// 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 static com.google.devtools.build.lib.packages.RuleClass.Builder.SKYLARK_BUILD_SETTING_DEFAULT_ATTR_NAME;

import com.google.common.base.Function;
import com.google.common.base.Optional;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableCollection;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.collect.Ordering;
import com.google.common.hash.Hashing;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.ArtifactRoot;
import com.google.devtools.build.lib.analysis.ActionsProvider;
import com.google.devtools.build.lib.analysis.AliasProvider;
import com.google.devtools.build.lib.analysis.CommandHelper;
import com.google.devtools.build.lib.analysis.ConfigurationMakeVariableContext;
import com.google.devtools.build.lib.analysis.DefaultInfo;
import com.google.devtools.build.lib.analysis.FileProvider;
import com.google.devtools.build.lib.analysis.FilesToRunProvider;
import com.google.devtools.build.lib.analysis.LabelExpander;
import com.google.devtools.build.lib.analysis.LabelExpander.NotUniqueExpansionException;
import com.google.devtools.build.lib.analysis.LocationExpander;
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.ShToolchain;
import com.google.devtools.build.lib.analysis.TransitiveInfoCollection;
import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
import com.google.devtools.build.lib.analysis.config.FragmentCollection;
import com.google.devtools.build.lib.analysis.config.HostTransition;
import com.google.devtools.build.lib.analysis.config.transitions.NoTransition;
import com.google.devtools.build.lib.analysis.configuredtargets.RuleConfiguredTarget.Mode;
import com.google.devtools.build.lib.analysis.stringtemplate.ExpansionException;
import com.google.devtools.build.lib.analysis.test.InstrumentedFilesCollector;
import com.google.devtools.build.lib.analysis.test.InstrumentedFilesInfo;
import com.google.devtools.build.lib.cmdline.Label;
import com.google.devtools.build.lib.events.Location;
import com.google.devtools.build.lib.packages.Aspect;
import com.google.devtools.build.lib.packages.AspectDescriptor;
import com.google.devtools.build.lib.packages.Attribute;
import com.google.devtools.build.lib.packages.BuildType;
import com.google.devtools.build.lib.packages.ImplicitOutputsFunction;
import com.google.devtools.build.lib.packages.ImplicitOutputsFunction.SkylarkImplicitOutputsFunction;
import com.google.devtools.build.lib.packages.OutputFile;
import com.google.devtools.build.lib.packages.Package;
import com.google.devtools.build.lib.packages.Provider;
import com.google.devtools.build.lib.packages.RawAttributeMapper;
import com.google.devtools.build.lib.packages.StructImpl;
import com.google.devtools.build.lib.packages.StructProvider;
import com.google.devtools.build.lib.shell.ShellUtils;
import com.google.devtools.build.lib.shell.ShellUtils.TokenizationException;
import com.google.devtools.build.lib.skylarkbuildapi.FileApi;
import com.google.devtools.build.lib.skylarkbuildapi.SkylarkRuleContextApi;
import com.google.devtools.build.lib.skylarkinterface.SkylarkPrinter;
import com.google.devtools.build.lib.skylarkinterface.SkylarkValue;
import com.google.devtools.build.lib.syntax.ClassObject;
import com.google.devtools.build.lib.syntax.Environment;
import com.google.devtools.build.lib.syntax.EvalException;
import com.google.devtools.build.lib.syntax.EvalUtils;
import com.google.devtools.build.lib.syntax.FuncallExpression.FuncallException;
import com.google.devtools.build.lib.syntax.Printer;
import com.google.devtools.build.lib.syntax.Runtime;
import com.google.devtools.build.lib.syntax.SkylarkDict;
import com.google.devtools.build.lib.syntax.SkylarkIndexable;
import com.google.devtools.build.lib.syntax.SkylarkList;
import com.google.devtools.build.lib.syntax.SkylarkList.MutableList;
import com.google.devtools.build.lib.syntax.SkylarkList.Tuple;
import com.google.devtools.build.lib.syntax.SkylarkNestedSet;
import com.google.devtools.build.lib.syntax.SkylarkSemantics;
import com.google.devtools.build.lib.syntax.Type;
import com.google.devtools.build.lib.syntax.Type.ConversionException;
import com.google.devtools.build.lib.syntax.Type.LabelClass;
import com.google.devtools.build.lib.vfs.PathFragment;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import javax.annotation.Nullable;

/**
 * A Skylark API for the ruleContext.
 *
 * <p>"This object becomes featureless once the rule implementation function that it was created for
 * has completed. To achieve this, the {@link #nullify()} should be called once the evaluation of
 * the function is completed. The method both frees memory by deleting all significant fields of the
 * object and makes it impossible to accidentally use this object where it's not supposed to be used
 * (such attempts will result in {@link EvalException}s).
 */
public final class SkylarkRuleContext implements SkylarkRuleContextApi {

  public static final Function<Attribute, Object> ATTRIBUTE_VALUE_EXTRACTOR_FOR_ASPECT =
      new Function<Attribute, Object>() {
        @Nullable
        @Override
        public Object apply(Attribute attribute) {
          return attribute.getDefaultValue(null);
        }
      };
  public static final String EXECUTABLE_OUTPUT_NAME = "executable";

