// Copyright 2014 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;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import com.google.common.base.Verify;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.ImmutableSortedSet;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.Artifact.SourceArtifact;
import com.google.devtools.build.lib.actions.ArtifactFactory;
import com.google.devtools.build.lib.actions.FailAction;
import com.google.devtools.build.lib.actions.MutableActionGraph.ActionConflictException;
import com.google.devtools.build.lib.analysis.RuleContext.InvalidExecGroupException;
import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
import com.google.devtools.build.lib.analysis.config.ConfigMatchingProvider;
import com.google.devtools.build.lib.analysis.config.CoreOptions;
import com.google.devtools.build.lib.analysis.config.Fragment;
import com.google.devtools.build.lib.analysis.configuredtargets.EnvironmentGroupConfiguredTarget;
import com.google.devtools.build.lib.analysis.configuredtargets.InputFileConfiguredTarget;
import com.google.devtools.build.lib.analysis.configuredtargets.OutputFileConfiguredTarget;
import com.google.devtools.build.lib.analysis.configuredtargets.PackageGroupConfiguredTarget;
import com.google.devtools.build.lib.analysis.configuredtargets.RuleConfiguredTarget;
import com.google.devtools.build.lib.analysis.starlark.StarlarkRuleConfiguredTargetUtil;
import com.google.devtools.build.lib.analysis.test.AnalysisFailure;
import com.google.devtools.build.lib.analysis.test.AnalysisFailureInfo;
import com.google.devtools.build.lib.cmdline.Label;
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.ThreadSafety.ThreadSafe;
import com.google.devtools.build.lib.events.Event;
import com.google.devtools.build.lib.events.EventHandler;
import com.google.devtools.build.lib.packages.AdvertisedProviderSet;
import com.google.devtools.build.lib.packages.Aspect;
import com.google.devtools.build.lib.packages.Attribute;
import com.google.devtools.build.lib.packages.ConfigurationFragmentPolicy;
import com.google.devtools.build.lib.packages.ConfigurationFragmentPolicy.MissingFragmentPolicy;
import com.google.devtools.build.lib.packages.ConstantRuleVisibility;
import com.google.devtools.build.lib.packages.EnvironmentGroup;
import com.google.devtools.build.lib.packages.InputFile;
import com.google.devtools.build.lib.packages.OutputFile;
import com.google.devtools.build.lib.packages.PackageGroup;
import com.google.devtools.build.lib.packages.PackageGroupsRuleVisibility;
import com.google.devtools.build.lib.packages.PackageSpecification;
import com.google.devtools.build.lib.packages.PackageSpecification.PackageGroupContents;
import com.google.devtools.build.lib.packages.Rule;
import com.google.devtools.build.lib.packages.RuleClass;
import com.google.devtools.build.lib.packages.RuleClass.ConfiguredTargetFactory.RuleErrorException;
import com.google.devtools.build.lib.packages.RuleVisibility;
import com.google.devtools.build.lib.packages.StarlarkProviderIdentifier;
import com.google.devtools.build.lib.packages.Target;
import com.google.devtools.build.lib.profiler.memory.CurrentRuleTracker;
import com.google.devtools.build.lib.skyframe.AspectValueKey;
import com.google.devtools.build.lib.skyframe.ConfiguredTargetAndData;
import com.google.devtools.build.lib.skyframe.ConfiguredTargetKey;
import com.google.devtools.build.lib.util.ClassName;
import com.google.devtools.build.lib.util.OrderedSetMultimap;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.TreeSet;
import java.util.stream.Collectors;
import javax.annotation.Nullable;

/**
 * This class creates {@link ConfiguredTarget} instances using a given {@link
 * ConfiguredRuleClassProvider}.
 */
@ThreadSafe
public final class ConfiguredTargetFactory {
  // This class is not meant to be outside of the analysis phase machinery and is only public
  // in order to be accessible from the .view.skyframe package.

  private final ConfiguredRuleClassProvider ruleClassProvider;

  public ConfiguredTargetFactory(ConfiguredRuleClassProvider ruleClassProvider) {
    this.ruleClassProvider = ruleClassProvider;
  }

