// 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.skylark;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.MutableActionGraph.ActionConflictException;
import com.google.devtools.build.lib.analysis.ActionsProvider;
import com.google.devtools.build.lib.analysis.ConfiguredTarget;
import com.google.devtools.build.lib.analysis.DefaultInfo;
import com.google.devtools.build.lib.analysis.RuleConfiguredTargetBuilder;
import com.google.devtools.build.lib.analysis.RuleContext;
import com.google.devtools.build.lib.analysis.Runfiles;
import com.google.devtools.build.lib.analysis.RunfilesProvider;
import com.google.devtools.build.lib.analysis.RunfilesSupport;
import com.google.devtools.build.lib.analysis.StarlarkProviderValidationUtil;
import com.google.devtools.build.lib.analysis.Whitelist;
import com.google.devtools.build.lib.analysis.test.CoverageCommon;
import com.google.devtools.build.lib.analysis.test.InstrumentedFilesInfo;
import com.google.devtools.build.lib.collect.nestedset.Depset;
import com.google.devtools.build.lib.collect.nestedset.NestedSet;
import com.google.devtools.build.lib.collect.nestedset.NestedSet.NestedSetDepthException;
import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
import com.google.devtools.build.lib.events.Event;
import com.google.devtools.build.lib.packages.AdvertisedProviderSet;
import com.google.devtools.build.lib.packages.BazelStarlarkContext;
import com.google.devtools.build.lib.packages.FunctionSplitTransitionWhitelist;
import com.google.devtools.build.lib.packages.Info;
import com.google.devtools.build.lib.packages.NativeProvider;
import com.google.devtools.build.lib.packages.Provider;
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.SkylarkInfo;
import com.google.devtools.build.lib.packages.StarlarkProviderIdentifier;
import com.google.devtools.build.lib.packages.StructImpl;
import com.google.devtools.build.lib.packages.StructProvider;
import com.google.devtools.build.lib.packages.TargetUtils;
import com.google.devtools.build.lib.packages.Type;
import com.google.devtools.build.lib.syntax.Dict;
import com.google.devtools.build.lib.syntax.EvalException;
import com.google.devtools.build.lib.syntax.EvalExceptionWithStackTrace;
import com.google.devtools.build.lib.syntax.Location;
import com.google.devtools.build.lib.syntax.Mutability;
import com.google.devtools.build.lib.syntax.Sequence;
import com.google.devtools.build.lib.syntax.Starlark;
import com.google.devtools.build.lib.syntax.StarlarkCallable;
import com.google.devtools.build.lib.syntax.StarlarkSemantics;
import com.google.devtools.build.lib.syntax.StarlarkThread;
import com.google.devtools.build.lib.syntax.StarlarkValue;
import com.google.devtools.build.lib.vfs.PathFragment;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import javax.annotation.Nullable;

/**
 * A helper class to build Rule Configured Targets via runtime loaded rule implementations defined
 * using the Starlark Build Extension Language.
 */
public final class SkylarkRuleConfiguredTargetUtil {

  private SkylarkRuleConfiguredTargetUtil() {}

  private static final ImmutableSet<String> DEFAULT_PROVIDER_FIELDS =
      ImmutableSet.of("files", "runfiles", "data_runfiles", "default_runfiles", "executable");

  /**
   * Create a Rule Configured Target from the ruleContext and the ruleImplementation. Returns null
   * if there were errors during target creation.
   */
  @Nullable
  public static ConfiguredTarget buildRule(
      RuleContext ruleContext,
      AdvertisedProviderSet advertisedProviders,
      StarlarkCallable ruleImplementation,
      Location location,
      StarlarkSemantics starlarkSemantics,
      String toolsRepository)
      throws InterruptedException, RuleErrorException, ActionConflictException {
    String expectFailure = ruleContext.attributes().get("expect_failure", Type.STRING);
    SkylarkRuleContext skylarkRuleContext = null;
    try (Mutability mutability = Mutability.create("configured target")) {
      skylarkRuleContext = new SkylarkRuleContext(ruleContext, null, starlarkSemantics);
      StarlarkThread thread =
          StarlarkThread.builder(mutability)
              .setSemantics(starlarkSemantics)
              .build();
      thread.setPrintHandler(
          Event.makeDebugPrintHandler(ruleContext.getAnalysisEnvironment().getEventHandler()));