  // This field is a copy of the info from ruleContext, stored separately so it can be accessed
  // after this object has been nullified.
  private final String ruleLabelCanonicalName;

  private final boolean isForAspect;

  private final SkylarkActionFactory actionFactory;

  // The fields below intended to be final except that they can be cleared by calling `nullify()`
  // when the object becomes featureless.
  private RuleContext ruleContext;
  private FragmentCollection fragments;
  private FragmentCollection hostFragments;
  private AspectDescriptor aspectDescriptor;
  private final SkylarkSemantics skylarkSemantics;

  private SkylarkDict<String, String> makeVariables;
  private SkylarkAttributesCollection attributesCollection;
  private SkylarkAttributesCollection ruleAttributesCollection;
  private StructImpl splitAttributes;

  // TODO(bazel-team): we only need this because of the css_binary rule.
  private ImmutableMap<Artifact, Label> artifactsLabelMap;
  private Outputs outputsObject;

  /**
   * Creates a new SkylarkRuleContext using ruleContext.
   * @param aspectDescriptor aspect for which the context is created, or <code>null</code>
   *        if it is for a rule.
   * @throws InterruptedException
   */
  public SkylarkRuleContext(RuleContext ruleContext,
      @Nullable AspectDescriptor aspectDescriptor,
      SkylarkSemantics skylarkSemantics)
      throws EvalException, InterruptedException {
    this.actionFactory = new SkylarkActionFactory(this, skylarkSemantics, ruleContext);
    this.ruleContext = Preconditions.checkNotNull(ruleContext);
    this.ruleLabelCanonicalName = ruleContext.getLabel().getCanonicalForm();
    this.fragments = new FragmentCollection(ruleContext, NoTransition.INSTANCE);
    this.hostFragments = new FragmentCollection(ruleContext, HostTransition.INSTANCE);
    this.aspectDescriptor = aspectDescriptor;
    this.skylarkSemantics = skylarkSemantics;

    if (aspectDescriptor == null) {
      this.isForAspect = false;
      Collection<Attribute> attributes = ruleContext.getRule().getAttributes();
      Outputs outputs = new Outputs(this);

      ImplicitOutputsFunction implicitOutputsFunction =
          ruleContext.getRule().getImplicitOutputsFunction();

      if (implicitOutputsFunction instanceof SkylarkImplicitOutputsFunction) {
        SkylarkImplicitOutputsFunction func =
            (SkylarkImplicitOutputsFunction) implicitOutputsFunction;
        for (Map.Entry<String, String> entry :
            func.calculateOutputs(
                    ruleContext.getAnalysisEnvironment().getEventHandler(),
                    RawAttributeMapper.of(ruleContext.getRule()))
                .entrySet()) {
          outputs.addOutput(
              entry.getKey(),
              ruleContext.getImplicitOutputArtifact(entry.getValue()));
        }
      }

      ImmutableMap.Builder<Artifact, Label> artifactLabelMapBuilder = ImmutableMap.builder();
      for (Attribute a : attributes) {
        String attrName = a.getName();
        Type<?> type = a.getType();
        if (type.getLabelClass() != LabelClass.OUTPUT) {
          continue;
        }
        ImmutableList.Builder<Artifact> artifactsBuilder = ImmutableList.builder();
        for (OutputFile outputFile : ruleContext.getRule().getOutputFileMap().get(attrName)) {
          Artifact artifact = ruleContext.createOutputArtifact(outputFile);
          artifactsBuilder.add(artifact);
          artifactLabelMapBuilder.put(artifact, outputFile.getLabel());
        }
        ImmutableList<Artifact> artifacts = artifactsBuilder.build();

        if (type == BuildType.OUTPUT) {
          if (artifacts.size() == 1) {
            outputs.addOutput(attrName, Iterables.getOnlyElement(artifacts));
          } else {
            outputs.addOutput(attrName, Runtime.NONE);
          }
        } else if (type == BuildType.OUTPUT_LIST) {
          outputs.addOutput(attrName, SkylarkList.createImmutable(artifacts));
        } else {
          throw new IllegalArgumentException(
              "Type of " + attrName + "(" + type + ") is not output type ");
        }
      }

      this.artifactsLabelMap = artifactLabelMapBuilder.build();
      this.outputsObject = outputs;

      SkylarkAttributesCollection.Builder builder = SkylarkAttributesCollection.builder(this);
      for (Attribute attribute : ruleContext.getRule().getAttributes()) {
        Object value = ruleContext.attributes().get(attribute.getName(), attribute.getType());
        builder.addAttribute(attribute, value);
      }

      this.attributesCollection = builder.build();
      this.splitAttributes = buildSplitAttributeInfo(attributes, ruleContext);
      this.ruleAttributesCollection = null;
    } else { // ASPECT
      this.isForAspect = true;
      this.artifactsLabelMap = ImmutableMap.of();
      this.outputsObject = null;