  /**
   * Returns the visibility of the given target. Errors during package group resolution are reported
   * to the {@code AnalysisEnvironment}.
   */
  private NestedSet<PackageGroupContents> convertVisibility(
      OrderedSetMultimap<DependencyKind, ConfiguredTargetAndData> prerequisiteMap,
      EventHandler reporter,
      Target target,
      BuildConfiguration packageGroupConfiguration) {
    RuleVisibility ruleVisibility = target.getVisibility();
    if (ruleVisibility instanceof ConstantRuleVisibility) {
      return ((ConstantRuleVisibility) ruleVisibility).isPubliclyVisible()
          ? NestedSetBuilder.create(
              Order.STABLE_ORDER,
              PackageGroupContents.create(ImmutableList.of(PackageSpecification.everything())))
          : NestedSetBuilder.emptySet(Order.STABLE_ORDER);
    } else if (ruleVisibility instanceof PackageGroupsRuleVisibility) {
      PackageGroupsRuleVisibility packageGroupsVisibility =
          (PackageGroupsRuleVisibility) ruleVisibility;

      NestedSetBuilder<PackageGroupContents> result = NestedSetBuilder.stableOrder();
      for (Label groupLabel : packageGroupsVisibility.getPackageGroups()) {
        // PackageGroupsConfiguredTargets are always in the package-group configuration.
        TransitiveInfoCollection group =
            findPrerequisite(prerequisiteMap, groupLabel, packageGroupConfiguration);
        PackageSpecificationProvider provider = null;
        // group == null can only happen if the package group list comes
        // from a default_visibility attribute, because in every other case,
        // this missing link is caught during transitive closure visitation or
        // if the RuleConfiguredTargetGraph threw out a visibility edge
        // because if would have caused a cycle. The filtering should be done
        // in a single place, ConfiguredTargetGraph, but for now, this is the
        // minimally invasive way of providing a sane error message in case a
        // cycle is created by a visibility attribute.
        if (group != null) {
          provider = group.getProvider(PackageSpecificationProvider.class);
        }
        if (provider != null) {
          result.addTransitive(provider.getPackageSpecifications());
        } else {
          reporter.handle(Event.error(target.getLocation(),
              String.format("Label '%s' does not refer to a package group", groupLabel)));
        }
      }

      result.add(packageGroupsVisibility.getDirectPackages());
      return result.build();
    } else {
      throw new IllegalStateException("unknown visibility");
    }
  }

  private TransitiveInfoCollection findPrerequisite(
      OrderedSetMultimap<DependencyKind, ConfiguredTargetAndData> prerequisiteMap,
      Label label,
      BuildConfiguration config) {
    for (ConfiguredTargetAndData prerequisite :
        prerequisiteMap.get(DependencyKind.VISIBILITY_DEPENDENCY)) {
      if (prerequisite.getTarget().getLabel().equals(label)
          && Objects.equals(prerequisite.getConfiguration(), config)) {
        return prerequisite.getConfiguredTarget();
      }
    }
    return null;
  }

  /**
   * Invokes the appropriate constructor to create a {@link ConfiguredTarget} instance.
   *
   * <p>For use in {@code ConfiguredTargetFunction}.
   *
   * <p>Returns null if Skyframe deps are missing or upon certain errors.
   */
  @Nullable
  public final ConfiguredTarget createConfiguredTarget(
      AnalysisEnvironment analysisEnvironment,
      ArtifactFactory artifactFactory,
      Target target,
      BuildConfiguration config,
      BuildConfiguration hostConfig,
      ConfiguredTargetKey configuredTargetKey,
      OrderedSetMultimap<DependencyKind, ConfiguredTargetAndData> prerequisiteMap,
      ImmutableMap<Label, ConfigMatchingProvider> configConditions,
      @Nullable ToolchainCollection<ResolvedToolchainContext> toolchainContexts)
      throws InterruptedException, ActionConflictException, InvalidExecGroupException {
    if (target instanceof Rule) {
      try {
        CurrentRuleTracker.beginConfiguredTarget(((Rule) target).getRuleClassObject());
        return createRule(
            analysisEnvironment,
            (Rule) target,
            config,
            hostConfig,
            configuredTargetKey,
            prerequisiteMap,
            configConditions,
            toolchainContexts);
      } finally {
        CurrentRuleTracker.endConfiguredTarget();
      }
    }

