path: root/src/main/java/com/google/devtools/build/lib/rules/SkylarkRuleImplementationFunctions.java

// 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.rules;

import com.google.common.collect.ImmutableCollection;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.devtools.build.lib.actions.Action;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.extra.SpawnInfo;
import com.google.devtools.build.lib.analysis.AbstractConfiguredTarget;
import com.google.devtools.build.lib.analysis.CommandHelper;
import com.google.devtools.build.lib.analysis.FileProvider;
import com.google.devtools.build.lib.analysis.FilesToRunProvider;
import com.google.devtools.build.lib.analysis.LocationExpander;
import com.google.devtools.build.lib.analysis.PseudoAction;
import com.google.devtools.build.lib.analysis.RuleConfiguredTarget.Mode;
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.TransitiveInfoCollection;
import com.google.devtools.build.lib.analysis.TransitiveInfoProvider;
import com.google.devtools.build.lib.analysis.actions.FileWriteAction;
import com.google.devtools.build.lib.analysis.actions.SpawnAction;
import com.google.devtools.build.lib.analysis.actions.TemplateExpansionAction;
import com.google.devtools.build.lib.analysis.actions.TemplateExpansionAction.Substitution;
import com.google.devtools.build.lib.cmdline.Label;
import com.google.devtools.build.lib.collect.nestedset.NestedSet;
import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
import com.google.devtools.build.lib.events.Location;
import com.google.devtools.build.lib.packages.Attribute;
import com.google.devtools.build.lib.packages.Attribute.ConfigurationTransition;
import com.google.devtools.build.lib.packages.AttributeMap;
import com.google.devtools.build.lib.skylarkinterface.SkylarkSignature;
import com.google.devtools.build.lib.skylarkinterface.SkylarkSignature.Param;
import com.google.devtools.build.lib.syntax.BuiltinFunction;
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.Printer;
import com.google.devtools.build.lib.syntax.Runtime;
import com.google.devtools.build.lib.syntax.SkylarkDict;
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.SkylarkSignatureProcessor;
import com.google.devtools.build.lib.syntax.Type;
import com.google.devtools.build.lib.syntax.Type.ConversionException;
import com.google.devtools.build.lib.vfs.PathFragment;

import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ExecutionException;

// TODO(bazel-team): function argument names are often duplicated,
// figure out a nicely readable way to get rid of the duplications.
/**
 * A helper class to provide an easier API for Skylark rule implementations
 * and hide the original Java API. This is experimental code.
 */
public class SkylarkRuleImplementationFunctions {