      ImmutableCollection<Attribute> attributes =
          ruleContext.getMainAspect().getDefinition().getAttributes().values();
      SkylarkAttributesCollection.Builder aspectBuilder = SkylarkAttributesCollection.builder(this);
      for (Attribute attribute : attributes) {
        aspectBuilder.addAttribute(attribute, attribute.getDefaultValue(null));
      }
      this.attributesCollection = aspectBuilder.build();

      this.splitAttributes = null;
      SkylarkAttributesCollection.Builder ruleBuilder = SkylarkAttributesCollection.builder(this);

      for (Attribute attribute : ruleContext.getRule().getAttributes()) {
        Object value = ruleContext.attributes().get(attribute.getName(), attribute.getType());
        ruleBuilder.addAttribute(attribute, value);
      }
      for (Aspect aspect : ruleContext.getAspects()) {
        if (aspect.equals(ruleContext.getMainAspect())) {
          // Aspect's own attributes are in <code>attributesCollection</code>.
          continue;
        }
        for (Attribute attribute : aspect.getDefinition().getAttributes().values()) {
          ruleBuilder.addAttribute(attribute, attribute.getDefaultValue(null));
        }
      }

      this.ruleAttributesCollection = ruleBuilder.build();
    }

    makeVariables = ruleContext.getConfigurationMakeVariableContext().collectMakeVariables();
  }

  /**
   * Represents `ctx.outputs`.
   *
   * <p>A {@link ClassObject} (struct-like data structure) with "executable" field created
   * lazily on-demand.
   *
   * <p>Note: There is only one {@code Outputs} object per rule context, so default
   * (object identity) equals and hashCode suffice.
   */
  private static class Outputs implements ClassObject, SkylarkValue {
    private final Map<String, Object> outputs;
    private final SkylarkRuleContext context;
    private boolean executableCreated = false;

    public Outputs(SkylarkRuleContext context) {
      this.outputs = new LinkedHashMap<>();
      this.context = context;
    }

    private void addOutput(String key, Object value)
        throws EvalException {
      Preconditions.checkState(!context.isImmutable(),
          "Cannot add outputs to immutable Outputs object");
      if (outputs.containsKey(key)
          || (context.isExecutable() && EXECUTABLE_OUTPUT_NAME.equals(key))) {
        throw new EvalException(null, "Multiple outputs with the same key: " + key);
      }
      outputs.put(key, value);
    }


    @Override
    public boolean isImmutable() {
      return context.isImmutable();
    }

    @Override
    public ImmutableCollection<String> getFieldNames() throws EvalException {
      checkMutable();
      ImmutableList.Builder<String> result = ImmutableList.builder();
      if (context.isExecutable() && executableCreated) {
        result.add(EXECUTABLE_OUTPUT_NAME);
      }
      result.addAll(outputs.keySet());
      return result.build();
    }

    @Nullable
    @Override
    public Object getValue(String name) throws EvalException {
      checkMutable();
      if (context.isExecutable() && EXECUTABLE_OUTPUT_NAME.equals(name)) {
        executableCreated = true;
        // createOutputArtifact() will cache the created artifact.
        return context.getRuleContext().createOutputArtifact();
      }

      return outputs.get(name);
    }

    @Nullable
    @Override
    public String getErrorMessageForUnknownField(String name) {
      return String.format(
          "No attribute '%s' in outputs. Make sure you declared a rule output with this name.",
          name);
    }

    @Override
    public void repr(SkylarkPrinter printer) {
      if (isImmutable()) {
        printer.append("ctx.outputs(for ");
        printer.append(context.ruleLabelCanonicalName);
        printer.append(")");
        return;
      }
      boolean first = true;
      printer.append("ctx.outputs(");
      // Sort by field name to ensure deterministic output.
      try {
        for (String field : Ordering.natural().sortedCopy(getFieldNames())) {
          if (!first) {
            printer.append(", ");
          }
          first = false;
          printer.append(field);
          printer.append(" = ");
          printer.repr(getValue(field));
        }
        printer.append(")");
      } catch (EvalException e) {
        throw new AssertionError("mutable ctx.outputs should not throw", e);
      }
    }

    private void checkMutable() throws EvalException {
      if (isImmutable()) {
        throw new EvalException(
            null,
            String.format(
                "cannot access outputs of rule '%s' outside of its own "
                    + "rule implementation function",
                context.ruleLabelCanonicalName));
      }
    }

  }

  public boolean isExecutable() {
    return ruleContext.getRule().getRuleClassObject().isExecutableSkylark();
  }

  public boolean isDefaultExecutableCreated() {
    return this.outputsObject.executableCreated;
  }


  /**
   * Nullifies fields of the object when it's not supposed to be used anymore to free unused memory
   * and to make sure this object is not accessed when it's not supposed to (after the corresponding
   * rule implementation function has exited).
   */
  public void nullify() {
    actionFactory.nullify();
    ruleContext = null;
    fragments = null;
    hostFragments = null;
    aspectDescriptor = null;
    makeVariables = null;
    attributesCollection = null;
    ruleAttributesCollection = null;
    splitAttributes = null;
    artifactsLabelMap = null;
    outputsObject = null;
  }

  public void checkMutable(String attrName) throws EvalException {
    if (isImmutable()) {
      throw new EvalException(null, String.format(
          "cannot access field or method '%s' of rule context for '%s' outside of its own rule " 
              + "implementation function", attrName, ruleLabelCanonicalName));
    }
  }

  @Nullable
  public AspectDescriptor getAspectDescriptor() {
    return aspectDescriptor;
  }

  public String getRuleLabelCanonicalName() {
    return ruleLabelCanonicalName;
  }

  private static StructImpl buildSplitAttributeInfo(
      Collection<Attribute> attributes, RuleContext ruleContext) {