    // Visibility, like all package groups, doesn't have a configuration
    NestedSet<PackageGroupContents> visibility =
        convertVisibility(prerequisiteMap, analysisEnvironment.getEventHandler(), target, null);
    if (target instanceof OutputFile) {
      OutputFile outputFile = (OutputFile) target;
      TargetContext targetContext =
          new TargetContext(
              analysisEnvironment,
              target,
              config,
              prerequisiteMap.get(DependencyKind.OUTPUT_FILE_RULE_DEPENDENCY),
              visibility);
      if (analysisEnvironment.getSkyframeEnv().valuesMissing()) {
        return null;
      }
      RuleConfiguredTarget rule =
          (RuleConfiguredTarget)
              targetContext.findDirectPrerequisite(
                  outputFile.getGeneratingRule().getLabel(),
                  // Don't pass a specific configuration, as we don't care what configuration the
                  // generating rule is in. There can only be one actual dependency here, which is
                  // the target that generated the output file.
                  Optional.empty());
      Verify.verifyNotNull(rule);
      Artifact artifact = rule.getArtifactByOutputLabel(outputFile.getLabel());
      return new OutputFileConfiguredTarget(targetContext, outputFile, rule, artifact);
    } else if (target instanceof InputFile) {
      InputFile inputFile = (InputFile) target;
      TargetContext targetContext =
          new TargetContext(
              analysisEnvironment,
              target,
              config,
              prerequisiteMap.get(DependencyKind.OUTPUT_FILE_RULE_DEPENDENCY),
              visibility);
      SourceArtifact artifact =
          artifactFactory.getSourceArtifact(
              inputFile.getExecPath(
                  analysisEnvironment.getStarlarkSemantics().experimentalSiblingRepositoryLayout()),
              inputFile.getPackage().getSourceRoot().get(),
              ConfiguredTargetKey.builder()
                  .setLabel(target.getLabel())
                  .setConfiguration(config)
                  .build());
      return new InputFileConfiguredTarget(targetContext, inputFile, artifact);
    } else if (target instanceof PackageGroup) {
      PackageGroup packageGroup = (PackageGroup) target;
      TargetContext targetContext =
          new TargetContext(
              analysisEnvironment,
              target,
              config,
              prerequisiteMap.get(DependencyKind.VISIBILITY_DEPENDENCY),
              visibility);
      return new PackageGroupConfiguredTarget(targetContext, packageGroup);
    } else if (target instanceof EnvironmentGroup) {
      TargetContext targetContext =
          new TargetContext(analysisEnvironment, target, config, ImmutableSet.of(), visibility);
      return new EnvironmentGroupConfiguredTarget(targetContext);
    } else {
      throw new AssertionError("Unexpected target class: " + target.getClass().getName());
    }
  }

