// 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.packages;

import static com.google.common.base.MoreObjects.firstNonNull;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Joiner;
import com.google.common.base.Preconditions;
import com.google.common.collect.BiMap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.ImmutableSortedMap;
import com.google.common.collect.ImmutableSortedSet;
import com.google.common.collect.Interner;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.devtools.build.lib.bugreport.BugReport;
import com.google.devtools.build.lib.cmdline.Label;
import com.google.devtools.build.lib.cmdline.LabelConstants;
import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
import com.google.devtools.build.lib.cmdline.PackageIdentifier;
import com.google.devtools.build.lib.cmdline.RepositoryMapping;
import com.google.devtools.build.lib.cmdline.RepositoryName;
import com.google.devtools.build.lib.cmdline.TargetPattern;
import com.google.devtools.build.lib.collect.CollectionUtils;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadCompatible;
import com.google.devtools.build.lib.events.Event;
import com.google.devtools.build.lib.events.EventHandler;
import com.google.devtools.build.lib.events.EventKind;
import com.google.devtools.build.lib.events.ExtendedEventHandler.Postable;
import com.google.devtools.build.lib.packages.License.DistributionType;
import com.google.devtools.build.lib.packages.Package.Builder.DefaultPackageSettings;
import com.google.devtools.build.lib.packages.Package.Builder.PackageSettings;
import com.google.devtools.build.lib.packages.semantics.BuildLanguageOptions;
import com.google.devtools.build.lib.server.FailureDetails.FailureDetail;
import com.google.devtools.build.lib.server.FailureDetails.PackageLoading;
import com.google.devtools.build.lib.server.FailureDetails.PackageLoading.Code;
import com.google.devtools.build.lib.skyframe.serialization.DeserializationContext;
import com.google.devtools.build.lib.skyframe.serialization.ObjectCodec;
import com.google.devtools.build.lib.skyframe.serialization.SerializationContext;
import com.google.devtools.build.lib.skyframe.serialization.SerializationException;
import com.google.devtools.build.lib.util.DetailedExitCode;
import com.google.devtools.build.lib.vfs.Path;
import com.google.devtools.build.lib.vfs.PathFragment;
import com.google.devtools.build.lib.vfs.Root;
import com.google.devtools.build.lib.vfs.RootedPath;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.protobuf.CodedInputStream;
import com.google.protobuf.CodedOutputStream;
import java.io.IOException;
import java.io.PrintStream;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.TreeMap;
import javax.annotation.Nullable;
import net.starlark.java.eval.Module;
import net.starlark.java.eval.StarlarkSemantics;
import net.starlark.java.eval.StarlarkThread;
import net.starlark.java.spelling.SpellChecker;
import net.starlark.java.syntax.Location;

/**
 * A package, which is a container of {@link Rule}s, each of which contains a dictionary of named
 * attributes.
 *
 * <p>Package instances are intended to be immutable and for all practical purposes can be treated
 * as such. Note, however, that some member variables exposed via the public interface are not
 * strictly immutable, so until their types are guaranteed immutable we're not applying the
 * {@code @Immutable} annotation here.
 *
 * <p>This class should not be extended - it's only non-final for mocking!
 *
 * <p>When changing this class, make sure to make corresponding changes to serialization!
 */
@SuppressWarnings("JavaLangClash")
public class Package {
  /**
   * The "workspace name" of packages generated by Bzlmod to contain repo rules.
   *
   * <p>Normally, packages containing repo rules are differentiated from packages containing build
   * rules by the {@link PackageIdentifier}: The singular repo-rule-containing package is {@code
   * //external}. However, in Bzlmod, packages containing repo rules need to have meaningful {@link
   * PackageIdentifier}s, so there needs to be some other way to distinguish them from
   * build-rule-containing packages. We use the following magic string as the "workspace name" for
   * repo-rule-containing packages generated by Bzlmod.
   *
   * @see #isRepoRulePackage()
   */
  private static final String DUMMY_WORKSPACE_NAME_FOR_BZLMOD_PACKAGES = "__dummy_workspace_bzlmod";

  /** Common superclass for all name-conflict exceptions. */
  public static class NameConflictException extends Exception {
    private NameConflictException(String message) {
      super(message);
    }
  }

  /**
   * The repository identifier for this package.
   */
  private final PackageIdentifier packageIdentifier;

  private final boolean succinctTargetNotFoundErrors;

  /** The filename of this package's BUILD file. */
  private RootedPath filename;

  /**
   * The directory in which this package's BUILD file resides. All InputFile members of the packages
   * are located relative to this directory.
   */
  private Path packageDirectory;

  /**
   * The name of the workspace this package is in. Used as a prefix for the runfiles directory. This
   * can be set in the WORKSPACE file. This must be a valid target name.
   */
  private String workspaceName;

  /**
   * The name of the Bzlmod module associated with the repo this package is in. If this package is
   * not from a Bzlmod repo, this is empty. For repos generated by module extensions, this is the
   * name of the module hosting the extension.
   */
  private final Optional<String> associatedModuleName;

  /**
   * The version of the Bzlmod module associated with the repo this package is in. If this package
   * is not from a Bzlmod repo, this is empty. For repos generated by module extensions, this is the
   * version of the module hosting the extension.
   */
  private final Optional<String> associatedModuleVersion;

  /**
   * The root of the source tree in which this package was found. It is an invariant that {@code
   * sourceRoot.getRelative(packageId.getSourceRoot()).equals(packageDirectory)}. Returns {@link
   * Optional#empty} if this {@link Package} is derived from a WORKSPACE file.
   */
  private Optional<Root> sourceRoot;

  /**
   * The "Make" environment of this package, containing package-local definitions of "Make"
   * variables.
   */
  private ImmutableMap<String, String> makeEnv;

  /** The collection of all targets defined in this package, indexed by name. */
  private ImmutableSortedMap<String, Target> targets;

  /**
   * Default visibility for rules that do not specify it.
   */
  private RuleVisibility defaultVisibility;
  private boolean defaultVisibilitySet;

  /**
   * How to enforce config_setting visibility settings.
   *
   * <p>This is a temporary setting in service of https://github.com/bazelbuild/bazel/issues/12669.
   * After enough depot cleanup, config_setting will have the same visibility enforcement as all
   * other rules.
   */
  public enum ConfigSettingVisibilityPolicy {
    /** Don't enforce visibility for any config_setting. */
    LEGACY_OFF,
    /** Honor explicit visibility settings on config_setting, else  use //visibility:public. */
    DEFAULT_PUBLIC,
    /** Enforce config_setting visibility exactly the same as all other rules. */
    DEFAULT_STANDARD
  }

  private ConfigSettingVisibilityPolicy configSettingVisibilityPolicy;

  /**
   * Default package-level 'testonly' value for rules that do not specify it.
   */
  private boolean defaultTestOnly = false;

  /**
   * Default package-level 'deprecation' value for rules that do not specify it.
   */
  private String defaultDeprecation;

  /**
   * Default header strictness checking for rules that do not specify it.
   */
  private String defaultHdrsCheck;

  /**
   * The InputFile target corresponding to this package's BUILD file.
   */
  private InputFile buildFile;

  /**
   * True iff this package's BUILD files contained lexical or grammatical
   * errors, or experienced errors during evaluation, or semantic errors during
   * the construction of any rule.
   *
   * <p>Note: A package containing errors does not necessarily prevent a build;
   * if all the rules needed for a given build were constructed prior to the
   * first error, the build may proceed.
   */
  private boolean containsErrors;

  /**
   * The first detailed error encountered during this package's construction and evaluation, or
   * {@code null} if there were no such errors or all its errors lacked details.
   */
  @Nullable private FailureDetail failureDetail;

  /** The list of transitive closure of the Starlark file dependencies. */
  private ImmutableList<Label> starlarkFileDependencies;

  /** The package's default "package_metadata" attribute. */
  private ImmutableSet<Label> defaultPackageMetadata = ImmutableSet.of();

  /**
   * The package's default "licenses" and "distribs" attributes, as specified
   * in calls to licenses() and distribs() in the BUILD file.
   */
  // These sets contain the values specified by the most recent licenses() or
  // distribs() declarations encountered during package parsing:
  private License defaultLicense;
  private Set<License.DistributionType> defaultDistributionSet;

  /**
   * The map from each repository to that repository's remappings map. This is only used in the
   * //external package, it is an empty map for all other packages. For example, an entry of {"@foo"
   * : {"@x", "@y"}} indicates that, within repository foo, "@x" should be remapped to "@y".
   */
  private ImmutableMap<RepositoryName, ImmutableMap<String, RepositoryName>>
      externalPackageRepositoryMappings;

  /**
   * The map of repository reassignments for BUILD packages. This will be empty for packages within
   * the main workspace.
   */
  private RepositoryMapping repositoryMapping;

  /**
   * The repository mapping of the main repository. This is only used internally to obtain
   * user-friendly apparent names from canonical repository names in error message arising from this
   * package.
   */
  private RepositoryMapping mainRepositoryMapping;

  private Set<Label> defaultCompatibleWith = ImmutableSet.of();
  private Set<Label> defaultRestrictedTo = ImmutableSet.of();

  private ImmutableSet<String> features;

  private ImmutableList<TargetPattern> registeredExecutionPlatforms;
  private ImmutableList<TargetPattern> registeredToolchains;

  private long computationSteps;

  private ImmutableMap<String, Module> loads;