    ImmutableMap.Builder<String, Object> splitAttrInfos = ImmutableMap.builder();
    for (Attribute attr : attributes) {

      if (attr.hasSplitConfigurationTransition()) {

        Map<Optional<String>, ? extends List<? extends TransitiveInfoCollection>> splitPrereqs =
            ruleContext.getSplitPrerequisites(attr.getName());

        Map<Object, Object> splitPrereqsMap = new LinkedHashMap<>();
        for (Map.Entry<Optional<String>, ? extends List<? extends TransitiveInfoCollection>>
            splitPrereq : splitPrereqs.entrySet()) {

          Object value;
          if (attr.getType() == BuildType.LABEL) {
            Preconditions.checkState(splitPrereq.getValue().size() == 1);
            value = splitPrereq.getValue().get(0);
          } else {
            // BuildType.LABEL_LIST
            value = SkylarkList.createImmutable(splitPrereq.getValue());
          }

          if (splitPrereq.getKey().isPresent()) {
            splitPrereqsMap.put(splitPrereq.getKey().get(), value);
          } else {
            // If the split transition is not in effect, then the key will be missing since there's
            // nothing to key on because the dependencies aren't split and getSplitPrerequisites()
            // behaves like getPrerequisites(). This also means there should be only one entry in
            // the map. Use None in Skylark to represent this.
            Preconditions.checkState(splitPrereqs.size() == 1);
            splitPrereqsMap.put(Runtime.NONE, value);
          }
        }

        splitAttrInfos.put(attr.getPublicName(), SkylarkDict.copyOf(null, splitPrereqsMap));
      }
    }

    return StructProvider.STRUCT.create(
        splitAttrInfos.build(),
        "No attribute '%s' in split_attr. Make sure that this attribute is defined with a "
            + "split configuration.");
  }

  @Override
  public boolean isImmutable() {
    return ruleContext == null;
  }

  @Override
  public void repr(SkylarkPrinter printer) {
    if (isForAspect) {
      printer.append("<aspect context for " + ruleLabelCanonicalName + ">");
    } else {
      printer.append("<rule context for " + ruleLabelCanonicalName + ">");
    }
  }

  /**
   * Returns the original ruleContext.
   */
  public RuleContext getRuleContext() {
    return ruleContext;
  }

  @Override
  public Provider getDefaultProvider() {
    return DefaultInfo.PROVIDER;
  }

  @Override
  public SkylarkActionFactory actions() {
    return actionFactory;
  }

  @Override
  public SkylarkValue createdActions() throws EvalException {
    checkMutable("created_actions");
    if (ruleContext.getRule().getRuleClassObject().isSkylarkTestable()) {
      return ActionsProvider.create(
          ruleContext.getAnalysisEnvironment().getRegisteredActions());
    } else {
      return Runtime.NONE;
    }
  }

  @Override
  public StructImpl getAttr() throws EvalException {
    checkMutable("attr");
    return attributesCollection.getAttr();
  }

  @Override
  public StructImpl getSplitAttr() throws EvalException {
    checkMutable("split_attr");
    if (splitAttributes == null) {
      throw new EvalException(
          Location.BUILTIN, "'split_attr' is available only in rule implementations");
    }
    return splitAttributes;
  }

  /** See {@link RuleContext#getExecutablePrerequisite(String, Mode)}. */
  @Override
  public StructImpl getExecutable() throws EvalException {
    checkMutable("executable");
    return attributesCollection.getExecutable();
  }

  /** See {@link RuleContext#getPrerequisiteArtifact(String, Mode)}. */
  @Override
  public StructImpl getFile() throws EvalException {
    checkMutable("file");
    return attributesCollection.getFile();
  }

  /** See {@link RuleContext#getPrerequisiteArtifacts(String, Mode)}. */
  @Override
  public StructImpl getFiles() throws EvalException {
    checkMutable("files");
    return attributesCollection.getFiles();
  }

  @Override
  public String getWorkspaceName() throws EvalException {
    checkMutable("workspace_name");
    return ruleContext.getWorkspaceName();
  }

  @Override
  public Label getLabel() throws EvalException {
    checkMutable("label");
    return ruleContext.getLabel();
  }

  @Override
  public FragmentCollection getFragments() throws EvalException {
    checkMutable("fragments");
    return fragments;
  }

  @Override
  public FragmentCollection getHostFragments() throws EvalException {
    checkMutable("host_fragments");
    return hostFragments;
  }

  @Override
  public BuildConfiguration getConfiguration() throws EvalException {
    checkMutable("configuration");
    return ruleContext.getConfiguration();
  }

  @Override
  public BuildConfiguration getHostConfiguration() throws EvalException {
    checkMutable("host_configuration");
    return ruleContext.getHostConfiguration();
  }

  // TODO(juliexxia): special-case label-typed build settings so they return the providers of the
  // target represented by the label instead of the actual label.
  @Override
  @Nullable
  public Object getBuildSettingValue() throws EvalException {
    if (ruleContext.getRule().getRuleClassObject().getBuildSetting() == null) {
      throw new EvalException(
          Location.BUILTIN,
          String.format(
              "attempting to access 'build_setting_value' of non-build setting %s",
              ruleLabelCanonicalName));
    }
    ImmutableMap<Label, Object> skylarkFlagSettings =
        ruleContext.getConfiguration().getOptions().getStarlarkOptions();

