList.builder();
          }
          missingRequestedDeps.add(depKey);
          continue;
        }
        SkyValue valueMaybeWithMetadata = entry.getValueMaybeWithMetadata();
        boolean depDone = valueMaybeWithMetadata != null;
        if (!depDone) {
          // A previously requested dep may have transitioned from done to dirty between when the
          // node was read during a previous attempt to build this node and now. Notify the graph
          // inconsistency receiver so that we can crash if that's unexpected.
          env.evaluatorContext
              .getGraphInconsistencyReceiver()
              .noteInconsistencyAndMaybeThrow(
                  env.skyKey,
                  ImmutableList.of(depKey),
                  Inconsistency.BUILDING_PARENT_FOUND_UNDONE_CHILD);
          throw new UndonePreviouslyRequestedDeps(ImmutableList.of(depKey));
        }
        env.previouslyRequestedDepsValues.put(depKey, valueMaybeWithMetadata);
        maybeUpdateMaxTransitiveSourceVersion(entry);
      }

      if (missingRequestedDeps != null) {
        // Notify `GraphInconsistencyReceiver` when there are some dependencies missing from the
        // graph to check whether this is expected.
        ImmutableList<SkyKey> allMissingDeps = missingRequestedDeps.build();
        env.evaluatorContext
            .getGraphInconsistencyReceiver()
            .noteInconsistencyAndMaybeThrow(
                env.skyKey, allMissingDeps, Inconsistency.ALREADY_DECLARED_CHILD_MISSING);
        throw new UndonePreviouslyRequestedDeps(allMissingDeps);
      }
    }

    @Override
    boolean wasNewlyRequestedDepNullForPartialReevaluation(SkyKey newlyRequestedDep) {
      SkyFunctionEnvironment env = this;
      return env.newlyRequestedDepsValues.get(newlyRequestedDep) == NULL_MARKER;
    }
  }
}