      new BazelStarlarkContext(
              BazelStarlarkContext.Phase.ANALYSIS,
              toolsRepository,
              /*fragmentNameToClass=*/ null,
              ruleContext.getTarget().getPackage().getRepositoryMapping(),
              ruleContext.getSymbolGenerator(),
              ruleContext.getLabel(),
              /*transitiveDigest=*/ null)
          .storeInThread(thread);

      RuleClass ruleClass = ruleContext.getRule().getRuleClassObject();
      if (ruleClass.getRuleClassType().equals(RuleClass.Builder.RuleClassType.WORKSPACE)) {
        ruleContext.ruleError(
            "Found reference to a workspace rule in a context where a build"
                + " rule was expected; probably a reference to a target in that external"
                + " repository, properly specified as @reponame//path/to/package:target,"
                + " should have been specified by the requesting rule.");
        return null;
      }
      if (ruleClass.hasFunctionTransitionWhitelist()
          && !Whitelist.isAvailableBasedOnRuleLocation(
              ruleContext, FunctionSplitTransitionWhitelist.WHITELIST_NAME)) {
        if (!Whitelist.isAvailable(ruleContext, FunctionSplitTransitionWhitelist.WHITELIST_NAME)) {
          ruleContext.ruleError("Non-whitelisted use of Starlark transition");
        }
      }

      Object target =
          Starlark.call(
              thread,
              ruleImplementation,
              /*args=*/ ImmutableList.of(skylarkRuleContext),
              /*kwargs=*/ ImmutableMap.of());

      if (ruleContext.hasErrors()) {
        return null;
      } else if (!(target instanceof Info)
          && target != Starlark.NONE
          && !(target instanceof Iterable)) {
        ruleContext.ruleError(
            String.format(
                "Rule should return a struct or a list, but got %s", Starlark.type(target)));
        return null;
      } else if (!expectFailure.isEmpty()) {
        ruleContext.ruleError("Expected failure not found: " + expectFailure);
        return null;
      }
      ConfiguredTarget configuredTarget = createTarget(skylarkRuleContext, target);
      if (configuredTarget != null) {
        // If there was error creating the ConfiguredTarget, no further validation is needed.
        // Null will be returned and the errors thus reported.
        StarlarkProviderValidationUtil.validateArtifacts(ruleContext);
        checkDeclaredProviders(configuredTarget, advertisedProviders, location);
      }
      return configuredTarget;
    } catch (EvalException e) {
      addRuleToStackTrace(e, ruleContext.getRule(), ruleImplementation);
      // If the error was expected, return an empty target.
      if (!expectFailure.isEmpty() && getMessageWithoutStackTrace(e).matches(expectFailure)) {
        return new RuleConfiguredTargetBuilder(ruleContext)
            .add(RunfilesProvider.class, RunfilesProvider.EMPTY)
            .build();
      }
      ruleContext.ruleError("\n" + e.print());
      return null;
    } finally {
      if (skylarkRuleContext != null) {
        skylarkRuleContext.nullify();
      }
    }
  }

  private static void checkDeclaredProviders(
      ConfiguredTarget configuredTarget, AdvertisedProviderSet advertisedProviders, Location loc)
      throws EvalException {
    for (StarlarkProviderIdentifier providerId : advertisedProviders.getSkylarkProviders()) {
      if (configuredTarget.get(providerId) == null) {
        throw new EvalException(
            loc,
            String.format(
                "rule advertised the '%s' provider, but this provider was not among those returned",
                providerId.toString()));
      }
    }
  }