  /**
   * Returns a set of user-friendly strings identifying <i>almost</i> all of the pieces of config
   * state required by a rule or aspect.
   *
   * <p>The returned config state includes things that are known to be required at the time when the
   * rule's/aspect's dependencies have already been analyzed but before it's been analyzed itself.
   * See {@link RuleConfiguredTargetBuilder#maybeAddRequiredConfigFragmentsProvider} for the
   * remaining pieces of config state.
   *
   * <p>The strings can be names of {@link Fragment}s, names of {@link
   * com.google.devtools.build.lib.analysis.config.FragmentOptions}, and labels of user-defined
   * options such as Starlark flags and Android feature flags.
   *
   * <p>If {@code configuration} is {@link CoreOptions.IncludeConfigFragmentsEnum#DIRECT}, the
   * result includes only the config state considered to be directly required by this rule/aspect.
   * If it's {@link CoreOptions.IncludeConfigFragmentsEnum#TRANSITIVE}, it also includes config
   * state needed by transitive dependencies. If it's {@link
   * CoreOptions.IncludeConfigFragmentEnum#OFF}, this method just returns an empty set.
   *
   * <p>{@code select()}s and toolchain dependencies are considered when looking at what config
   * state is required.
   *
   * <p>TODO: This doesn't yet support fragments required by either native or Starlark transitions.
   *
   * @param buildSettingLabel this rule's label if this is a rule that's a build setting, else empty
   * @param configuration the configuration for this rule/aspect
   * @param universallyRequiredFragments fragments that are always required even if not explicitly
   *     specified for this rule/aspect
   * @param configurationFragmentPolicy source of truth for the fragments required by this
   *     rule/aspect class definition
   * @param configConditions {@link com.google.devtools.build.lib.analysis.config.FragmentOptions}
   *     required by {@code select}s on this rule (empty if this is an aspect). This is a different
   *     type than the others: options and fragments are different concepts. There's some subtlety
   *     to their relationship (e.g. a {@link
   *     com.google.devtools.build.lib.analysis.config.FragmentOptions} can be associated with
   *     multiple {@link Fragment}s). Rather than trying to merge all results into a pure set of
   *     {@link Fragment}s we just allow the mix. In practice the conceptual dependencies remain
   *     clear enough without trying to resolve these subtleties.
   * @param prerequisites all prerequisites of this rule/aspect
   * @return An alphabetically ordered set of required fragments, options, and labels of
   *     user-defined options.
   */
  private static ImmutableSortedSet<String> getRequiredConfigFragments(
      Optional<Label> buildSettingLabel,
      BuildConfiguration configuration,
      Collection<Class<? extends Fragment>> universallyRequiredFragments,
      ConfigurationFragmentPolicy configurationFragmentPolicy,
      Collection<ConfigMatchingProvider> configConditions,
      Iterable<ConfiguredTargetAndData> prerequisites) {
    CoreOptions coreOptions = configuration.getOptions().get(CoreOptions.class);
    if (coreOptions.includeRequiredConfigFragmentsProvider
        == CoreOptions.IncludeConfigFragmentsEnum.OFF) {
      return ImmutableSortedSet.of();
    }

    ImmutableSortedSet.Builder<String> requiredFragments = ImmutableSortedSet.naturalOrder();

    // Add directly required fragments:

    // Fragments explicitly required by this rule via the native rule/aspect definition API:
    configurationFragmentPolicy
        .getRequiredConfigurationFragments()
        .forEach(fragment -> requiredFragments.add(ClassName.getSimpleNameWithOuter(fragment)));
    // Fragments explicitly required by this rule via the Starlark rule/aspect definition API:
    configurationFragmentPolicy
        .getRequiredStarlarkFragments()
        .forEach(
            starlarkName -> {
              requiredFragments.add(
                  ClassName.getSimpleNameWithOuter(
                      configuration.getStarlarkFragmentByName(starlarkName)));
            });
    // Fragments universally required by everything:
    universallyRequiredFragments.forEach(
        fragment -> requiredFragments.add(ClassName.getSimpleNameWithOuter(fragment)));
    // Fragments required by config_conditions this rule select()s on (for aspects should be empty):
    configConditions.forEach(
        configCondition -> requiredFragments.addAll(configCondition.getRequiredFragmentOptions()));
    // We consider build settings (which are both rules and configuration) to require themselves:
    if (buildSettingLabel.isPresent()) {
      requiredFragments.add(buildSettingLabel.get().toString());
    }

    // Optionally add transitively required fragments:
    requiredFragments.addAll(getRequiredConfigFragmentsFromDeps(configuration, prerequisites));
    return requiredFragments.build();
  }

  /**
   * Subset of {@link #getRequiredConfigFragments} that only returns fragments required by deps.
   * This includes:
   *
   * <ul>
   *   <li>Requirements transitively required by deps iff {@link
   *       CoreOptions#includeRequiredConfigFragmentsProvider} is {@link
   *       CoreOptions.IncludeConfigFragmentsEnum#TRANSITIVE},
   *   <li>Dependencies on Starlark build settings iff {@link
   *       CoreOptions#includeRequiredConfigFragmentsProvider} is not {@link
   *       CoreOptions.IncludeConfigFragmentsEnum#OFF}. These are considered direct requirements on
   *       the rule.
   * </ul>
   */
  private static ImmutableSet<String> getRequiredConfigFragmentsFromDeps(
      BuildConfiguration configuration, Iterable<ConfiguredTargetAndData> prerequisites) {