  /** Returns the number of Starlark computation steps executed by this BUILD file. */
  public long getComputationSteps() {
    return computationSteps;
  }

  /**
   * Returns the mapping, for each load statement in this BUILD file in source order, from the load
   * string to the module it loads. It thus indirectly records the package's complete load DAG. In
   * some configurations the information may be unavailable (null).
   */
  @Nullable
  public ImmutableMap<String, Module> getLoads() {
    return loads;
  }

  /**
   * Package initialization, part 1 of 3: instantiates a new package with the given name.
   *
   * <p>As part of initialization, {@link Builder} constructs {@link InputFile} and {@link
   * PackageGroup} instances that require a valid Package instance where {@link
   * Package#getNameFragment()} is accessible. That's why these settings are applied here at the
   * start.
   *
   * <p>{@code name} <b>MUST</b> be a suffix of {@code filename.getParentDirectory())}.
   */
  private Package(
      PackageIdentifier packageId,
      String workspaceName,
      Optional<String> associatedModuleName,
      Optional<String> associatedModuleVersion,
      boolean succinctTargetNotFoundErrors) {
    this.packageIdentifier = packageId;
    this.workspaceName = workspaceName;
    this.associatedModuleName = associatedModuleName;
    this.associatedModuleVersion = associatedModuleVersion;
    this.succinctTargetNotFoundErrors = succinctTargetNotFoundErrors;
  }

  /** Returns this packages' identifier. */
  public PackageIdentifier getPackageIdentifier() {
    return packageIdentifier;
  }

  /**
   * Whether this package should contain only repo rules (returns {@code true}) or only build rules
   * (returns {@code false}).
   */
  private boolean isRepoRulePackage() {
    return packageIdentifier.equals(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER)
        || workspaceName.equals(DUMMY_WORKSPACE_NAME_FOR_BZLMOD_PACKAGES);
  }

  /**
   * Returns the repository mapping for the requested external repository.
   *
   * @throws UnsupportedOperationException if called from a package other than the //external
   *     package
   */
  public ImmutableMap<String, RepositoryName> getRepositoryMapping(RepositoryName repository) {
    if (!isRepoRulePackage()) {
      throw new UnsupportedOperationException("Can only access the external package repository"
          + "mappings from the //external package");
    }
    return externalPackageRepositoryMappings.getOrDefault(repository, ImmutableMap.of());
  }

  /** Get the repository mapping for this package. */
  public RepositoryMapping getRepositoryMapping() {
    return repositoryMapping;
  }

  /**
   * Returns the full map of repository mappings collected so far.
   *
   * @throws UnsupportedOperationException if called from a package other than the //external
   *     package
   */
  ImmutableMap<RepositoryName, ImmutableMap<String, RepositoryName>>
      getExternalPackageRepositoryMappings() {
    if (!isRepoRulePackage()) {
      throw new UnsupportedOperationException(
          "Can only access the external package repository"
              + "mappings from the //external package");
    }
    return this.externalPackageRepositoryMappings;
  }

  /**
   * Package initialization: part 2 of 3: sets this package's default header
   * strictness checking.
   *
   * <p>This is needed to support C++-related rule classes
   * which accesses {@link #getDefaultHdrsCheck} from the still-under-construction
   * package.
   */
  private void setDefaultHdrsCheck(String defaultHdrsCheck) {
    this.defaultHdrsCheck = defaultHdrsCheck;
  }

  /**
   * Set the default 'testonly' value for this package.
   */
  private void setDefaultTestOnly(boolean testOnly) {
    defaultTestOnly = testOnly;
  }

  /**
   * Set the default 'deprecation' value for this package.
   */
  private void setDefaultDeprecation(String deprecation) {
    defaultDeprecation = deprecation;
  }

  /**
   * Sets the default value to use for a rule's {@link RuleClass#COMPATIBLE_ENVIRONMENT_ATTR}
   * attribute when not explicitly specified by the rule.
   */
  private void setDefaultCompatibleWith(Set<Label> environments) {
    defaultCompatibleWith = environments;
  }

  /**
   * Sets the default value to use for a rule's {@link RuleClass#RESTRICTED_ENVIRONMENT_ATTR}
   * attribute when not explicitly specified by the rule.
   */
  private void setDefaultRestrictedTo(Set<Label> environments) {
    defaultRestrictedTo = environments;
  }

  /**
   * Returns the source root (a directory) beneath which this package's BUILD file was found, or
   * {@link Optional#empty} if this package was derived from a workspace file.
   *
   * <p>Assumes invariant: If non-empty, {@code
   * getSourceRoot().get().getRelative(packageId.getSourceRoot()).equals(getPackageDirectory())}
   */
  public Optional<Root> getSourceRoot() {
    return sourceRoot;
  }

  private static Root getSourceRoot(RootedPath buildFileRootedPath, PathFragment packageFragment) {
    PathFragment packageDirectory = buildFileRootedPath.getRootRelativePath().getParentDirectory();
    if (packageFragment.equals(packageDirectory)) {
      // Fast path: BUILD file path and package name are the same, don't create an extra root.
      return buildFileRootedPath.getRoot();
    }
    PathFragment current = buildFileRootedPath.asPath().asFragment().getParentDirectory();
    for (int i = 0, len = packageFragment.segmentCount(); i < len && current != null; i++) {
      current = current.getParentDirectory();
    }
    if (current == null || current.isEmpty()) {
      // This is never really expected to work. The check below in #finishInit should fail.
      return buildFileRootedPath.getRoot();
    }
    // Note that current is an absolute path.
    return Root.fromPath(buildFileRootedPath.getRoot().getRelative(current));
  }

  /**
   * Package initialization: part 3 of 3: applies all other settings and completes
   * initialization of the package.
   *
   * <p>Only after this method is called can this package be considered "complete"
   * and be shared publicly.
   */
  private void finishInit(Builder builder) {
    this.filename = builder.getFilename();
    this.packageDirectory = filename.asPath().getParentDirectory();
    String baseName = filename.getRootRelativePath().getBaseName();

    if (isWorkspaceFile(baseName) || isModuleDotBazelFile(baseName)) {
      Preconditions.checkState(isRepoRulePackage());
      this.sourceRoot = Optional.empty();
    } else {
      Root sourceRoot = getSourceRoot(filename, packageIdentifier.getSourceRoot());
      if (sourceRoot.asPath() == null
          || !sourceRoot.getRelative(packageIdentifier.getSourceRoot()).equals(packageDirectory)) {
        throw new IllegalArgumentException(
            "Invalid BUILD file name for package '"
                + packageIdentifier
                + "': "
                + filename
                + " (in source "
                + sourceRoot
                + " with packageDirectory "
                + packageDirectory
                + " and package identifier source root "
                + packageIdentifier.getSourceRoot()
                + ")");
      }
      this.sourceRoot = Optional.of(sourceRoot);
    }

    this.makeEnv = ImmutableMap.copyOf(builder.makeEnv);
    this.targets = ImmutableSortedMap.copyOf(builder.targets);
    this.defaultVisibility = builder.defaultVisibility;
    this.defaultVisibilitySet = builder.defaultVisibilitySet;
    this.configSettingVisibilityPolicy = builder.configSettingVisibilityPolicy;
    this.buildFile = builder.buildFile;
    this.containsErrors |= builder.containsErrors;
    this.failureDetail = builder.getFailureDetail();
    this.starlarkFileDependencies = builder.starlarkFileDependencies;
    this.defaultLicense = builder.defaultLicense;
    this.defaultDistributionSet = builder.defaultDistributionSet;
    this.defaultPackageMetadata = ImmutableSortedSet.copyOf(builder.defaultPackageMetadata);
    this.features = ImmutableSortedSet.copyOf(builder.features);
    this.registeredExecutionPlatforms = ImmutableList.copyOf(builder.registeredExecutionPlatforms);
    this.registeredToolchains = ImmutableList.copyOf(builder.registeredToolchains);
    this.repositoryMapping = Preconditions.checkNotNull(builder.repositoryMapping);
    this.mainRepositoryMapping = Preconditions.checkNotNull(builder.mainRepositoryMapping);
    ImmutableMap.Builder<RepositoryName, ImmutableMap<String, RepositoryName>>
        repositoryMappingsBuilder = ImmutableMap.builder();
    if (!builder.externalPackageRepositoryMappings.isEmpty() && !builder.isRepoRulePackage()) {
      // 'repo_mapping' should only be used in the //external package, i.e. should only appear
      // in WORKSPACE files. Currently, if someone tries to use 'repo_mapping' in a BUILD rule, they
      // will get a "no such attribute" error. This check is to protect against a 'repo_mapping'
      // attribute being added to a rule in the future.
      throw new IllegalArgumentException(
          "'repo_mapping' may only be used in the //external package");
    }
    builder.externalPackageRepositoryMappings.forEach((k, v) ->
        repositoryMappingsBuilder.put(k, ImmutableMap.copyOf(v)));
    this.externalPackageRepositoryMappings = repositoryMappingsBuilder.buildOrThrow();
  }

  private static boolean isWorkspaceFile(String baseFileName) {
    return baseFileName.equals(LabelConstants.WORKSPACE_DOT_BAZEL_FILE_NAME.getPathString())
        || baseFileName.equals(LabelConstants.WORKSPACE_FILE_NAME.getPathString());
  }

  private static boolean isModuleDotBazelFile(String baseFileName) {
    return baseFileName.equals(LabelConstants.MODULE_DOT_BAZEL_FILE_NAME.getPathString());
  }