  /** Adds the given rule to the stack trace of the exception (if there is one). */
  private static void addRuleToStackTrace(EvalException ex, Rule rule, StarlarkCallable ruleImpl) {
    if (ex instanceof EvalExceptionWithStackTrace) {
      ((EvalExceptionWithStackTrace) ex)
          .registerPhantomCall(
              String.format("%s(name = '%s')", rule.getRuleClass(), rule.getName()),
              rule.getLocation(),
              ruleImpl);
    }
  }

  /**
   * Returns the message of the given exception after removing the stack trace, if present.
   */
  private static String getMessageWithoutStackTrace(EvalException ex) {
    if (ex instanceof EvalExceptionWithStackTrace) {
      return ((EvalExceptionWithStackTrace) ex).getOriginalMessage();
    }
    return ex.getMessage();
  }

  @Nullable
  private static ConfiguredTarget createTarget(SkylarkRuleContext context, Object target)
      throws EvalException, RuleErrorException, ActionConflictException {
    RuleConfiguredTargetBuilder builder = new RuleConfiguredTargetBuilder(
        context.getRuleContext());
    // Set the default files to build.

    Location loc =
        context.getRuleContext()
            .getRule()
            .getRuleClassObject()
            .getConfiguredTargetFunction()
            .getLocation();

    // TODO(adonovan): clean up addProviders' error handling,
    // reporting provider validity errors through ruleError
    // where possible. This allows for multiple events, with independent
    // locations, even for the same root cause.
    // EvalException is the wrong exception for createTarget to throw
    // since it is neither called by Starlark nor does it call Starlark.
    //
    // In the meantime, ensure that any EvalException has a location.
    try {
      addProviders(context, builder, target, loc);
    } catch (EvalException ex) {
      if (ex.getLocation() == null) {
        // Prefer target struct's creation location in error messages.
        if (target instanceof Info) {
          loc = ((Info) target).getCreationLoc();
        }
        ex = new EvalException(loc, ex.getMessage());
      }
      throw ex;
    }

    try {
      return builder.build();
    } catch (IllegalArgumentException e) {
      throw new EvalException(loc, e.getMessage());
    }
  }

  private static void addOutputGroups(Object outputGroups, RuleConfiguredTargetBuilder builder)
      throws EvalException {
    for (Map.Entry<String, StarlarkValue> entry :
        Dict.cast(outputGroups, String.class, StarlarkValue.class, "output_groups").entrySet()) {
      String outputGroup = entry.getKey();
      NestedSet<Artifact> artifacts = convertToOutputGroupValue(outputGroup, entry.getValue());
      builder.addOutputGroup(outputGroup, artifacts);
    }
  }

  private static void addInstrumentedFiles(
      StructImpl insStruct, RuleContext ruleContext, RuleConfiguredTargetBuilder builder)
      throws EvalException {
    List<String> extensions = null;
    if (insStruct.getFieldNames().contains("extensions")) {
      extensions = Sequence.cast(insStruct.getValue("extensions"), String.class, "extensions");
    }

    List<String> dependencyAttributes = Collections.emptyList();
    if (insStruct.getFieldNames().contains("dependency_attributes")) {
      dependencyAttributes =
          Sequence.cast(
              insStruct.getValue("dependency_attributes"), String.class, "dependency_attributes");
    }

    List<String> sourceAttributes = Collections.emptyList();
    if (insStruct.getFieldNames().contains("source_attributes")) {
      sourceAttributes =
          Sequence.cast(insStruct.getValue("source_attributes"), String.class, "source_attributes");
    }

    InstrumentedFilesInfo instrumentedFilesProvider =
        CoverageCommon.createInstrumentedFilesInfo(
            ruleContext,
            sourceAttributes,
            dependencyAttributes,
            extensions);
    builder.addNativeDeclaredProvider(instrumentedFilesProvider);
  }

  public static NestedSet<Artifact> convertToOutputGroupValue(String outputGroup, Object objects)
      throws EvalException {
    // regrettable preemptive allocation of error message
    String what = "output group '" + outputGroup + "'";
    return objects instanceof Sequence
        ? NestedSetBuilder.<Artifact>stableOrder()
            .addAll(Sequence.cast(objects, Artifact.class, what))
            .build()
        : Depset.cast(objects, Artifact.class, what);
  }

  private static void addProviders(
      SkylarkRuleContext context, RuleConfiguredTargetBuilder builder, Object target, Location loc)
      throws EvalException {