    Type<?> buildSettingType =
        ruleContext.getRule().getRuleClassObject().getBuildSetting().getType();
    if (skylarkFlagSettings.containsKey(ruleContext.getLabel())) {
      return skylarkFlagSettings.get(ruleContext.getLabel());
    } else {
      return ruleContext
          .attributes()
          .get(SKYLARK_BUILD_SETTING_DEFAULT_ATTR_NAME, buildSettingType);
    }
  }

  @Override
  public boolean instrumentCoverage(Object targetUnchecked) throws EvalException {
    checkMutable("coverage_instrumented");
    BuildConfiguration config = ruleContext.getConfiguration();
    if (!config.isCodeCoverageEnabled()) {
      return false;
    }
    if (targetUnchecked == Runtime.NONE) {
      return InstrumentedFilesCollector.shouldIncludeLocalSources(
          ruleContext.getConfiguration(), ruleContext.getLabel(), ruleContext.isTestTarget());
    }
    TransitiveInfoCollection target = (TransitiveInfoCollection) targetUnchecked;
    return (target.get(InstrumentedFilesInfo.SKYLARK_CONSTRUCTOR) != null)
        && InstrumentedFilesCollector.shouldIncludeLocalSources(config, target);
  }

  @Override
  public ImmutableList<String> getFeatures() throws EvalException {
    checkMutable("features");
    return ImmutableList.copyOf(ruleContext.getFeatures());
  }

  @Override
  public ImmutableList<String> getDisabledFeatures() throws EvalException {
    checkMutable("disabled_features");
    return ImmutableList.copyOf(ruleContext.getDisabledFeatures());
  }

  @Override
  public ArtifactRoot getBinDirectory() throws EvalException {
    checkMutable("bin_dir");
    return getConfiguration().getBinDirectory(ruleContext.getRule().getRepository());
  }

  @Override
  public ArtifactRoot getGenfilesDirectory() throws EvalException {
    checkMutable("genfiles_dir");
    return getConfiguration().getGenfilesDirectory(ruleContext.getRule().getRepository());
  }

  @Override
  public ClassObject outputs() throws EvalException {
    checkMutable("outputs");
    if (outputsObject == null) {
      throw new EvalException(Location.BUILTIN, "'outputs' is not defined");
    }
    return outputsObject;
  }

  @Override
  public SkylarkAttributesCollection rule() throws EvalException {
    checkMutable("rule");
    if (!isForAspect) {
      throw new EvalException(
          Location.BUILTIN, "'rule' is only available in aspect implementations");
    }
    return ruleAttributesCollection;
  }

  @Override
  public ImmutableList<String> aspectIds() throws EvalException {
    checkMutable("aspect_ids");
    if (!isForAspect) {
      throw new EvalException(
          Location.BUILTIN, "'aspect_ids' is only available in aspect implementations");
    }

    ImmutableList.Builder<String> result = ImmutableList.builder();
    for (AspectDescriptor descriptor : ruleContext.getAspectDescriptors()) {
      result.add(descriptor.getDescription());
    }
    return result.build();
  }

  @Override
  public SkylarkDict<String, String> var() throws EvalException {
    checkMutable("var");
    return makeVariables;
  }

  @Override
  public SkylarkIndexable toolchains() throws EvalException {
    checkMutable("toolchains");
    return ruleContext.getToolchainContext();
  }

  @Override
  public String toString() {
    return ruleLabelCanonicalName;
  }

  @Override
  public SkylarkList<String> tokenize(String optionString) throws FuncallException, EvalException {
    checkMutable("tokenize");
    List<String> options = new ArrayList<>();
    try {
      ShellUtils.tokenize(options, optionString);
    } catch (TokenizationException e) {
      throw new FuncallException(e.getMessage() + " while tokenizing '" + optionString + "'");
    }
    return SkylarkList.createImmutable(options);
  }

  @Override
  public String expand(
      @Nullable String expression, SkylarkList<Object> artifacts, Label labelResolver)
      throws EvalException, FuncallException {
    checkMutable("expand");
    try {
      Map<Label, Iterable<Artifact>> labelMap = new HashMap<>();
      for (Artifact artifact : artifacts.getContents(Artifact.class, "artifacts")) {
        labelMap.put(artifactsLabelMap.get(artifact), ImmutableList.of(artifact));
      }
      return LabelExpander.expand(expression, labelMap, labelResolver);
    } catch (NotUniqueExpansionException e) {
      throw new FuncallException(e.getMessage() + " while expanding '" + expression + "'");
    }
  }

  boolean isForAspect() {
    return isForAspect;
  }

  @Override
  public Artifact newFile(Object var1,
      Object var2,
      Object fileSuffix,
      Location loc) throws EvalException {
    checkDeprecated("ctx.actions.declare_file", "ctx.new_file", null, skylarkSemantics);
    checkMutable("new_file");

    // Determine which of new_file's four signatures is being used. Yes, this is terrible.
    // It's one major reason that this method is deprecated.
    if (fileSuffix != Runtime.UNBOUND) {
      // new_file(file_root, sibling_file, suffix)
      ArtifactRoot root =
          assertTypeForNewFile(var1, ArtifactRoot.class, loc,
              "expected first param to be of type 'root'");
      Artifact siblingFile =
          assertTypeForNewFile(var2, Artifact.class, loc,
              "expected second param to be of type 'File'");
      PathFragment original = siblingFile.getRootRelativePath();
      PathFragment fragment = original.replaceName(original.getBaseName() + fileSuffix);
      return ruleContext.getDerivedArtifact(fragment, root);