  /** Returns the list of transitive closure of the Starlark file dependencies of this package. */
  public ImmutableList<Label> getStarlarkFileDependencies() {
    return starlarkFileDependencies;
  }

  /**
   * Returns the filename of the BUILD file which defines this package. The parent directory of the
   * BUILD file is the package directory.
   */
  public RootedPath getFilename() {
    return filename;
  }

  /**
   * Returns the directory containing the package's BUILD file.
   */
  public Path getPackageDirectory() {
    return packageDirectory;
  }

  /**
   * Returns the name of this package. If this build is using external repositories then this name
   * may not be unique!
   */
  public String getName() {
    return packageIdentifier.getPackageFragment().getPathString();
  }

  /**
   * Like {@link #getName}, but has type {@code PathFragment}.
   */
  public PathFragment getNameFragment() {
    return packageIdentifier.getPackageFragment();
  }

  /**
   * Returns all make variables for a given platform.
   */
  public ImmutableMap<String, String> getMakeEnvironment() {
    return makeEnv;
  }

  /**
   * Returns the label of this package's BUILD file.
   *
   * <p> Typically <code>getBuildFileLabel().getName().equals("BUILD")</code> --
   * though not necessarily: data in a subdirectory of a test package may use a
   * different filename to avoid inadvertently creating a new package.
   */
  public Label getBuildFileLabel() {
    return buildFile.getLabel();
  }

  /**
   * Returns the InputFile target for this package's BUILD file.
   */
  public InputFile getBuildFile() {
    return buildFile;
  }

  /**
   * Returns true if errors were encountered during evaluation of this package.
   * (The package may be incomplete and its contents should not be relied upon
   * for critical operations. However, any Rules belonging to the package are
   * guaranteed to be intact, unless their <code>containsErrors()</code> flag
   * is set.)
   */
  public boolean containsErrors() {
    return containsErrors;
  }

  void setContainsErrors() {
    containsErrors = true;
  }

  /**
   * Returns the first {@link FailureDetail} describing one of the package's errors, or {@code null}
   * if it has no errors or all its errors lack details.
   */
  @Nullable
  public FailureDetail getFailureDetail() {
    return failureDetail;
  }

  /**
   * Returns a {@link FailureDetail} attributing a target error to the package's {@link
   * FailureDetail}, or a generic {@link Code#TARGET_MISSING} failure detail if the package has
   * none.
   *
   * <p>May only be called when {@link #containsErrors()} is true and with a target whose package is
   * this one.
   */
  public FailureDetail contextualizeFailureDetailForTarget(Target target) {
    Preconditions.checkState(
        target.getPackage().packageIdentifier.equals(packageIdentifier),
        "contextualizeFailureDetailForTarget called for target not in package. target=%s,"
            + " package=%s",
        target,
        this);
    Preconditions.checkState(
        containsErrors,
        "contextualizeFailureDetailForTarget called for package not in error. target=%s",
        target);
    String prefix =
        "Target '" + target.getLabel() + "' contains an error and its package is in error";
    if (failureDetail == null) {
      return FailureDetail.newBuilder()
          .setMessage(prefix)
          .setPackageLoading(PackageLoading.newBuilder().setCode(Code.TARGET_MISSING))
          .build();
    }
    return failureDetail.toBuilder().setMessage(prefix + ": " + failureDetail.getMessage()).build();
  }

  /** Returns an (immutable, ordered) view of all the targets belonging to this package. */
  public ImmutableSortedMap<String, Target> getTargets() {
    return targets;
  }

  /** Common getTargets implementation, accessible by {@link Package.Builder}. */
  private static Set<Target> getTargets(BiMap<String, Target> targetMap) {
    return targetMap.values();
  }

  /**
   * Returns a (read-only, ordered) iterable of all the targets belonging
   * to this package which are instances of the specified class.
   */
  public <T extends Target> Iterable<T> getTargets(Class<T> targetClass) {
    return getTargets(targets, targetClass);
  }

  /**
   * Common getTargets implementation, accessible by both {@link Package} and
   * {@link Package.Builder}.
   */
  private static <T extends Target> Iterable<T> getTargets(Map<String, Target> targetMap,
      Class<T> targetClass) {
    return Iterables.filter(targetMap.values(), targetClass);
  }

  /**
   * Returns the rule that corresponds to a particular BUILD target name. Useful
   * for walking through the dependency graph of a target.
   * Fails if the target is not a Rule.
   */
  public Rule getRule(String targetName) {
    return (Rule) targets.get(targetName);
  }

  /**
   * Returns this package's workspace name.
   */
  public String getWorkspaceName() {
    return workspaceName;
  }

  /**
   * Returns the features specified in the <code>package()</code> declaration.
   */
  public ImmutableSet<String> getFeatures() {
    return features;
  }

  /**
   * Returns the target (a member of this package) whose name is "targetName".
   * First rules are searched, then output files, then input files.  The target
   * name must be valid, as defined by {@code LabelValidator#validateTargetName}.
   *
   * @throws NoSuchTargetException if the specified target was not found.
   */
  public Target getTarget(String targetName) throws NoSuchTargetException {
    Target target = targets.get(targetName);
    if (target != null) {
      return target;
    }

    Label label;
    try {
      label = Label.create(packageIdentifier, targetName);
    } catch (LabelSyntaxException e) {
      throw new IllegalArgumentException(targetName, e);
    }

    if (succinctTargetNotFoundErrors) {
      throw new NoSuchTargetException(
          label, String.format("target '%s' not declared in package '%s'", targetName, getName()));
    } else {
      String alternateTargetSuggestion = getAlternateTargetSuggestion(targetName);
      throw new NoSuchTargetException(
          label,
          String.format(
              "target '%s' not declared in package '%s' defined by %s%s",
              targetName, getName(), filename.asPath().getPathString(), alternateTargetSuggestion));
    }
  }

  private String getAlternateTargetSuggestion(String targetName) {
    // If there's a file on the disk that's not mentioned in the BUILD file,
    // produce a more informative error.  NOTE! this code path is only executed
    // on failure, which is (relatively) very rare.  In the common case no
    // stat(2) is executed.
    Path filename = packageDirectory.getRelative(targetName);
    if (!PathFragment.isNormalized(targetName) || "*".equals(targetName)) {
      // Don't check for file existence if the target name is not normalized
      // because the error message would be confusing and wrong. If the
      // targetName is "foo/bar/.", and there is a directory "foo/bar", it
      // doesn't mean that "//pkg:foo/bar/." is a valid label.
      // Also don't check if the target name is a single * character since
      // it's invalid on Windows.
      return "";
    } else if (filename.isDirectory()) {
      return "; however, a source directory of this name exists.  (Perhaps add "
          + "'exports_files([\""
          + targetName
          + "\"])' to "
          + getName()
          + "/BUILD, or define a "
          + "filegroup?)";
    } else if (filename.exists()) {
      return "; however, a source file of this name exists.  (Perhaps add "
          + "'exports_files([\""
          + targetName
          + "\"])' to "
          + getName()
          + "/BUILD?)";
    } else {
      String suggestedTarget = SpellChecker.suggest(targetName, targets.keySet());
      String targetSuggestion =
          suggestedTarget == null ? null : String.format("did you mean '%s'?", suggestedTarget);
      String blazeQuerySuggestion =
          String.format(
              "Tip: use `query \"%s:*\"` to see all the targets in that package",
              packageIdentifier.getDisplayForm(mainRepositoryMapping));
      return String.format(
          " (%s)", Joiner.on(" ").skipNulls().join(targetSuggestion, blazeQuerySuggestion));
    }
  }

  /**
   * Returns the default visibility for this package.
   */
  public RuleVisibility getDefaultVisibility() {
    return defaultVisibility;
  }

  /**
   * How to enforce visibility on <code>config_setting</code> See
   * {@link ConfigSettingVisibilityPolicy} for details.
   */
  public ConfigSettingVisibilityPolicy getConfigSettingVisibilityPolicy() {
    return configSettingVisibilityPolicy;
  }

  /**
   * Returns the default testonly value.
   */
  public Boolean getDefaultTestOnly() {
    return defaultTestOnly;
  }

  /**
   * Returns the default deprecation value.
   */
  public String getDefaultDeprecation() {
    return defaultDeprecation;
  }

  /** Gets the default header checking mode. */
  public String getDefaultHdrsCheck() {
    return defaultHdrsCheck != null ? defaultHdrsCheck : "strict";
  }

  /**
   * Returns whether the default header checking mode has been set or it is the
   * default value.
   */
  public boolean isDefaultHdrsCheckSet() {
    return defaultHdrsCheck != null;
  }

  public boolean isDefaultVisibilitySet() {
    return defaultVisibilitySet;
  }

  /** Gets the package metadata list for the default metadata declared by this package. */
  Set<Label> getDefaultPackageMetadata() {
    return defaultPackageMetadata;
  }