    StructImpl oldStyleProviders =
        SkylarkInfo.create(StructProvider.STRUCT, ImmutableMap.of(), loc);
    Map<Provider.Key, Info> declaredProviders = new LinkedHashMap<>();

    if (target instanceof Info) {
      // Either an old-style struct or a single declared provider (not in a list)
      Info info = (Info) target;
      // Use the creation location of this struct as a better reference in error messages
      loc = info.getCreationLoc();
      if (getProviderKey(loc, info).equals(StructProvider.STRUCT.getKey())) {

        if (context.getSkylarkSemantics().incompatibleDisallowStructProviderSyntax()) {
          throw Starlark.errorf(
              "Returning a struct from a rule implementation function is deprecated and will "
                  + "be removed soon. It may be temporarily re-enabled by setting "
                  + "--incompatible_disallow_struct_provider_syntax=false . See "
                  + "https://github.com/bazelbuild/bazel/issues/7347 for details.");
        }

        // Old-style struct, but it may contain declared providers
        StructImpl struct = (StructImpl) target;
        oldStyleProviders = struct;

        Object providersField = struct.getValue("providers");
        if (providersField != null) {
          for (Info provider : Sequence.cast(providersField, Info.class, "providers")) {
            Provider.Key providerKey = getProviderKey(loc, provider);
            if (declaredProviders.put(providerKey, provider) != null) {
              context
                  .getRuleContext()
                  .ruleError("Multiple conflicting returned providers with key " + providerKey);
            }
          }
        }
      } else {
        Provider.Key providerKey = getProviderKey(loc, info);
        // Single declared provider
        declaredProviders.put(providerKey, info);
      }
    } else if (target instanceof Sequence) {
      // Sequence of declared providers
      for (Info provider :
          Sequence.cast(target, Info.class, "result of rule implementation function")) {
        Provider.Key providerKey = getProviderKey(loc, provider);
        if (declaredProviders.put(providerKey, provider) != null) {
          context
              .getRuleContext()
              .ruleError("Multiple conflicting returned providers with key " + providerKey);
        }
      }
    }

    boolean defaultProviderProvidedExplicitly = false;

    for (Info declaredProvider : declaredProviders.values()) {
      if (getProviderKey(loc, declaredProvider).equals(DefaultInfo.PROVIDER.getKey())) {
        parseDefaultProviderFields((DefaultInfo) declaredProvider, context, builder);
        defaultProviderProvidedExplicitly = true;
      } else {
        builder.addSkylarkDeclaredProvider(declaredProvider);
      }
    }

    if (!defaultProviderProvidedExplicitly) {
      parseDefaultProviderFields(oldStyleProviders, context, builder);
    }

    for (String field : oldStyleProviders.getFieldNames()) {
      if (DEFAULT_PROVIDER_FIELDS.contains(field)) {
        // These fields have already been parsed above.
        // If a default provider has been provided explicitly then it's an error that they also
        // occur here.
        if (defaultProviderProvidedExplicitly) {
          throw new EvalException(
              loc,
              "Provider '"
                  + field
                  + "' should be specified in DefaultInfo if it's provided explicitly.");
        }
      } else if (field.equals("output_groups")) {
        addOutputGroups(oldStyleProviders.getValue(field), builder);
      } else if (field.equals("instrumented_files")) {
        addInstrumentedFiles(
            oldStyleProviders.getValue("instrumented_files", StructImpl.class),
            context.getRuleContext(),
            builder);
      } else if (!field.equals("providers")) { // "providers" already handled above.
        addProviderFromLegacySyntax(
            builder, oldStyleProviders, field, oldStyleProviders.getValue(field));
      }
    }
  }