  // TODO(bazel-team): add all the remaining parameters
  // TODO(bazel-team): merge executable and arguments
  /**
   * A Skylark built-in function to create and register a SpawnAction using a
   * dictionary of parameters:
   * createSpawnAction(
   *         inputs = [input1, input2, ...],
   *         outputs = [output1, output2, ...],
   *         executable = executable,
   *         arguments = [argument1, argument2, ...],
   *         mnemonic = 'Mnemonic',
   *         command = 'command',
   *     )
   */
  @SkylarkSignature(
    name = "action",
    doc =
        "Creates an action that runs an executable or a shell command. You must specify either "
            + "<code>command</code> or <code>executable</code>.\n"
            + "Actions and genrules are very similar, but have different use cases. Actions are "
            + "used inside rules, and genrules are used inside macros. Genrules also have make "
            + "variable expansion.",
    objectType = SkylarkRuleContext.class,
    returnType = Runtime.NoneType.class,
    mandatoryPositionals = {
      @Param(name = "self", type = SkylarkRuleContext.class, doc = "This RuleContext.")
    },
    mandatoryNamedOnly = {
      @Param(
        name = "outputs",
        type = SkylarkList.class,
        generic1 = Artifact.class,
        doc = "list of the output files of the action"
      )
    },
    optionalNamedOnly = {
      @Param(
        name = "inputs",
        type = SkylarkList.class,
        generic1 = Artifact.class,
        defaultValue = "[]",
        doc = "list of the input files of the action"
      ),
      @Param(
        name = "executable",
        type = Object.class, // File or PathFragment or None
        defaultValue = "None",
        doc = "the executable file to be called by the action"
      ),
      @Param(
        name = "arguments",
        type = SkylarkList.class,
        generic1 = String.class,
        defaultValue = "[]",
        doc = "command line arguments of the action"
      ),
      @Param(
        name = "mnemonic",
        type = String.class,
        noneable = true,
        defaultValue = "None",
        doc = "a one-word description of the action, e.g. CppCompile or GoLink"
      ),
      @Param(
        name = "command",
        type = Object.class, // string or ListOf(string) or NoneType
        defaultValue = "None",
        doc =
            "shell command to execute. It is usually preferable to "
                + "use <code>executable</code> instead. "
                + "Arguments are available with <code>$1</code>, <code>$2</code>, etc."
      ),
      @Param(
        name = "progress_message",
        type = String.class,
        noneable = true,
        defaultValue = "None",
        doc =
            "progress message to show to the user during the build, "
                + "e.g. \"Compiling foo.cc to create foo.o\""
      ),
      @Param(
        name = "use_default_shell_env",
        type = Boolean.class,
        defaultValue = "False",
        doc = "whether the action should use the built in shell environment or not"
      ),
      @Param(
        name = "env",
        type = SkylarkDict.class,
        noneable = true,
        defaultValue = "None",
        doc = "sets the dictionary of environment variables"
      ),
      @Param(
        name = "execution_requirements",
        type = SkylarkDict.class,
        noneable = true,
        defaultValue = "None",
        doc =
            "information for scheduling the action."
                + " See [tags](/docs/be/common-definitions.html#common.tags) for useful keys."
      ),
      @Param(
        name = "input_manifests",
        type = SkylarkDict.class,
        noneable = true,
        defaultValue = "None",
        doc =
            "sets the map of input manifests files; "
                + "they are typically generated by resolve_command"
      )
    },
    useLocation = true
  )
  private static final BuiltinFunction createSpawnAction =
      new BuiltinFunction("action") {
        public Runtime.NoneType invoke(
            SkylarkRuleContext ctx,
            SkylarkList outputs,
            SkylarkList inputs,
            Object executableUnchecked,
            SkylarkList arguments,
            Object mnemonicUnchecked,
            Object commandUnchecked,
            Object progressMessage,
            Boolean useDefaultShellEnv,
            Object envUnchecked,
            Object executionRequirementsUnchecked,
            Object inputManifestsUnchecked,
            Location loc)
            throws EvalException, ConversionException {
          SpawnAction.Builder builder = new SpawnAction.Builder();
          // TODO(bazel-team): builder still makes unnecessary copies of inputs, outputs and args.
          boolean hasCommand = commandUnchecked != Runtime.NONE;
          builder.addInputs(inputs.getContents(Artifact.class, "inputs"));
          builder.addOutputs(outputs.getContents(Artifact.class, "outputs"));
          if (hasCommand && arguments.size() > 0) {
            // When we use a shell command, add an empty argument before other arguments.
            //   e.g.  bash -c "cmd" '' 'arg1' 'arg2'
            // bash will use the empty argument as the value of $0 (which we don't care about).
            // arg1 and arg2 will be $1 and $2, as a user exects.
            builder.addArgument("");
          }
          builder.addArguments(arguments.getContents(String.class, "arguments"));
          if (executableUnchecked != Runtime.NONE) {
            if (executableUnchecked instanceof Artifact) {
              Artifact executable = (Artifact) executableUnchecked;
              builder.addInput(executable);
              FilesToRunProvider provider = ctx.getExecutableRunfiles(executable);
              if (provider == null) {
                builder.setExecutable(executable);
              } else {
                builder.setExecutable(provider);
              }
            } else if (executableUnchecked instanceof PathFragment) {
              builder.setExecutable((PathFragment) executableUnchecked);
            } else {
              throw new EvalException(
                  loc,
                  "expected file or PathFragment for "
                      + "executable but got "
                      + EvalUtils.getDataTypeName(executableUnchecked)
                      + " instead");
            }
          }
          if ((commandUnchecked == Runtime.NONE) == (executableUnchecked == Runtime.NONE)) {
            throw new EvalException(
                loc, "You must specify either 'command' or 'executable' argument");
          }
          if (hasCommand) {
            if (commandUnchecked instanceof String) {
              builder.setShellCommand((String) commandUnchecked);
            } else if (commandUnchecked instanceof SkylarkList) {
              SkylarkList commandList = (SkylarkList) commandUnchecked;
              if (commandList.size() < 3) {
                throw new EvalException(loc, "'command' list has to be of size at least 3");
              }
              builder.setShellCommand(commandList.getContents(String.class, "command"));
            } else {
              throw new EvalException(
                  loc,
                  "expected string or list of strings for "
                      + "command instead of "
                      + EvalUtils.getDataTypeName(commandUnchecked));
            }
          }