  /** Gets the parsed license object for the default license declared by this package. */
  License getDefaultLicense() {
    return defaultLicense;
  }

  /** Returns the parsed set of distributions declared as the default for this package. */
  Set<License.DistributionType> getDefaultDistribs() {
    return defaultDistributionSet;
  }

  /**
   * Returns the default value to use for a rule's {@link RuleClass#COMPATIBLE_ENVIRONMENT_ATTR}
   * attribute when not explicitly specified by the rule.
   */
  public Set<Label> getDefaultCompatibleWith() {
    return defaultCompatibleWith;
  }

  /**
   * Returns the default value to use for a rule's {@link RuleClass#RESTRICTED_ENVIRONMENT_ATTR}
   * attribute when not explicitly specified by the rule.
   */
  public Set<Label> getDefaultRestrictedTo() {
    return defaultRestrictedTo;
  }

  public ImmutableList<TargetPattern> getRegisteredExecutionPlatforms() {
    return registeredExecutionPlatforms;
  }

  public ImmutableList<TargetPattern> getRegisteredToolchains() {
    return registeredToolchains;
  }

  @Override
  public String toString() {
    return "Package("
        + getName()
        + ")="
        + (targets != null ? getTargets(Rule.class) : "initializing...");
  }

  /**
   * Dumps the package for debugging. Do not depend on the exact format/contents of this debugging
   * output.
   */
  public void dump(PrintStream out) {
    out.println("  Package " + getName() + " (" + filename.asPath() + ")");

    // Rules:
    out.println("    Rules");
    for (Rule rule : getTargets(Rule.class)) {
      out.println("      " + rule.getTargetKind() + " " + rule.getLabel());
      for (Attribute attr : rule.getAttributes()) {
        for (Object possibleValue : AggregatingAttributeMapper.of(rule)
            .visitAttribute(attr.getName(), attr.getType())) {
          out.println("        " + attr.getName() + " = " + possibleValue);
        }
      }
    }

    // Files:
    out.println("    Files");
    for (FileTarget file : getTargets(FileTarget.class)) {
      out.print("      " + file.getTargetKind() + " " + file.getLabel());
      if (file instanceof OutputFile) {
        out.println(" (generated by " + ((OutputFile) file).getGeneratingRule().getLabel() + ")");
      } else {
        out.println();
      }
    }
  }

  public static Builder newExternalPackageBuilder(
      PackageSettings helper,
      RootedPath workspacePath,
      String workspaceName,
      RepositoryMapping mainRepoMapping,
      StarlarkSemantics starlarkSemantics) {
    return new Builder(
            helper,
            LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
            workspaceName,
            /* associatedModuleName= */ Optional.empty(),
            /* associatedModuleVersion= */ Optional.empty(),
            starlarkSemantics.getBool(BuildLanguageOptions.INCOMPATIBLE_NO_IMPLICIT_FILE_EXPORT),
            mainRepoMapping,
            mainRepoMapping)
        .setFilename(workspacePath);
  }

  public static Builder newExternalPackageBuilderForBzlmod(
      RootedPath moduleFilePath,
      StarlarkSemantics starlarkSemantics,
      PackageIdentifier basePackageId,
      RepositoryMapping repoMapping) {
    return new Builder(
            DefaultPackageSettings.INSTANCE,
            basePackageId,
            DUMMY_WORKSPACE_NAME_FOR_BZLMOD_PACKAGES,
            /* associatedModuleName= */ Optional.empty(),
            /* associatedModuleVersion= */ Optional.empty(),
            starlarkSemantics.getBool(BuildLanguageOptions.INCOMPATIBLE_NO_IMPLICIT_FILE_EXPORT),
            repoMapping,
            // This mapping is *not* the main repository's mapping, but since it is only used to
            // construct a query command in an error message and the package built here can't be
            // seen by query, the particular value does not matter.
            RepositoryMapping.ALWAYS_FALLBACK)
        .setFilename(moduleFilePath);
  }

  /**
   * Returns an error {@link Event} with {@link Location} and {@link DetailedExitCode} properties.
   */
  public static Event error(Location location, String message, Code code) {
    Event error = Event.error(location, message);
    return error.withProperty(DetailedExitCode.class, createDetailedCode(message, code));
  }

  private static DetailedExitCode createDetailedCode(String errorMessage, Code code) {
    return DetailedExitCode.of(
        FailureDetail.newBuilder()
            .setMessage(errorMessage)
            .setPackageLoading(PackageLoading.newBuilder().setCode(code))
            .build());
  }

  /**
   * A builder for {@link Package} objects. Only intended to be used by {@link PackageFactory} and
   * {@link com.google.devtools.build.lib.skyframe.PackageFunction}.
   */
  public static class Builder {

    /** Defines configuration to control the runtime behavior of {@link Package}s. */
    public interface PackageSettings {
      /**
       * Returns whether or not extra detail should be added to {@link NoSuchTargetException}s
       * thrown from {@link #getTarget}. Useful for toning down verbosity in situations where it can
       * be less helpful.
       */
      boolean succinctTargetNotFoundErrors();

      /**
       * Reports whether to record the set of Modules loaded by this package, which enables richer
       * modes of blaze query.
       */
      boolean recordLoadedModules();
    }

    /** Default {@link PackageSettings}. */
    public static class DefaultPackageSettings implements PackageSettings {
      public static final DefaultPackageSettings INSTANCE = new DefaultPackageSettings();

      private DefaultPackageSettings() {}

      @Override
      public boolean succinctTargetNotFoundErrors() {
        return false;
      }

      @Override
      public boolean recordLoadedModules() {
        return true;
      }
    }

    /**
     * The output instance for this builder. Needs to be instantiated and
     * available with name info throughout initialization. All other settings
     * are applied during {@link #build}. See {@link Package#Package}
     * and {@link Package#finishInit} for details.
     */
    private final Package pkg;

    private final boolean noImplicitFileExport;

    // The map from each repository to that repository's remappings map.
    // This is only used in the //external package, it is an empty map for all other packages.
    private final HashMap<RepositoryName, HashMap<String, RepositoryName>>
        externalPackageRepositoryMappings = new HashMap<>();
    /**
     * The map of repository reassignments for BUILD packages loaded within external repositories.
     * It contains an entry from "@<main workspace name>" to "@" for packages within the main
     * workspace.
     */
    private final RepositoryMapping repositoryMapping;
    /**
     * The repository mapping of the main repository. This is only used to resolve user-friendly
     * apparent names from canonical repository names in error message arising from this package.
     */
    private final RepositoryMapping mainRepositoryMapping;
    /** Converts label literals to Label objects within this package. */
    private final LabelConverter labelConverter;

    private RootedPath filename = null;
    private Label buildFileLabel = null;
    private InputFile buildFile = null;
    // TreeMap so that the iteration order of variables is predictable. This is useful so that the
    // serialized representation is deterministic.
    private final TreeMap<String, String> makeEnv = new TreeMap<>();
    private RuleVisibility defaultVisibility = RuleVisibility.PRIVATE;
    private ConfigSettingVisibilityPolicy configSettingVisibilityPolicy;
    private boolean defaultVisibilitySet;
    private final List<String> features = new ArrayList<>();
    private final List<Event> events = Lists.newArrayList();
    private final List<Postable> posts = Lists.newArrayList();
    @Nullable private String ioExceptionMessage = null;
    @Nullable private IOException ioException = null;
    @Nullable private DetailedExitCode ioExceptionDetailedExitCode = null;
    private boolean containsErrors = false;
    // A package's FailureDetail field derives from its Builder's events. During package
    // deserialization, those events are unavailable, because those events aren't serialized [*].
    // Its FailureDetail value is serialized, however. During deserialization, that value is
    // assigned here, so that it can be assigned to the deserialized package.
    //
    // Likewise, during workspace part assembly, errors from parent parts should propagate to their
    // children.
    //
    // [*] Not in the context of the package, anyway. Skyframe values containing a package may
    // serialize events emitted during its construction/evaluation.
    @Nullable private FailureDetail failureDetailOverride = null;

    private ImmutableList<Label> defaultPackageMetadata = ImmutableList.of();
    private License defaultLicense = License.NO_LICENSE;
    private Set<License.DistributionType> defaultDistributionSet = License.DEFAULT_DISTRIB;

    // All targets added to the package. We use SnapshottableBiMap to help track insertion order of
    // Rule targets, for use by native.existing_rules().
    private BiMap<String, Target> targets =
        new SnapshottableBiMap<>(target -> target instanceof Rule);
    private final Map<Label, EnvironmentGroup> environmentGroups = new HashMap<>();

    /**
     * Stores labels for each rule so that we don't have to call the costly {@link Rule#getLabels}
     * twice (once for {@link #checkForInputOutputConflicts} and once for {@link #beforeBuild}).
     *
     * <p>Remains {@code null} when rules are added via {@link #addRuleUnchecked}, which occurs with
     * package deserialization. Set back to {@code null} after building.
     */
    @Nullable private Map<Rule, List<Label>> ruleLabels = null;

    private ImmutableList<Label> starlarkFileDependencies = ImmutableList.of();

    private final List<TargetPattern> registeredExecutionPlatforms = new ArrayList<>();
    private final List<TargetPattern> registeredToolchains = new ArrayList<>();