  @SuppressWarnings("deprecation") // For legacy migrations
  private static void addProviderFromLegacySyntax(
      RuleConfiguredTargetBuilder builder,
      StructImpl oldStyleProviders,
      String fieldName,
      Object value)
      throws EvalException {
    builder.addSkylarkTransitiveInfo(fieldName, value);

    if (value instanceof Info) {
      Info info = (Info) value;

      // To facilitate migration off legacy provider syntax, implicitly set the modern provider key
      // and the canonical legacy provider key if applicable.
      if (shouldAddWithModernKey(builder, oldStyleProviders, fieldName, info)) {
        builder.addNativeDeclaredProvider(info);
      }

      if (info.getProvider() instanceof NativeProvider.WithLegacySkylarkName) {
        NativeProvider.WithLegacySkylarkName providerWithLegacyName =
            (NativeProvider.WithLegacySkylarkName) info.getProvider();
        if (shouldAddWithLegacyKey(oldStyleProviders, providerWithLegacyName)) {
          builder.addSkylarkTransitiveInfo(providerWithLegacyName.getSkylarkName(), info);
        }
      }
    }
  }

  @SuppressWarnings("deprecation") // For legacy migrations
  private static boolean shouldAddWithModernKey(
      RuleConfiguredTargetBuilder builder,
      StructImpl oldStyleProviders,
      String fieldName,
      Info info)
      throws EvalException {
    // If the modern key is already set, do nothing.
    if (builder.containsProviderKey(info.getProvider().getKey())) {
      return false;
    }
    if (info.getProvider() instanceof NativeProvider.WithLegacySkylarkName) {
      String canonicalLegacyKey =
          ((NativeProvider.WithLegacySkylarkName) info.getProvider()).getSkylarkName();
      // Add info using its modern key if it was specified using its canonical legacy key, or
      // if no provider was used using that canonical legacy key.
      return fieldName.equals(canonicalLegacyKey)
          || oldStyleProviders.getValue(canonicalLegacyKey) == null;
    } else {
      return true;
    }
  }

  @SuppressWarnings("deprecation") // For legacy migrations
  private static boolean shouldAddWithLegacyKey(
      StructImpl oldStyleProviders, NativeProvider.WithLegacySkylarkName provider)
      throws EvalException {
    String canonicalLegacyKey = provider.getSkylarkName();
    // Add info using its canonical legacy key if no provider was specified using that canonical
    // legacy key.
    return oldStyleProviders.getValue(canonicalLegacyKey) == null;
  }

  /**
   * Returns the provider key from an info object.
   *
   * @throws EvalException if the provider for this info object has not been exported, which can
   *     occur if the provider was declared in a non-global scope (for example a rule implementation
   *     function)
   */
  private static Provider.Key getProviderKey(Location loc, Info infoObject) throws EvalException {
    if (!infoObject.getProvider().isExported()) {
      throw new EvalException(
          loc,
          "cannot return a non-exported provider instance from a "
              + "rule implementation function. provider defined at "
              + infoObject.getProvider().getLocation()
              + " must be defined outside of a function scope.");
    }
    return infoObject.getProvider().getKey();
  }

  /**
   * Parses fields of (not necessarily a default) provider. If it is an actual default provider,
   * throws an {@link EvalException} if there are unknown fields.
   */
  private static void parseDefaultProviderFields(
      StructImpl provider, SkylarkRuleContext context, RuleConfiguredTargetBuilder builder)
      throws EvalException {
    Depset files = null;
    Runfiles statelessRunfiles = null;
    Runfiles dataRunfiles = null;
    Runfiles defaultRunfiles = null;
    Artifact executable = null;