    } else if (var2 == Runtime.UNBOUND) {
      // new_file(filename)
      String filename =
          assertTypeForNewFile(var1, String.class, loc,
              "expected first param to be of type 'string'");
      return actionFactory.declareFile(filename, Runtime.NONE);

    } else {
      String filename = assertTypeForNewFile(var2, String.class, loc,
          "expected second param to be of type 'string'");
      if (var1 instanceof ArtifactRoot) {
        // new_file(root, filename)
        ArtifactRoot root = (ArtifactRoot) var1;

        return ruleContext.getPackageRelativeArtifact(filename, root);
      } else {
        // new_file(sibling_file, filename)
        Artifact siblingFile =
            assertTypeForNewFile(var1, Artifact.class, loc,
                "expected first param to be of type 'File' or 'root'");

        return actionFactory.declareFile(filename, siblingFile);
      }
    }
  }

  private static <T> T assertTypeForNewFile(Object obj, Class<T> type, Location loc,
      String errorMessage) throws EvalException {
    if (type.isInstance(obj)) {
      return (T) obj;
    } else {
      throw new EvalException(loc, errorMessage);
    }
  }

  @Override
  public Artifact newDirectory(String name, Object siblingArtifactUnchecked) throws EvalException {
    checkDeprecated(
        "ctx.actions.declare_directory", "ctx.experimental_new_directory", null, skylarkSemantics);
    checkMutable("experimental_new_directory");
    return actionFactory.declareDirectory(name, siblingArtifactUnchecked);
  }

  @Override
  public boolean checkPlaceholders(String template, SkylarkList<Object> allowedPlaceholders)
      throws EvalException {
    checkMutable("check_placeholders");
    List<String> actualPlaceHolders = new LinkedList<>();
    Set<String> allowedPlaceholderSet =
        ImmutableSet.copyOf(allowedPlaceholders.getContents(String.class, "allowed_placeholders"));
    ImplicitOutputsFunction.createPlaceholderSubstitutionFormatString(template, actualPlaceHolders);
    for (String placeholder : actualPlaceHolders) {
      if (!allowedPlaceholderSet.contains(placeholder)) {
        return false;
      }
    }
    return true;
  }

  @Override
  public String expandMakeVariables(
      String attributeName, String command, final Map<String, String> additionalSubstitutions)
      throws EvalException {
    checkMutable("expand_make_variables");
    ConfigurationMakeVariableContext makeVariableContext =
        new ConfigurationMakeVariableContext(
            this.getRuleContext(),
            ruleContext.getRule().getPackage(),
            ruleContext.getConfiguration(),
            ImmutableList.of()) {
          @Override
          public String lookupVariable(String variableName) throws ExpansionException {
            if (additionalSubstitutions.containsKey(variableName)) {
              return additionalSubstitutions.get(variableName);
            } else {
              return super.lookupVariable(variableName);
            }
          }
        };
    return ruleContext.getExpander(makeVariableContext).expand(attributeName, command);
  }


  FilesToRunProvider getExecutableRunfiles(Artifact executable) {
    return attributesCollection.getExecutableRunfilesMap().get(executable);
  }

  @Override
  public Artifact getStableWorkspaceStatus() throws InterruptedException, EvalException {
    checkMutable("info_file");
    return ruleContext.getAnalysisEnvironment().getStableWorkspaceStatusArtifact();
  }

  @Override
  public Artifact getVolatileWorkspaceStatus() throws InterruptedException, EvalException {
    checkMutable("version_file");
    return ruleContext.getAnalysisEnvironment().getVolatileWorkspaceStatusArtifact();
  }

  @Override
  public String getBuildFileRelativePath() throws EvalException {
    checkMutable("build_file_path");
    Package pkg = ruleContext.getRule().getPackage();
    return pkg.getSourceRoot().relativize(pkg.getBuildFile().getPath()).getPathString();
  }

  /**
   * A Skylark built-in function to create and register a SpawnAction using a dictionary of
   * parameters: action( inputs = [input1, input2, ...], outputs = [output1, output2, ...],
   * executable = executable, arguments = [argument1, argument2, ...], mnemonic = 'Mnemonic',
   * command = 'command', )
   */
  @Override
  public Runtime.NoneType action(
      SkylarkList outputs,
      Object inputs,
      Object executableUnchecked,
      Object toolsUnchecked,
      Object arguments,
      Object mnemonicUnchecked,
      Object commandUnchecked,
      Object progressMessage,
      Boolean useDefaultShellEnv,
      Object envUnchecked,
      Object executionRequirementsUnchecked,
      Object inputManifestsUnchecked,
      Location loc,
      Environment env)
      throws EvalException {
    checkDeprecated(
        "ctx.actions.run or ctx.actions.run_shell", "ctx.action", loc, env.getSemantics());
    checkMutable("action");
    if ((commandUnchecked == Runtime.NONE) == (executableUnchecked == Runtime.NONE)) {
      throw new EvalException(loc, "You must specify either 'command' or 'executable' argument");
    }
    boolean hasCommand = commandUnchecked != Runtime.NONE;
    if (!hasCommand) {
      actions()
          .run(
              outputs,
              inputs,
              executableUnchecked,
              toolsUnchecked,
              arguments,
              mnemonicUnchecked,
              progressMessage,
              useDefaultShellEnv,
              envUnchecked,
              executionRequirementsUnchecked,
              inputManifestsUnchecked,
              loc);