    /**
     * True iff the "package" function has already been called in this package.
     */
    private boolean packageFunctionUsed;

    /**
     * The collection of the prefixes of every output file. Maps every prefix to an output file
     * whose prefix it is.
     *
     * <p>This is needed to make the output file prefix conflict check be reasonably fast. However,
     * since it can potentially take a lot of memory and is useless after the package has been
     * loaded, it isn't passed to the package itself.
     */
    private final Map<String, OutputFile> outputFilePrefixes = new HashMap<>();

    private final Interner<ImmutableList<?>> listInterner = new ThreadCompatibleInterner<>();

    private ImmutableMap<Location, String> generatorMap = ImmutableMap.of();

    private final TestSuiteImplicitTestsAccumulator testSuiteImplicitTestsAccumulator =
        new TestSuiteImplicitTestsAccumulator();

    /** Returns the "generator_name" to use for a given call site location in a BUILD file. */
    @Nullable
    String getGeneratorNameByLocation(Location loc) {
      return generatorMap.get(loc);
    }

    /** Sets the package's map of "generator_name" values keyed by the location of the call site. */
    @CanIgnoreReturnValue
    public Builder setGeneratorMap(ImmutableMap<Location, String> map) {
      this.generatorMap = map;
      return this;
    }

    /**
     * Returns the value to use for {@code test_suite}s' {@code $implicit_tests} attribute, as-is,
     * when the {@code test_suite} doesn't specify an explicit, non-empty {@code tests} value. The
     * returned list is mutated by the package-building process - it may be observed to be empty or
     * incomplete before package loading is complete. When package loading is complete it will
     * contain the label of each non-manual test matching the provided tags in the package, in label
     * order.
     *
     * <p>This method <b>MUST</b> be called before the package is built - otherwise the requested
     * implicit tests won't be accumulated.
     */
    List<Label> getTestSuiteImplicitTestsRef(List<String> tags) {
      return testSuiteImplicitTestsAccumulator.getTestSuiteImplicitTestsRefForTags(tags);
    }

    @ThreadCompatible
    private static final class ThreadCompatibleInterner<T> implements Interner<T> {
      private final Map<T, T> interns = new HashMap<>();

      @Override
      public T intern(T sample) {
        T existing = interns.putIfAbsent(sample, sample);
        return firstNonNull(existing, sample);
      }
    }

    private boolean alreadyBuilt = false;

    Builder(
        PackageSettings packageSettings,
        PackageIdentifier id,
        String workspaceName,
        Optional<String> associatedModuleName,
        Optional<String> associatedModuleVersion,
        boolean noImplicitFileExport,
        RepositoryMapping repositoryMapping,
        RepositoryMapping mainRepositoryMapping) {
      this.pkg =
          new Package(
              id,
              workspaceName,
              associatedModuleName,
              associatedModuleVersion,
              packageSettings.succinctTargetNotFoundErrors());
      this.noImplicitFileExport = noImplicitFileExport;
      this.repositoryMapping = repositoryMapping;
      this.mainRepositoryMapping = mainRepositoryMapping;
      this.labelConverter = new LabelConverter(id, repositoryMapping);
      if (pkg.getName().startsWith("javatests/")) {
        setDefaultTestonly(true);
      }
    }

    PackageIdentifier getPackageIdentifier() {
      return pkg.getPackageIdentifier();
    }

    /**
     * Determine whether this package should contain build rules (returns {@code false}) or repo
     * rules (returns {@code true}).
     */
    boolean isRepoRulePackage() {
      return pkg.isRepoRulePackage();
    }

    String getPackageWorkspaceName() {
      return pkg.getWorkspaceName();
    }

    /**
     * Returns the name of the Bzlmod module associated with the repo this package is in. If this
     * package is not from a Bzlmod repo, this is empty. For repos generated by module extensions,
     * this is the name of the module hosting the extension.
     */
    Optional<String> getAssociatedModuleName() {
      return pkg.associatedModuleName;
    }

    /**
     * Returns the version of the Bzlmod module associated with the repo this package is in. If this
     * package is not from a Bzlmod repo, this is empty. For repos generated by module extensions,
     * this is the version of the module hosting the extension.
     */
    Optional<String> getAssociatedModuleVersion() {
      return pkg.associatedModuleVersion;
    }

    /**
     * Updates the externalPackageRepositoryMappings entry for {@code repoWithin}. Adds new entry
     * from {@code localName} to {@code mappedName} in {@code repoWithin}'s map.
     *
     * @param repoWithin the RepositoryName within which the mapping should apply
     * @param localName the name that actually appears in the WORKSPACE and BUILD files in the
     *     {@code repoWithin} repository
     * @param mappedName the RepositoryName by which localName should be referenced
     */
    @CanIgnoreReturnValue
    Builder addRepositoryMappingEntry(
        RepositoryName repoWithin, String localName, RepositoryName mappedName) {
      HashMap<String, RepositoryName> mapping =
          externalPackageRepositoryMappings.computeIfAbsent(
              repoWithin, (RepositoryName k) -> new HashMap<>());
      mapping.put(localName, mappedName);
      return this;
    }

    /** Adds all the mappings from a given {@link Package}. */
    @CanIgnoreReturnValue
    Builder addRepositoryMappings(Package aPackage) {
      ImmutableMap<RepositoryName, ImmutableMap<String, RepositoryName>> repositoryMappings =
          aPackage.externalPackageRepositoryMappings;
      for (Map.Entry<RepositoryName, ImmutableMap<String, RepositoryName>> repositoryName :
          repositoryMappings.entrySet()) {
        for (Map.Entry<String, RepositoryName> repositoryNameRepositoryNameEntry :
            repositoryName.getValue().entrySet()) {
          addRepositoryMappingEntry(
              repositoryName.getKey(),
              repositoryNameRepositoryNameEntry.getKey(),
              repositoryNameRepositoryNameEntry.getValue());
        }
      }
      return this;
    }

    public LabelConverter getLabelConverter() {
      return labelConverter;
    }

    Interner<ImmutableList<?>> getListInterner() {
      return listInterner;
    }

    /** Sets the name of this package's BUILD file. */
    @CanIgnoreReturnValue
    public Builder setFilename(RootedPath filename) {
      this.filename = filename;
      try {
        buildFileLabel = createLabel(filename.getRootRelativePath().getBaseName());
        addInputFile(buildFileLabel, Location.fromFile(filename.asPath().toString()));
      } catch (LabelSyntaxException e) {
        // This can't actually happen.
        throw new AssertionError("Package BUILD file has an illegal name: " + filename);
      }
      return this;
    }

    Label getBuildFileLabel() {
      return buildFileLabel;
    }

    /**
     * Return a read-only copy of the name mapping of external repositories for a given repository.
     * Reading that mapping directly from the builder allows to also take mappings into account that
     * are only discovered while constructing the external package (e.g., the mapping of the name of
     * the main workspace to the canonical main name '@').
     */
    RepositoryMapping getRepositoryMappingFor(RepositoryName name) {
      Map<String, RepositoryName> mapping = externalPackageRepositoryMappings.get(name);
      if (mapping == null) {
        return RepositoryMapping.ALWAYS_FALLBACK;
      } else {
        return RepositoryMapping.createAllowingFallback(mapping);
      }
    }

    RootedPath getFilename() {
      return filename;
    }

    /**
     * Returns {@link Postable}s accumulated while building the package.
     *
     * <p>Should retrieved and reported as close to after {@link #build()} or {@link #finishBuild()}
     * as possible - any earlier and the data may be incomplete.
     */
    public List<Postable> getPosts() {
      return posts;
    }

    /**
     * Returns {@link Event}s accumulated while building the package.
     *
     * <p>Should retrieved and reported as close to after {@link #build()} or {@link #finishBuild()}
     * as possible - any earlier and the data may be incomplete.
     */
    public List<Event> getEvents() {
      return events;
    }

    @CanIgnoreReturnValue
    Builder setMakeVariable(String name, String value) {
      this.makeEnv.put(name, value);
      return this;
    }

    /**
     * Sets the default visibility for this package. Called at most once per package from
     * PackageFactory.
     */
    @CanIgnoreReturnValue
    public Builder setDefaultVisibility(RuleVisibility visibility) {
      this.defaultVisibility = visibility;
      this.defaultVisibilitySet = true;
      return this;
    }

    /** Sets whether the default visibility is set in the BUILD file. */
    @CanIgnoreReturnValue
    public Builder setDefaultVisibilitySet(boolean defaultVisibilitySet) {
      this.defaultVisibilitySet = defaultVisibilitySet;
      return this;
    }

    /** Sets visibility enforcement policy for <code>config_setting</code>. */
    @CanIgnoreReturnValue
    public Builder setConfigSettingVisibilityPolicy(ConfigSettingVisibilityPolicy policy) {
      this.configSettingVisibilityPolicy = policy;
      return this;
    }