    Location loc = provider.getCreationLoc();

    if (getProviderKey(loc, provider).equals(DefaultInfo.PROVIDER.getKey())) {
      DefaultInfo defaultInfo = (DefaultInfo) provider;

      files = defaultInfo.getFiles();
      statelessRunfiles = defaultInfo.getStatelessRunfiles();
      dataRunfiles = defaultInfo.getDataRunfiles();
      defaultRunfiles = defaultInfo.getDefaultRunfiles();
      executable = defaultInfo.getExecutable();

    } else {
      // Rule implementations aren't required to return default-info fields via a DefaultInfo
      // provider. They can return them as fields on the returned struct. For example,
      // 'return struct(executable = foo)' instead of 'return DefaultInfo(executable = foo)'.
      // TODO(cparsons): Look into deprecating this option.
      for (String field : provider.getFieldNames()) {
        if (field.equals("files")) {
          Object x = provider.getValue("files");
          Depset.cast(x, Artifact.class, "files"); // may throw exception
          files = (Depset) x;
        } else if (field.equals("runfiles")) {
          statelessRunfiles = provider.getValue("runfiles", Runfiles.class);
        } else if (field.equals("data_runfiles")) {
          dataRunfiles = provider.getValue("data_runfiles", Runfiles.class);
        } else if (field.equals("default_runfiles")) {
          defaultRunfiles = provider.getValue("default_runfiles", Runfiles.class);
        } else if (field.equals("executable") && provider.getValue("executable") != null) {
          executable = provider.getValue("executable", Artifact.class);
        }
      }

      if ((statelessRunfiles != null) && (dataRunfiles != null || defaultRunfiles != null)) {
        throw new EvalException(loc, "Cannot specify the provider 'runfiles' "
            + "together with 'data_runfiles' or 'default_runfiles'");
      }
    }

    if (executable != null
        && !executable.getArtifactOwner().equals(context.getRuleContext().getOwner())) {
      throw new EvalException(
          loc,
          String.format(
              "'executable' provided by an executable rule '%s' should be created "
                  + "by the same rule.",
              context.getRuleContext().getRule().getRuleClass()));
    }

    if (executable != null && context.isExecutable() && context.isDefaultExecutableCreated()) {
        Artifact defaultExecutable = context.getRuleContext().createOutputArtifact();
        if (!executable.equals(defaultExecutable)) {
          throw new EvalException(loc,
              String.format(
                  "The rule '%s' both accesses 'ctx.outputs.executable' and provides "
                      + "a different executable '%s'. Do not use 'ctx.output.executable'.",
                  context.getRuleContext().getRule().getRuleClass(),
                  executable.getRootRelativePathString())
          );
        }
    }

    if (context.getRuleContext().getRule().isAnalysisTest()) {
      // The Starlark Build API should already throw exception if the rule implementation attempts
      // to register any actions. This is just a sanity check of this invariant.
      Preconditions.checkState(
          context.getRuleContext().getAnalysisEnvironment().getRegisteredActions().isEmpty(),
          "%s", context.getRuleContext().getLabel());

      executable = context.getRuleContext().createOutputArtifactScript();
    }

    if (executable == null && context.isExecutable()) {
      if (context.isDefaultExecutableCreated()) {
        // This doesn't actually create a new Artifact just returns the one
        // created in SkylarkRuleContext.
        executable = context.getRuleContext().createOutputArtifact();
      } else {
        throw new EvalException(loc,
            String.format("The rule '%s' is executable. "
                    + "It needs to create an executable File and pass it as the 'executable' "
                    + "parameter to the DefaultInfo it returns.",
                context.getRuleContext().getRule().getRuleClass()));
      }
    }

    addSimpleProviders(
        builder,
        context.getRuleContext(),
        loc,
        executable,
        files,
        statelessRunfiles,
        dataRunfiles,
        defaultRunfiles);
  }

  private static void addSimpleProviders(
      RuleConfiguredTargetBuilder builder,
      RuleContext ruleContext,
      Location loc,
      Artifact executable,
      @Nullable Depset files,
      Runfiles statelessRunfiles,
      Runfiles dataRunfiles,
      Runfiles defaultRunfiles)
      throws EvalException {