    } else {
      actions()
          .runShell(
              outputs,
              inputs,
              toolsUnchecked,
              arguments,
              mnemonicUnchecked,
              commandUnchecked,
              progressMessage,
              useDefaultShellEnv,
              envUnchecked,
              executionRequirementsUnchecked,
              inputManifestsUnchecked,
              loc);
    }
    return Runtime.NONE;
  }

  @Override
  public String expandLocation(String input, SkylarkList targets, Location loc, Environment env)
      throws EvalException {
    checkMutable("expand_location");
    try {
      return LocationExpander.withExecPaths(
              getRuleContext(),
              makeLabelMap(targets.getContents(TransitiveInfoCollection.class, "targets")))
          .expand(input);
    } catch (IllegalStateException ise) {
      throw new EvalException(loc, ise);
    }
  }

  @Override
  public Runtime.NoneType fileAction(
      FileApi output, String content, Boolean executable, Location loc, Environment env)
      throws EvalException {
    checkDeprecated("ctx.actions.write", "ctx.file_action", loc, env.getSemantics());
    checkMutable("file_action");
    actions().write(output, content, executable, loc);
    return Runtime.NONE;
  }

  @Override
  public Runtime.NoneType emptyAction(String mnemonic, Object inputs, Location loc, Environment env)
      throws EvalException {
    checkDeprecated("ctx.actions.do_nothing", "ctx.empty_action", loc, env.getSemantics());
    checkMutable("empty_action");
    actions().doNothing(mnemonic, inputs, loc);
    return Runtime.NONE;
  }

  @Override
  public Runtime.NoneType templateAction(
      FileApi template,
      FileApi output,
      SkylarkDict<?, ?> substitutionsUnchecked,
      Boolean executable,
      Location loc,
      Environment env)
      throws EvalException {
    checkDeprecated("ctx.actions.expand_template", "ctx.template_action", loc, env.getSemantics());
    checkMutable("template_action");
    actions().expandTemplate(template, output, substitutionsUnchecked, executable, loc);
    return Runtime.NONE;
  }

  @Override
  public Runfiles runfiles(
      SkylarkList files,
      Object transitiveFiles,
      Boolean collectData,
      Boolean collectDefault,
      SkylarkDict<?, ?> symlinks,
      SkylarkDict<?, ?> rootSymlinks,
      Location loc)
      throws EvalException, ConversionException {
    checkMutable("runfiles");
    Runfiles.Builder builder =
        new Runfiles.Builder(
            getRuleContext().getWorkspaceName(), getConfiguration().legacyExternalRunfiles());
    boolean checkConflicts = false;
    if (EvalUtils.toBoolean(collectData)) {
      builder.addRunfiles(getRuleContext(), RunfilesProvider.DATA_RUNFILES);
    }
    if (EvalUtils.toBoolean(collectDefault)) {
      builder.addRunfiles(getRuleContext(), RunfilesProvider.DEFAULT_RUNFILES);
    }
    if (!files.isEmpty()) {
      builder.addArtifacts(files.getContents(Artifact.class, "files"));
    }
    if (transitiveFiles != Runtime.NONE) {
      builder.addTransitiveArtifacts(((SkylarkNestedSet) transitiveFiles).getSet(Artifact.class));
    }
    if (!symlinks.isEmpty()) {
      // If Skylark code directly manipulates symlinks, activate more stringent validity checking.
      checkConflicts = true;
      for (Map.Entry<String, Artifact> entry :
          symlinks.getContents(String.class, Artifact.class, "symlinks").entrySet()) {
        builder.addSymlink(PathFragment.create(entry.getKey()), entry.getValue());
      }
    }
    if (!rootSymlinks.isEmpty()) {
      checkConflicts = true;
      for (Map.Entry<String, Artifact> entry :
          rootSymlinks.getContents(String.class, Artifact.class, "root_symlinks").entrySet()) {
        builder.addRootSymlink(PathFragment.create(entry.getKey()), entry.getValue());
      }
    }
    Runfiles runfiles = builder.build();
    if (checkConflicts) {
      runfiles.setConflictPolicy(Runfiles.ConflictPolicy.ERROR);
    }
    return runfiles;
  }