    /** Sets the default value of 'testonly'. Rule-level 'testonly' will override this. */
    @CanIgnoreReturnValue
    Builder setDefaultTestonly(boolean defaultTestonly) {
      pkg.setDefaultTestOnly(defaultTestonly);
      return this;
    }

    /** Sets the default value of 'deprecation'. Rule-level 'deprecation' will append to this. */
    @CanIgnoreReturnValue
    Builder setDefaultDeprecation(String defaultDeprecation) {
      pkg.setDefaultDeprecation(defaultDeprecation);
      return this;
    }

    /** Uses the workspace name from {@code //external} to set this package's workspace name. */
    @CanIgnoreReturnValue
    @VisibleForTesting
    public Builder setWorkspaceName(String workspaceName) {
      pkg.workspaceName = workspaceName;
      return this;
    }

    /**
     * Returns whether the "package" function has been called yet
     */
    boolean isPackageFunctionUsed() {
      return packageFunctionUsed;
    }

    void setPackageFunctionUsed() {
      packageFunctionUsed = true;
    }

    /** Sets the number of Starlark computation steps executed by this BUILD file. */
    void setComputationSteps(long n) {
      pkg.computationSteps = n;
    }

    /** Sets the load mapping for this package. */
    void setLoads(ImmutableMap<String, Module> loads) {
      pkg.loads = Preconditions.checkNotNull(loads);
    }

    /** Sets the default header checking mode. */
    @CanIgnoreReturnValue
    public Builder setDefaultHdrsCheck(String hdrsCheck) {
      // Note that this setting is propagated directly to the package because
      // other code needs the ability to read this info directly from the
      // under-construction package. See {@link Package#setDefaultHdrsCheck}.
      pkg.setDefaultHdrsCheck(hdrsCheck);
      return this;
    }

    @CanIgnoreReturnValue
    public Builder addFeatures(Iterable<String> features) {
      Iterables.addAll(this.features, features);
      return this;
    }

    Builder setIOException(IOException e, String message, DetailedExitCode detailedExitCode) {
      this.ioException = e;
      this.ioExceptionMessage = message;
      this.ioExceptionDetailedExitCode = detailedExitCode;
      return setContainsErrors();
    }

    /**
     * Declares that errors were encountering while loading this package. If called, {@link
     * #addEvent} or {@link #addEvents} should already have been called with an {@link Event} of
     * type {@link EventKind#ERROR} that includes a {@link FailureDetail}.
     */
    @CanIgnoreReturnValue
    public Builder setContainsErrors() {
      containsErrors = true;
      return this;
    }

    public boolean containsErrors() {
      return containsErrors;
    }

    @CanIgnoreReturnValue
    Builder addPosts(Iterable<Postable> posts) {
      for (Postable post : posts) {
        this.posts.add(post);
      }
      return this;
    }

    @CanIgnoreReturnValue
    Builder addEvents(Iterable<Event> events) {
      for (Event event : events) {
        addEvent(event);
      }
      return this;
    }

    @CanIgnoreReturnValue
    public Builder addEvent(Event event) {
      this.events.add(event);
      return this;
    }

    void setFailureDetailOverride(FailureDetail failureDetail) {
      failureDetailOverride = failureDetail;
    }

    @Nullable
    FailureDetail getFailureDetail() {
      if (failureDetailOverride != null) {
        return failureDetailOverride;
      }

      List<Event> undetailedEvents = null;
      for (Event event : this.events) {
        if (event.getKind() != EventKind.ERROR) {
          continue;
        }
        DetailedExitCode detailedExitCode = event.getProperty(DetailedExitCode.class);
        if (detailedExitCode != null && detailedExitCode.getFailureDetail() != null) {
          return detailedExitCode.getFailureDetail();
        }
        if (containsErrors) {
          if (undetailedEvents == null) {
            undetailedEvents = new ArrayList<>();
          }
          undetailedEvents.add(event);
        }
      }
      if (undetailedEvents != null) {
        BugReport.sendBugReport(
            new IllegalStateException("Package has undetailed error from " + undetailedEvents));
      }
      return null;
    }

    @CanIgnoreReturnValue
    public Builder setStarlarkFileDependencies(ImmutableList<Label> starlarkFileDependencies) {
      this.starlarkFileDependencies = starlarkFileDependencies;
      return this;
    }

    /**
     * Sets the default value to use for a rule's {@link RuleClass#APPLICABLE_LICENSES_ATTR}
     * attribute when not explicitly specified by the rule. Records a package error if any labels
     * are duplicated.
     */
    void setDefaultPackageMetadata(List<Label> licenses, String attrName, Location location) {
      if (hasDuplicateLabels(
          licenses, "package " + pkg.getName(), attrName, location, this::addEvent)) {
        setContainsErrors();
      }
      this.defaultPackageMetadata = ImmutableList.copyOf(licenses);
    }

    ImmutableList<Label> getDefaultPackageMetadata() {
      return defaultPackageMetadata;
    }

    /**
     * Sets the default license for this package.
     */
    void setDefaultLicense(License license) {
      this.defaultLicense = license;
    }

    License getDefaultLicense() {
      return defaultLicense;
    }

    /**
     * Initializes the default set of distributions for targets in this package.
     *
     * <p> TODO(bazel-team): (2011) consider moving the license & distribs info into Metadata--maybe
     * even in the Build language.
     */
    void setDefaultDistribs(Set<DistributionType> dists) {
      this.defaultDistributionSet = dists;
    }

    Set<DistributionType> getDefaultDistribs() {
      return defaultDistributionSet;
    }

    /**
     * Sets the default value to use for a rule's {@link RuleClass#COMPATIBLE_ENVIRONMENT_ATTR}
     * attribute when not explicitly specified by the rule. Records a package error if any labels
     * are duplicated.
     */
    void setDefaultCompatibleWith(List<Label> environments, String attrName, Location location) {
      if (hasDuplicateLabels(
          environments, "package " + pkg.getName(), attrName, location, this::addEvent)) {
        setContainsErrors();
      }
      pkg.setDefaultCompatibleWith(ImmutableSet.copyOf(environments));
    }

    /**
     * Sets the default value to use for a rule's {@link RuleClass#RESTRICTED_ENVIRONMENT_ATTR}
     * attribute when not explicitly specified by the rule. Records a package error if
     * any labels are duplicated.
     */
    void setDefaultRestrictedTo(List<Label> environments, String attrName, Location location) {
      if (hasDuplicateLabels(
          environments, "package " + pkg.getName(), attrName, location, this::addEvent)) {
        setContainsErrors();
      }

      pkg.setDefaultRestrictedTo(ImmutableSet.copyOf(environments));
    }

    /**
     * Creates a new {@link Rule} {@code r} where {@code r.getPackage()} is the {@link Package}
     * associated with this {@link Builder}.
     *
     * <p>The created {@link Rule} will have no output files and therefore will be in an invalid
     * state.
     */
    Rule createRule(
        Label label, RuleClass ruleClass, List<StarlarkThread.CallStackEntry> callstack) {
      return createRule(
          label,
          ruleClass,
          callstack.isEmpty() ? Location.BUILTIN : callstack.get(0).location,
          CallStack.compactInterior(callstack));
    }

    Rule createRule(
        Label label,
        RuleClass ruleClass,
        Location location,
        @Nullable CallStack.Node interiorCallStack) {
      return new Rule(pkg, label, ruleClass, location, interiorCallStack);
    }

    @Nullable
    Target getTarget(String name) {
      return targets.get(name);
    }

    /**
     * Replaces a target in the {@link Package} under construction with a new target with the same
     * name and belonging to the same package.
     *
     * <p>A hack needed for {@link WorkspaceFactoryHelper}.
     */
    void replaceTarget(Target newTarget) {
      Preconditions.checkArgument(
          targets.containsKey(newTarget.getName()),
          "No existing target with name '%s' in the targets map",
          newTarget.getName());
      Preconditions.checkArgument(
          newTarget.getPackage() == pkg, // pointer comparison since we're constructing `pkg`
          "Replacement target belongs to package '%s', expected '%s'",
          newTarget.getPackage(),
          pkg);
      Target oldTarget = targets.put(newTarget.getName(), newTarget);
      if (newTarget instanceof Rule && ruleLabels != null) {
        List<Label> ruleLabelsForOldTarget = ruleLabels.remove(oldTarget);
        if (ruleLabelsForOldTarget != null) {
          ruleLabels.put((Rule) newTarget, ruleLabelsForOldTarget);
        }
      }
    }

    public Set<Target> getTargets() {
      return Package.getTargets(targets);
    }

    /**
     * Returns a lightweight snapshot view of the names of all rule targets belonging to this
     * package at the time of this call.
     *
     * @throws IllegalStateException if this method is called after {@link #beforeBuild} has been
     *     called.
     */
    Map<String, Rule> getRulesSnapshotView() {
      if (targets instanceof SnapshottableBiMap<?, ?>) {
        return Maps.transformValues(
            ((SnapshottableBiMap<String, Target>) targets).getTrackedSnapshot(),
            target -> (Rule) target);
      } else {
        throw new IllegalStateException(
            "getRulesSnapshotView() cannot be used after beforeBuild() has been called");
      }
    }