    // TODO(bazel-team) if both 'files' and 'executable' are provided 'files' override 'executalbe'
    NestedSetBuilder<Artifact> filesToBuild =
        NestedSetBuilder.<Artifact>stableOrder().addAll(ruleContext.getOutputArtifacts());
    if (executable != null) {
      filesToBuild.add(executable);
    }
    builder.setFilesToBuild(filesToBuild.build());

    if (files != null) {
      // If we specify files_to_build we don't have the executable in it by default.
      builder.setFilesToBuild(Depset.cast(files, Artifact.class, "files"));
    }

    if (statelessRunfiles == null && dataRunfiles == null && defaultRunfiles == null) {
      // No runfiles specified, set default
      statelessRunfiles = Runfiles.EMPTY;
    }

    RunfilesProvider runfilesProvider =
        statelessRunfiles != null
            ? RunfilesProvider.simple(mergeFiles(statelessRunfiles, executable, ruleContext))
            : RunfilesProvider.withData(
                // The executable doesn't get into the default runfiles if we have runfiles states.
                // This is to keep Starlark genrule consistent with the original genrule.
                defaultRunfiles != null ? defaultRunfiles : Runfiles.EMPTY,
                dataRunfiles != null ? dataRunfiles : Runfiles.EMPTY);
    builder.addProvider(RunfilesProvider.class, runfilesProvider);

    Runfiles computedDefaultRunfiles = runfilesProvider.getDefaultRunfiles();
    // This works because we only allowed to call a rule *_test iff it's a test type rule.
    boolean testRule = TargetUtils.isTestRuleName(ruleContext.getRule().getRuleClass());
    if (testRule && computedDefaultRunfiles.isEmpty()) {
      throw new EvalException(loc, "Test rules have to define runfiles");
    }
    if (executable != null || testRule) {
      RunfilesSupport runfilesSupport = null;
      if (!computedDefaultRunfiles.isEmpty()) {
        Preconditions.checkNotNull(executable, "executable must not be null");
        runfilesSupport =
            RunfilesSupport.withExecutable(ruleContext, computedDefaultRunfiles, executable);
        assertExecutableSymlinkPresent(runfilesSupport.getRunfiles(), executable, loc);
      }
      builder.setRunfilesSupport(runfilesSupport, executable);
    }

    if (ruleContext.getRule().getRuleClassObject().isStarlarkTestable()) {
      Info actions =
          ActionsProvider.create(ruleContext.getAnalysisEnvironment().getRegisteredActions());
      builder.addSkylarkDeclaredProvider(actions);
    }
  }

  private static void assertExecutableSymlinkPresent(
      Runfiles runfiles, Artifact executable, Location loc) throws EvalException {
    try {
      // Extracting the map from Runfiles flattens a depset.
      // TODO(cparsons): Investigate: Avoiding this flattening may be an efficiency win.
      Map<PathFragment, Artifact> symlinks = runfiles.asMapWithoutRootSymlinks();
      if (!symlinks.containsValue(executable)) {
        throw new EvalException(loc, "main program " + executable + " not included in runfiles");
      }
    } catch (NestedSetDepthException exception) {
      throw new EvalException(
          loc,
          "depset exceeded maximum depth "
              + exception.getDepthLimit()
              + ". This was only discovered when attempting to flatten the runfiles depset "
              + "returned by the rule implementation function. the size of depsets is unknown "
              + "until flattening. "
              + "See https://github.com/bazelbuild/bazel/issues/9180 for details and possible "
              + "solutions.");
    }
  }

  private static Runfiles mergeFiles(
      Runfiles runfiles, Artifact executable, RuleContext ruleContext) {
    if (executable == null) {
      return runfiles;
    }
    return new Runfiles.Builder(
        ruleContext.getWorkspaceName(), ruleContext.getConfiguration().legacyExternalRunfiles())
        .addArtifact(executable)
        .merge(runfiles).build();
  }
}