    TreeSet<String> requiredFragments = new TreeSet<>();
    CoreOptions coreOptions = configuration.getOptions().get(CoreOptions.class);
    if (coreOptions.includeRequiredConfigFragmentsProvider
        == CoreOptions.IncludeConfigFragmentsEnum.OFF) {
      return ImmutableSet.of();
    }

    for (ConfiguredTargetAndData prereq : prerequisites) {
      // If the rule depends on a Starlark build setting, conceptually that means the rule directly
      // requires that as an option (even though it's technically a dependency).
      BuildSettingProvider buildSettingProvider =
          prereq.getConfiguredTarget().getProvider(BuildSettingProvider.class);
      if (buildSettingProvider != null) {
        requiredFragments.add(buildSettingProvider.getLabel().toString());
      }
      if (coreOptions.includeRequiredConfigFragmentsProvider
          == CoreOptions.IncludeConfigFragmentsEnum.TRANSITIVE) {
        // Add fragments only required because the rule's transitive deps need them.
        RequiredConfigFragmentsProvider depProvider =
            prereq.getConfiguredTarget().getProvider(RequiredConfigFragmentsProvider.class);
        if (depProvider != null) {
          requiredFragments.addAll(depProvider.getRequiredConfigFragments());
        }
      }
    }

    return ImmutableSet.copyOf(requiredFragments);
  }

  /**
   * Factory method: constructs a RuleConfiguredTarget of the appropriate class, based on the rule
   * class. May return null if an error occurred.
   */
  @Nullable
  private ConfiguredTarget createRule(
      AnalysisEnvironment env,
      Rule rule,
      BuildConfiguration configuration,
      BuildConfiguration hostConfiguration,
      ConfiguredTargetKey configuredTargetKey,
      OrderedSetMultimap<DependencyKind, ConfiguredTargetAndData> prerequisiteMap,
      ImmutableMap<Label, ConfigMatchingProvider> configConditions,
      @Nullable ToolchainCollection<ResolvedToolchainContext> toolchainContexts)
      throws InterruptedException, ActionConflictException, InvalidExecGroupException {
    ConfigurationFragmentPolicy configurationFragmentPolicy =
        rule.getRuleClassObject().getConfigurationFragmentPolicy();
    // Visibility computation and checking is done for every rule.
    RuleContext ruleContext =
        new RuleContext.Builder(
                env,
                rule,
                ImmutableList.of(),
                configuration,
                hostConfiguration,
                ruleClassProvider.getPrerequisiteValidator(),
                configurationFragmentPolicy,
                configuredTargetKey)
            .setVisibility(convertVisibility(prerequisiteMap, env.getEventHandler(), rule, null))
            .setPrerequisites(transformPrerequisiteMap(prerequisiteMap, rule))
            .setConfigConditions(configConditions)
            .setUniversalFragments(ruleClassProvider.getUniversalFragments())
            .setToolchainContexts(toolchainContexts)
            .setConstraintSemantics(ruleClassProvider.getConstraintSemantics())
            .setRequiredConfigFragments(
                getRequiredConfigFragments(
                    rule.isBuildSetting() ? Optional.of(rule.getLabel()) : Optional.empty(),
                    configuration,
                    ruleClassProvider.getUniversalFragments(),
                    configurationFragmentPolicy,
                    configConditions.values(),
                    prerequisiteMap.values()))
            .build();

    List<NestedSet<AnalysisFailure>> analysisFailures = depAnalysisFailures(ruleContext);
    if (!analysisFailures.isEmpty()) {
      return erroredConfiguredTargetWithFailures(ruleContext, analysisFailures);
    }
    if (ruleContext.hasErrors()) {
      return erroredConfiguredTarget(ruleContext);
    }