  @Override
  public Tuple<Object> resolveCommand(
      String command,
      Object attributeUnchecked,
      Boolean expandLocations,
      Object makeVariablesUnchecked,
      SkylarkList tools,
      SkylarkDict<?, ?> labelDictUnchecked,
      SkylarkDict<?, ?> executionRequirementsUnchecked,
      Location loc,
      Environment env)
      throws ConversionException, EvalException {
    checkMutable("resolve_command");
    Label ruleLabel = getLabel();
    Map<Label, Iterable<Artifact>> labelDict = checkLabelDict(labelDictUnchecked, loc, env);
    // The best way to fix this probably is to convert CommandHelper to Skylark.
    CommandHelper helper =
        CommandHelper.builder(getRuleContext())
            .addToolDependencies(tools.getContents(TransitiveInfoCollection.class, "tools"))
            .addLabelMap(labelDict)
            .build();
    String attribute = Type.STRING.convertOptional(attributeUnchecked, "attribute", ruleLabel);
    if (expandLocations) {
      command =
          helper.resolveCommandAndExpandLabels(command, attribute, /*allowDataInLabel=*/ false);
    }
    if (!EvalUtils.isNullOrNone(makeVariablesUnchecked)) {
      Map<String, String> makeVariables =
          Type.STRING_DICT.convert(makeVariablesUnchecked, "make_variables", ruleLabel);
      command = expandMakeVariables(attribute, command, makeVariables);
    }
    List<Artifact> inputs = new ArrayList<>();
    // TODO(lberki): This flattens a NestedSet.
    // However, we can't turn this into a SkylarkNestedSet because it's an incompatible change to
    // Skylark.
    Iterables.addAll(inputs, helper.getResolvedTools());

    ImmutableMap<String, String> executionRequirements =
        ImmutableMap.copyOf(
            SkylarkDict.castSkylarkDictOrNoneToDict(
                executionRequirementsUnchecked,
                String.class,
                String.class,
                "execution_requirements"));
    PathFragment shExecutable = ShToolchain.getPathOrError(ruleContext);
    List<String> argv =
        helper.buildCommandLine(
            shExecutable,
            command,
            inputs,
            // Hash the command-line to prevent multiple actions from the same rule invocation
            // conflicting with each other.
            "." + Hashing.murmur3_32().hashUnencodedChars(command).toString() + SCRIPT_SUFFIX,
            executionRequirements);
    return Tuple.<Object>of(
        MutableList.copyOf(env, inputs),
        MutableList.copyOf(env, argv),
        helper.getToolsRunfilesSuppliers());
  }

  @Override
  public Tuple<Object> resolveTools(SkylarkList tools) throws ConversionException, EvalException {
    checkMutable("resolve_tools");
    CommandHelper helper =
        CommandHelper.builder(getRuleContext())
            .addToolDependencies(tools.getContents(TransitiveInfoCollection.class, "tools"))
            .build();
    return Tuple.<Object>of(
        SkylarkNestedSet.of(Artifact.class, helper.getResolvedTools()),
        helper.getToolsRunfilesSuppliers());
  }

  public SkylarkSemantics getSkylarkSemantics() {
    return skylarkSemantics;
  }

  /**
   * Ensures the given {@link Map} has keys that have {@link Label} type and values that have either
   * {@link Iterable} or {@link SkylarkNestedSet} type, and raises {@link EvalException} otherwise.
   * Returns a corresponding map where any sets are replaced by iterables.
   */
  // TODO(bazel-team): find a better way to typecheck this argument.
  @SuppressWarnings("unchecked")
  private static Map<Label, Iterable<Artifact>> checkLabelDict(
      Map<?, ?> labelDict, Location loc, Environment env) throws EvalException {
    Map<Label, Iterable<Artifact>> convertedMap = new HashMap<>();
    for (Map.Entry<?, ?> entry : labelDict.entrySet()) {
      Object key = entry.getKey();
      if (!(key instanceof Label)) {
        throw new EvalException(loc, Printer.format("invalid key %r in 'label_dict'", key));
      }
      ImmutableList.Builder<Artifact> files = ImmutableList.builder();
      Object val = entry.getValue();
      Iterable<?> valIter;
      try {
        valIter = EvalUtils.toIterableStrict(val, loc, env);
      } catch (EvalException ex) {
        // EvalException is thrown only if the type is wrong.
        throw new EvalException(
            loc, Printer.format("invalid value %r in 'label_dict': " + ex, val));
      }
      for (Object file : valIter) {
        if (!(file instanceof Artifact)) {
          throw new EvalException(loc, Printer.format("invalid value %r in 'label_dict'", val));
        }
        files.add((Artifact) file);
      }
      convertedMap.put((Label) key, files.build());
    }
    return convertedMap;
  }

  /** suffix of script to be used in case the command is too long to fit on a single line */
  private static final String SCRIPT_SUFFIX = ".script.sh";

  private static void checkDeprecated(
      String newApi, String oldApi, Location loc, SkylarkSemantics semantics) throws EvalException {
    if (semantics.incompatibleNewActionsApi()) {
      throw new EvalException(
          loc,
          "Use "
              + newApi
              + " instead of "
              + oldApi
              + ". \n"
              + "Use --incompatible_new_actions_api=false to temporarily disable this check.");
    }
  }

  /**
   * Builds a map: Label -> List of files from the given labels
   *
   * @param knownLabels List of known labels
   * @return Immutable map with immutable collections as values
   */
  private static ImmutableMap<Label, ImmutableCollection<Artifact>> makeLabelMap(
      Iterable<TransitiveInfoCollection> knownLabels) {
    ImmutableMap.Builder<Label, ImmutableCollection<Artifact>> builder = ImmutableMap.builder();

    for (TransitiveInfoCollection current : knownLabels) {
      builder.put(
          AliasProvider.getDependencyLabel(current),
          ImmutableList.copyOf(current.getProvider(FileProvider.class).getFilesToBuild()));
    }

    return builder.build();
  }
}