    /**
     * Returns an {@link Iterable} of all the rule instance targets belonging to this package.
     *
     * <p>The returned {@link Iterable} will be deterministically ordered, in the order the rule
     * instance targets were instantiated.
     */
    private Iterable<Rule> getRules() {
      return Package.getTargets(targets, Rule.class);
    }

    /**
     * An input file name conflicts with an existing package member.
     */
    static class GeneratedLabelConflict extends NameConflictException {
      private GeneratedLabelConflict(String message) {
        super(message);
      }
    }

    /**
     * Creates an input file target in this package with the specified name.
     *
     * @param targetName name of the input file.  This must be a valid target
     *   name as defined by {@link
     *   com.google.devtools.build.lib.cmdline.LabelValidator#validateTargetName}.
     * @return the newly-created InputFile, or the old one if it already existed.
     * @throws GeneratedLabelConflict if the name was already taken by a Rule or
     *     an OutputFile target.
     * @throws IllegalArgumentException if the name is not a valid label
     */
    InputFile createInputFile(String targetName, Location location)
        throws GeneratedLabelConflict {
      Target existing = targets.get(targetName);
      if (existing == null) {
        try {
          return addInputFile(createLabel(targetName), location);
        } catch (LabelSyntaxException e) {
          throw new IllegalArgumentException(
              "FileTarget in package " + pkg.getName() + " has illegal name: " + targetName, e);
        }
      } else if (existing instanceof InputFile) {
        return (InputFile) existing; // idempotent
      } else {
        throw new GeneratedLabelConflict("generated label '//" + pkg.getName() + ":"
            + targetName + "' conflicts with existing "
            + existing.getTargetKind());
      }
    }

    /**
     * Sets the visibility and license for an input file. The input file must already exist as
     * a member of this package.
     * @throws IllegalArgumentException if the input file doesn't exist in this
     *     package's target map.
     */
    void setVisibilityAndLicense(InputFile inputFile, RuleVisibility visibility, License license) {
      String filename = inputFile.getName();
      Target cacheInstance = targets.get(filename);
      if (!(cacheInstance instanceof InputFile)) {
        throw new IllegalArgumentException("Can't set visibility for nonexistent FileTarget "
                                           + filename + " in package " + pkg.getName() + ".");
      }
      if (!((InputFile) cacheInstance).isVisibilitySpecified()
          || cacheInstance.getVisibility() != visibility
          || !Objects.equals(cacheInstance.getLicense(), license)) {
        targets.put(
            filename,
            new VisibilityLicenseSpecifiedInputFile(
                pkg, cacheInstance.getLabel(), cacheInstance.getLocation(), visibility, license));
      }
    }

    /**
     * Creates a label for a target inside this package.
     *
     * @throws LabelSyntaxException if the {@code targetName} is invalid
     */
    Label createLabel(String targetName) throws LabelSyntaxException {
      return Label.create(pkg.getPackageIdentifier(), targetName);
    }

    /** Adds a package group to the package. */
    void addPackageGroup(
        String name,
        Collection<String> packages,
        Collection<Label> includes,
        boolean allowPublicPrivate,
        boolean repoRootMeansCurrentRepo,
        EventHandler eventHandler,
        Location location)
        throws NameConflictException, LabelSyntaxException {
      PackageGroup group =
          new PackageGroup(
              createLabel(name),
              pkg,
              packages,
              includes,
              allowPublicPrivate,
              repoRootMeansCurrentRepo,
              eventHandler,
              location);
      Target existing = targets.get(group.getName());
      if (existing != null) {
        throw nameConflict(group, existing);
      }

      targets.put(group.getName(), group);

      if (group.containsErrors()) {
        setContainsErrors();
      }
    }

    /**
     * Returns true if any labels in the given list appear multiple times, reporting an appropriate
     * error message if so.
     *
     * <p>TODO(bazel-team): apply this to all build functions (maybe automatically?), possibly
     * integrate with RuleClass.checkForDuplicateLabels.
     */
    private static boolean hasDuplicateLabels(
        List<Label> labels,
        String owner,
        String attrName,
        Location location,
        EventHandler eventHandler) {
      Set<Label> dupes = CollectionUtils.duplicatedElementsOf(labels);
      for (Label dupe : dupes) {
        eventHandler.handle(
            error(
                location,
                String.format(
                    "label '%s' is duplicated in the '%s' list of '%s'", dupe, attrName, owner),
                Code.DUPLICATE_LABEL));
      }
      return !dupes.isEmpty();
    }

    /**
     * Adds an environment group to the package.
     */
    void addEnvironmentGroup(String name, List<Label> environments, List<Label> defaults,
        EventHandler eventHandler, Location location)
        throws NameConflictException, LabelSyntaxException {

      if (hasDuplicateLabels(environments, name, "environments", location, eventHandler)
          || hasDuplicateLabels(defaults, name, "defaults", location, eventHandler)) {
        setContainsErrors();
        return;
      }

      EnvironmentGroup group = new EnvironmentGroup(createLabel(name), pkg, environments,
          defaults, location);
      Target existing = targets.get(group.getName());
      if (existing != null) {
        throw nameConflict(group, existing);
      }

      targets.put(group.getName(), group);
      // Invariant: once group is inserted into targets, it must also:
      // (a) be inserted into environmentGroups, or
      // (b) have its group.processMemberEnvironments called.
      // Otherwise it will remain uninitialized,
      // causing crashes when it is later toString-ed.

      for (Event error : group.validateMembership()) {
        eventHandler.handle(error);
        setContainsErrors();
      }

      // For each declared environment, make sure it doesn't also belong to some other group.
      for (Label environment : group.getEnvironments()) {
        EnvironmentGroup otherGroup = environmentGroups.get(environment);
        if (otherGroup != null) {
          eventHandler.handle(
              error(
                  location,
                  String.format(
                      "environment %s belongs to both %s and %s",
                      environment, group.getLabel(), otherGroup.getLabel()),
                  Code.ENVIRONMENT_IN_MULTIPLE_GROUPS));
          setContainsErrors();
          // Ensure the orphan gets (trivially) initialized.
          group.processMemberEnvironments(ImmutableMap.of());
        } else {
          environmentGroups.put(environment, group);
        }
      }
    }

    /**
     * Same as {@link #addRule}, except with no name conflict checks.
     *
     * <p>Don't call this function unless you know what you're doing.
     */
    void addRuleUnchecked(Rule rule) {
      Preconditions.checkArgument(rule.getPackage() == pkg);
      // Now, modify the package:
      for (OutputFile outputFile : rule.getOutputFiles()) {
        targets.put(outputFile.getName(), outputFile);
        PathFragment outputFileFragment = PathFragment.create(outputFile.getName());
        int segmentCount = outputFileFragment.segmentCount();
        for (int i = 1; i < segmentCount; i++) {
          String prefix = outputFileFragment.subFragment(0, i).toString();
          outputFilePrefixes.putIfAbsent(prefix, outputFile);
        }
      }
      targets.put(rule.getName(), rule);
      if (rule.containsErrors()) {
        this.setContainsErrors();
      }
    }

    void addRule(Rule rule) throws NameConflictException {
      List<Label> labels = rule.getLabels();
      checkForConflicts(rule, labels);
      addRuleUnchecked(rule);
      if (ruleLabels == null) {
        ruleLabels = new HashMap<>();
      }
      ruleLabels.put(rule, labels);
    }

    void addRegisteredExecutionPlatforms(List<TargetPattern> platforms) {
      this.registeredExecutionPlatforms.addAll(platforms);
    }

    void addRegisteredToolchains(List<TargetPattern> toolchains) {
      this.registeredToolchains.addAll(toolchains);
    }

    @CanIgnoreReturnValue
    private Builder beforeBuild(boolean discoverAssumedInputFiles) throws NoSuchPackageException {
      Preconditions.checkNotNull(pkg);
      Preconditions.checkNotNull(filename);
      Preconditions.checkNotNull(buildFileLabel);
      Preconditions.checkNotNull(makeEnv);
      if (ioException != null) {
        throw new NoSuchPackageException(
            getPackageIdentifier(), ioExceptionMessage, ioException, ioExceptionDetailedExitCode);
      }

      // SnapshottableBiMap does not allow removing targets (in order to efficiently track rule
      // insertion order). However, we *do* need to support removal of targets in
      // PackageFunction.handleLabelsCrossingSubpackagesAndPropagateInconsistentFilesystemExceptions
      // which is called *between* calls to beforeBuild and finishBuild. We thus repoint the targets
      // map to the SnapshottableBiMap's underlying bimap and thus stop tracking insertion order.
      // After this point, snapshots of targets should no longer be used, and any further
      // getRulesSnapshotView calls will throw.
      if (targets instanceof SnapshottableBiMap<?, ?>) {
        targets = ((SnapshottableBiMap<String, Target>) targets).getUnderlyingBiMap();
      }

      // We create the original BUILD InputFile when the package filename is set; however, the
      // visibility may be overridden with an exports_files directive, so we need to obtain the
      // current instance here.
      buildFile = (InputFile) Preconditions.checkNotNull(targets.get(buildFileLabel.getName()));