    MissingFragmentPolicy missingFragmentPolicy =
        configurationFragmentPolicy.getMissingFragmentPolicy();

    try {
      if (missingFragmentPolicy != MissingFragmentPolicy.IGNORE
          && !configuration.hasAllFragments(
              configurationFragmentPolicy.getRequiredConfigurationFragments())) {
        if (missingFragmentPolicy == MissingFragmentPolicy.FAIL_ANALYSIS) {
          ruleContext.ruleError(
              missingFragmentError(
                  ruleContext, configurationFragmentPolicy, configuration.checksum()));
          return null;
        }
        // Otherwise missingFragmentPolicy == MissingFragmentPolicy.CREATE_FAIL_ACTIONS:
        return createFailConfiguredTarget(ruleContext);
      }
      if (rule.getRuleClassObject().isStarlark()) {
        // TODO(bazel-team): maybe merge with RuleConfiguredTargetBuilder?
        ConfiguredTarget target =
            StarlarkRuleConfiguredTargetUtil.buildRule(
                ruleContext,
                rule.getRuleClassObject().getAdvertisedProviders(),
                rule.getRuleClassObject().getConfiguredTargetFunction(),
                rule.getLocation(),
                env.getStarlarkSemantics(),
                ruleClassProvider.getToolsRepository());

        return target != null ? target : erroredConfiguredTarget(ruleContext);
      } else {
        RuleClass.ConfiguredTargetFactory<ConfiguredTarget, RuleContext, ActionConflictException>
            factory =
                rule.getRuleClassObject()
                    .<ConfiguredTarget, RuleContext, ActionConflictException>
                        getConfiguredTargetFactory();
        Preconditions.checkNotNull(factory, rule.getRuleClassObject());
        return factory.create(ruleContext);
      }
    } catch (RuleErrorException ruleErrorException) {
      // Returning null in this method is an indication a rule error occurred. Exceptions are not
      // propagated, as this would show a nasty stack trace to users, and only provide info
      // on one specific failure with poor messaging. By returning null, the caller can
      // inspect ruleContext for multiple errors and output thorough messaging on each.
      return erroredConfiguredTarget(ruleContext);
    }
  }

  private List<NestedSet<AnalysisFailure>> depAnalysisFailures(RuleContext ruleContext) {
    if (ruleContext.getConfiguration().allowAnalysisFailures()) {
      ImmutableList.Builder<NestedSet<AnalysisFailure>> analysisFailures = ImmutableList.builder();
      Iterable<? extends TransitiveInfoCollection> infoCollections =
          ruleContext.getConfiguredTargetMap().values();
      for (TransitiveInfoCollection infoCollection : infoCollections) {
        AnalysisFailureInfo failureInfo =
            infoCollection.get(AnalysisFailureInfo.STARLARK_CONSTRUCTOR);
        if (failureInfo != null) {
          analysisFailures.add(failureInfo.getCausesNestedSet());
        }
      }
      return analysisFailures.build();
    }
    // Analysis failures are only created and propagated if --allow_analysis_failures is
    // enabled, otherwise these result in actual rule errors which are not caught.
    return ImmutableList.of();
  }

  private ConfiguredTarget erroredConfiguredTargetWithFailures(
      RuleContext ruleContext, List<NestedSet<AnalysisFailure>> analysisFailures)
      throws ActionConflictException {
    RuleConfiguredTargetBuilder builder = new RuleConfiguredTargetBuilder(ruleContext);
    builder.addNativeDeclaredProvider(AnalysisFailureInfo.forAnalysisFailureSets(analysisFailures));
    builder.addProvider(RunfilesProvider.class, RunfilesProvider.simple(Runfiles.EMPTY));
    return builder.build();
  }

  /**
   * Returns a {@link ConfiguredTarget} which indicates that an analysis error occurred in
   * processing the target. In most cases, this returns null, which signals to callers that
   * the target failed to build and thus the build should fail. However, if analysis failures
   * are allowed in this build, this returns a stub {@link ConfiguredTarget} which contains
   * information about the failure.
   */
  @Nullable
  private ConfiguredTarget erroredConfiguredTarget(RuleContext ruleContext)
      throws ActionConflictException {
    if (ruleContext.getConfiguration().allowAnalysisFailures()) {
      ImmutableList.Builder<AnalysisFailure> analysisFailures = ImmutableList.builder();

      for (String errorMessage : ruleContext.getSuppressedErrorMessages()) {
        analysisFailures.add(new AnalysisFailure(ruleContext.getLabel(), errorMessage));
      }
      RuleConfiguredTargetBuilder builder = new RuleConfiguredTargetBuilder(ruleContext);
      builder.addNativeDeclaredProvider(
          AnalysisFailureInfo.forAnalysisFailures(analysisFailures.build()));
      builder.addProvider(RunfilesProvider.class, RunfilesProvider.simple(Runfiles.EMPTY));
      return builder.build();
    } else {
      // Returning a null ConfiguredTarget is an indication a rule error occurred. Exceptions are
      // not propagated, as this would show a nasty stack trace to users, and only provide info
      // on one specific failure with poor messaging. By returning null, the caller can
      // inspect ruleContext for multiple errors and output thorough messaging on each.
      return null;
    }
  }

  private String missingFragmentError(
      RuleContext ruleContext,
      ConfigurationFragmentPolicy configurationFragmentPolicy,
      String configurationId) {
    RuleClass ruleClass = ruleContext.getRule().getRuleClassObject();
    Set<Class<?>> missingFragments = new LinkedHashSet<>();
    for (Class<?> fragment : configurationFragmentPolicy.getRequiredConfigurationFragments()) {
      if (!ruleContext.getConfiguration().hasFragment(fragment.asSubclass(Fragment.class))) {
        missingFragments.add(fragment);
      }
    }
    Preconditions.checkState(!missingFragments.isEmpty());
    StringBuilder result = new StringBuilder();
    result.append("all rules of type " + ruleClass.getName() + " require the presence of ");
    result.append("all of [");
    result.append(
        missingFragments.stream().map(Class::getSimpleName).collect(Collectors.joining(",")));
    result.append("], but these were all disabled in configuration ").append(configurationId);
    return result.toString();
  }

  @VisibleForTesting
  public static OrderedSetMultimap<Attribute, ConfiguredTargetAndData> transformPrerequisiteMap(
      OrderedSetMultimap<DependencyKind, ConfiguredTargetAndData> map, Target target) {
    OrderedSetMultimap<Attribute, ConfiguredTargetAndData> result = OrderedSetMultimap.create();
    for (Map.Entry<DependencyKind, ConfiguredTargetAndData> entry : map.entries()) {
      if (entry.getKey() == DependencyKind.TOOLCHAIN_DEPENDENCY) {
        continue;
      }
      Attribute attribute = entry.getKey().getAttribute();
      result.put(attribute, entry.getValue());
    }

    return result;
  }

  /**
   * Constructs an {@link ConfiguredAspect}. Returns null if an error occurs; in that case, {@code
   * aspectFactory} should call one of the error reporting methods of {@link RuleContext}.
   */
  public ConfiguredAspect createAspect(
      AnalysisEnvironment env,
      ConfiguredTargetAndData associatedTarget,
      ImmutableList<Aspect> aspectPath,
      ConfiguredAspectFactory aspectFactory,
      Aspect aspect,
      OrderedSetMultimap<DependencyKind, ConfiguredTargetAndData> prerequisiteMap,
      ImmutableMap<Label, ConfigMatchingProvider> configConditions,
      @Nullable ResolvedToolchainContext toolchainContext,
      BuildConfiguration aspectConfiguration,
      BuildConfiguration hostConfiguration,
      AspectValueKey.AspectKey aspectKey)
      throws InterruptedException, ActionConflictException, InvalidExecGroupException {

    RuleContext.Builder builder =
        new RuleContext.Builder(
            env,
            associatedTarget.getTarget(),
            aspectPath,
            aspectConfiguration,
            hostConfiguration,
            ruleClassProvider.getPrerequisiteValidator(),
            aspect.getDefinition().getConfigurationFragmentPolicy(),
            aspectKey);

    Map<String, Attribute> aspectAttributes = mergeAspectAttributes(aspectPath);

    RuleContext ruleContext =
        builder
            .setVisibility(
                convertVisibility(
                    prerequisiteMap, env.getEventHandler(), associatedTarget.getTarget(), null))
            .setPrerequisites(
                transformPrerequisiteMap(prerequisiteMap, associatedTarget.getTarget()))
            .setAspectAttributes(aspectAttributes)
            .setConfigConditions(configConditions)
            .setUniversalFragments(ruleClassProvider.getUniversalFragments())
            .setToolchainContext(toolchainContext)
            .setConstraintSemantics(ruleClassProvider.getConstraintSemantics())
            .setRequiredConfigFragments(
                getRequiredConfigFragments(
                    /*buildSettingLabel=*/ Optional.empty(),
                    aspectConfiguration,
                    ruleClassProvider.getUniversalFragments(),
                    aspect.getDefinition().getConfigurationFragmentPolicy(),
                    /*configConditions=*/ ImmutableList.of(),
                    prerequisiteMap.values()))
            .build();