      // Clear tests before discovering them again in order to keep this method idempotent -
      // otherwise we may double-count tests if we're called twice due to a skyframe restart, etc.
      testSuiteImplicitTestsAccumulator.clearAccumulatedTests();

      Map<String, InputFile> newInputFiles = new HashMap<>();
      for (Rule rule : getRules()) {
        if (discoverAssumedInputFiles) {
          // All labels mentioned by a rule that refer to an unknown target in the current package
          // are assumed to be InputFiles, so let's create them. We add them to a temporary map
          // to avoid concurrent modification to this.targets while iterating (via getRules()).
          List<Label> labels = ruleLabels != null ? ruleLabels.get(rule) : rule.getLabels();
          for (Label label : labels) {
            if (label.getPackageIdentifier().equals(pkg.getPackageIdentifier())
                && !targets.containsKey(label.getName())
                && !newInputFiles.containsKey(label.getName())) {
              Location loc = rule.getLocation();
              newInputFiles.put(
                  label.getName(),
                  noImplicitFileExport
                      ? new PrivateVisibilityInputFile(pkg, label, loc)
                      : new InputFile(pkg, label, loc));
            }
          }
        }

        testSuiteImplicitTestsAccumulator.processRule(rule);
      }

      // Make sure all accumulated values are sorted for determinism.
      testSuiteImplicitTestsAccumulator.sortTests();

      for (InputFile file : newInputFiles.values()) {
        addInputFile(file);
      }

      return this;
    }

    /** Intended for use by {@link com.google.devtools.build.lib.skyframe.PackageFunction} only. */
    public Builder buildPartial() throws NoSuchPackageException {
      if (alreadyBuilt) {
        return this;
      }
      return beforeBuild(/*discoverAssumedInputFiles=*/ true);
    }

    /** Intended for use by {@link com.google.devtools.build.lib.skyframe.PackageFunction} only. */
    public Package finishBuild() {
      if (alreadyBuilt) {
        return pkg;
      }

      // Freeze targets and distributions.
      for (Rule rule : getRules()) {
        rule.freeze();
      }
      ruleLabels = null;
      targets = Maps.unmodifiableBiMap(targets);
      defaultDistributionSet =
          Collections.unmodifiableSet(defaultDistributionSet);

      // Now all targets have been loaded, so we validate the group's member environments.
      for (EnvironmentGroup envGroup : ImmutableSet.copyOf(environmentGroups.values())) {
        Collection<Event> errors = envGroup.processMemberEnvironments(targets);
        if (!errors.isEmpty()) {
          addEvents(errors);
          setContainsErrors();
        }
      }

      // Build the package.
      pkg.finishInit(this);
      alreadyBuilt = true;
      return pkg;
    }

    public Package build() throws NoSuchPackageException {
      return build(/*discoverAssumedInputFiles=*/ true);
    }

    /**
     * Build the package, optionally adding any labels in the package not already associated with a
     * target as an input file.
     */
    Package build(boolean discoverAssumedInputFiles) throws NoSuchPackageException {
      if (alreadyBuilt) {
        return pkg;
      }
      beforeBuild(discoverAssumedInputFiles);
      return finishBuild();
    }

    private InputFile addInputFile(Label label, Location location) {
      return addInputFile(new InputFile(pkg, label, location));
    }

    private InputFile addInputFile(InputFile inputFile) {
      Target prev = targets.put(inputFile.getLabel().getName(), inputFile);
      Preconditions.checkState(prev == null);
      return inputFile;
    }

    /**
     * Precondition check for addRule. We must maintain these invariants of the package:
     *
     * <ul>
     *   <li>Each name refers to at most one target.
     *   <li>No rule with errors is inserted into the package.
     *   <li>The generating rule of every output file in the package must itself be in the package.
     * </ul>
     */
    private void checkForConflicts(Rule rule, List<Label> labels) throws NameConflictException {
      String name = rule.getName();
      Target existing = targets.get(name);
      if (existing != null) {
        throw nameConflict(rule, existing);
      }

      List<OutputFile> outputFiles = rule.getOutputFiles();
      Map<String, OutputFile> outputFilesByName =
          Maps.newHashMapWithExpectedSize(outputFiles.size());

      for (OutputFile outputFile : outputFiles) {
        String outputFileName = outputFile.getName();
        if (outputFilesByName.put(outputFileName, outputFile) != null) {
          throw duplicateOutputFile(outputFile, outputFile); // Duplicate within a single rule.
        }
        existing = targets.get(outputFileName);
        if (existing != null) {
          throw duplicateOutputFile(outputFile, existing);
        }

        // Check if this output file is the prefix of an already existing one.
        if (outputFilePrefixes.containsKey(outputFileName)) {
          throw conflictingOutputFile(outputFile, outputFilePrefixes.get(outputFileName));
        }

        // Check if a prefix of this output file matches an already existing one.
        PathFragment outputFileFragment = PathFragment.create(outputFileName);
        int segmentCount = outputFileFragment.segmentCount();
        for (int i = 1; i < segmentCount; i++) {
          String prefix = outputFileFragment.subFragment(0, i).toString();
          if (outputFilesByName.containsKey(prefix)) {
            throw conflictingOutputFile(outputFile, outputFilesByName.get(prefix));
          }
          if (targets.get(prefix) instanceof OutputFile) {
            throw conflictingOutputFile(outputFile, (OutputFile) targets.get(prefix));
          }

          outputFilePrefixes.putIfAbsent(prefix, outputFile);
        }
      }

      checkForInputOutputConflicts(rule, labels, outputFilesByName.keySet());
    }

    /**
     * A utility method that checks for conflicts between input file names and output file names for
     * a rule from a build file.
     *
     * @param rule the rule whose inputs and outputs are to be checked for conflicts.
     * @param labels the rules {@linkplain Rule#getLabels labels}.
     * @param outputFiles a set containing the names of output files to be generated by the rule.
     * @throws NameConflictException if a conflict is found.
     */
    private static void checkForInputOutputConflicts(
        Rule rule, List<Label> labels, Set<String> outputFiles) throws NameConflictException {
      PackageIdentifier packageIdentifier = rule.getLabel().getPackageIdentifier();
      for (Label inputLabel : labels) {
        if (packageIdentifier.equals(inputLabel.getPackageIdentifier())
            && outputFiles.contains(inputLabel.getName())) {
          throw inputOutputNameConflict(rule, inputLabel.getName());
        }
      }
    }

    /** An output file conflicts with another output file or the BUILD file. */
    private static NameConflictException duplicateOutputFile(
        OutputFile duplicate, Target existing) {
      return new NameConflictException(duplicate.getTargetKind() + " '" + duplicate.getName()
          + "' in rule '" + duplicate.getGeneratingRule().getName() + "' "
          + conflictsWith(existing));
    }

    /** The package contains two targets with the same name. */
    private static NameConflictException nameConflict(Target duplicate, Target existing) {
      return new NameConflictException(duplicate.getTargetKind() + " '" + duplicate.getName()
          + "' in package '" + duplicate.getLabel().getPackageName() + "' "
          + conflictsWith(existing));
    }

    /** A a rule has a input/output name conflict. */
    private static NameConflictException inputOutputNameConflict(
        Rule rule, String conflictingName) {
      return new NameConflictException("rule '" + rule.getName() + "' has file '"
          + conflictingName + "' as both an input and an output");
    }

    private static NameConflictException conflictingOutputFile(
        OutputFile added, OutputFile existing) {
      if (added.getGeneratingRule() == existing.getGeneratingRule()) {
        return new NameConflictException(String.format(
            "rule '%s' has conflicting output files '%s' and '%s'", added.getGeneratingRule()
                .getName(), added.getName(), existing.getName()));
      } else {
        return new NameConflictException(String.format(
            "output file '%s' of rule '%s' conflicts with output file '%s' of rule '%s'", added
                .getName(), added.getGeneratingRule().getName(), existing.getName(), existing
                .getGeneratingRule().getName()));
      }
    }

    /**
     * Utility function for generating exception messages.
     */
    private static String conflictsWith(Target target) {
      String message = "conflicts with existing ";
      if (target instanceof OutputFile) {
        message +=
            "generated file from rule '"
                + ((OutputFile) target).getGeneratingRule().getName()
                + "'";
      } else {
        message += target.getTargetKind();
      }
      return message + ", defined at " + target.getLocation();
    }
  }

  /** Package codec implementation. */
  @VisibleForTesting
  static final class PackageCodec implements ObjectCodec<Package> {
    @Override
    public Class<Package> getEncodedClass() {
      return Package.class;
    }

    @Override
    public void serialize(
        SerializationContext context,
        Package input,
        CodedOutputStream codedOut)
        throws IOException, SerializationException {
      context.checkClassExplicitlyAllowed(Package.class, input);
      PackageCodecDependencies codecDeps = context.getDependency(PackageCodecDependencies.class);
      codecDeps.getPackageSerializer().serialize(context, input, codedOut);
    }

    @Override
    public Package deserialize(
        DeserializationContext context,
        CodedInputStream codedIn)
        throws SerializationException, IOException {
      PackageCodecDependencies codecDeps = context.getDependency(PackageCodecDependencies.class);
      return codecDeps.getPackageSerializer().deserialize(context, codedIn);
    }
  }
}