    // If allowing analysis failures, targets should be created as normal as possible, and errors
    // will be propagated via a hook elsewhere as AnalysisFailureInfo.
    boolean allowAnalysisFailures = ruleContext.getConfiguration().allowAnalysisFailures();

    if (ruleContext.hasErrors() && !allowAnalysisFailures) {
      return null;
    }

    ConfiguredAspect configuredAspect =
        aspectFactory.create(
            associatedTarget,
            ruleContext,
            aspect.getParameters(),
            ruleClassProvider.getToolsRepository());
    if (configuredAspect != null) {
      validateAdvertisedProviders(
          configuredAspect,
          aspectKey,
          aspect.getDefinition().getAdvertisedProviders(),
          associatedTarget.getTarget(),
          env.getEventHandler());
    }
    return configuredAspect;
  }

  private ImmutableMap<String, Attribute> mergeAspectAttributes(ImmutableList<Aspect> aspectPath) {
    if (aspectPath.isEmpty()) {
      return ImmutableMap.of();
    } else if (aspectPath.size() == 1) {
      return aspectPath.get(0).getDefinition().getAttributes();
    } else {

      LinkedHashMap<String, Attribute> aspectAttributes = new LinkedHashMap<>();
      for (Aspect underlyingAspect : aspectPath) {
        ImmutableMap<String, Attribute> currentAttributes = underlyingAspect.getDefinition()
            .getAttributes();
        for (Map.Entry<String, Attribute> kv : currentAttributes.entrySet()) {
          if (!aspectAttributes.containsKey(kv.getKey())) {
            aspectAttributes.put(kv.getKey(), kv.getValue());
          }
        }
      }
      return ImmutableMap.copyOf(aspectAttributes);
    }
  }

  private void validateAdvertisedProviders(
      ConfiguredAspect configuredAspect,
      AspectValueKey.AspectKey aspectKey,
      AdvertisedProviderSet advertisedProviders,
      Target target,
      EventHandler eventHandler) {
    if (advertisedProviders.canHaveAnyProvider()) {
      return;
    }
    for (Class<?> aClass : advertisedProviders.getNativeProviders()) {
      if (configuredAspect.getProvider(aClass.asSubclass(TransitiveInfoProvider.class)) == null) {
        eventHandler.handle(
            Event.error(
                target.getLocation(),
                String.format(
                    "Aspect '%s', applied to '%s', does not provide advertised provider '%s'",
                    aspectKey.getAspectClass().getName(),
                    target.getLabel(),
                    aClass.getSimpleName())));
      }
    }

    for (StarlarkProviderIdentifier providerId : advertisedProviders.getStarlarkProviders()) {
      if (configuredAspect.get(providerId) == null) {
        eventHandler.handle(
            Event.error(
                target.getLocation(),
                String.format(
                    "Aspect '%s', applied to '%s', does not provide advertised provider '%s'",
                    aspectKey.getAspectClass().getName(), target.getLabel(), providerId)));
      }
    }
  }

  /**
   * A pseudo-implementation for configured targets that creates fail actions for all declared
   * outputs, both implicit and explicit.
   */
  private static ConfiguredTarget createFailConfiguredTarget(RuleContext ruleContext)
      throws RuleErrorException, ActionConflictException {
    RuleConfiguredTargetBuilder builder = new RuleConfiguredTargetBuilder(ruleContext);
    if (!ruleContext.getOutputArtifacts().isEmpty()) {
      ruleContext.registerAction(new FailAction(ruleContext.getActionOwner(),
          ruleContext.getOutputArtifacts(), "Can't build this"));
    }
    builder.add(RunfilesProvider.class, RunfilesProvider.simple(Runfiles.EMPTY));
    return builder.build();
  }
}