          // The actual command can refer to an executable from the inputs, which could
          // require some runfiles. Consequently, we add the runfiles of every executable
          // input file that is in HOST configuration to the action as a precaution.
          addRequiredIndirectRunfiles(ctx, builder);

          if (mnemonicUnchecked != Runtime.NONE) {
            builder.setMnemonic((String) mnemonicUnchecked);
          }
          if (envUnchecked != Runtime.NONE) {
            builder.setEnvironment(
                ImmutableMap.copyOf(
                    SkylarkDict.castSkylarkDictOrNoneToDict(
                        envUnchecked, String.class, String.class, "env")));
          }
          if (progressMessage != Runtime.NONE) {
            builder.setProgressMessage((String) progressMessage);
          }
          if (EvalUtils.toBoolean(useDefaultShellEnv)) {
            builder.useDefaultShellEnvironment();
          }
          if (executionRequirementsUnchecked != Runtime.NONE) {
            builder.setExecutionInfo(
                ImmutableMap.copyOf(
                    SkylarkDict.castSkylarkDictOrNoneToDict(
                        executionRequirementsUnchecked,
                        String.class,
                        String.class,
                        "execution_requirements")));
          }
          if (inputManifestsUnchecked != Runtime.NONE) {
            for (Map.Entry<PathFragment, Artifact> entry :
                     SkylarkDict.castSkylarkDictOrNoneToDict(
                         inputManifestsUnchecked,
                         PathFragment.class,
                         Artifact.class,
                         "input manifest file map")
                     .entrySet()) {
              builder.addInputManifest(entry.getValue(), entry.getKey());
            }
          }
          // Always register the action
          ctx.getRuleContext().registerAction(builder.build(ctx.getRuleContext()));
          return Runtime.NONE;
        }
      };

  /**
   * Adds the runfiles of the given input files to the action builder when they are executable and
   * in HOST configuration.
   */
  private static void addRequiredIndirectRunfiles(
      SkylarkRuleContext ctx, SpawnAction.Builder builder) {
    RuleContext ruleContext = ctx.getRuleContext();
    AttributeMap attrMap = ruleContext.attributes();

    for (String attrName : attrMap.getAttributeNames()) {
      Attribute attr = attrMap.getAttributeDefinition(attrName);
      if (attr.isExecutable()
          && (attr.getConfigurationTransition() == ConfigurationTransition.HOST)) {
        FilesToRunProvider prov = ruleContext.getExecutablePrerequisite(attrName, Mode.HOST);
        if (prov != null) {
          builder.addTool(prov);
        }
      }
    }
  }

  @SkylarkSignature(name = "expand_location",
      doc =
      "Expands the given string so that all labels are replaced with the location "
      + "of their target file(s). Currently, the algorithm uses output, srcs, deps, "
      + "tools and data attributes for looking up mappings from label to locations.",
      objectType = SkylarkRuleContext.class, returnType = String.class,
      mandatoryPositionals = {
          @Param(name = "self", type = SkylarkRuleContext.class, doc = "this context"),
          @Param(name = "input", type = String.class, doc = "string to be expanded"),
      },
      optionalPositionals = {
          @Param(name = "targets", type = SkylarkList.class,
              generic1 = AbstractConfiguredTarget.class, defaultValue = "[]",
              doc = "list of targets for additional lookup information"),
      },
      useLocation = true, useEnvironment = true)
  private static final BuiltinFunction expandLocation = new BuiltinFunction("expand_location") {
    @SuppressWarnings("unused")
    public String invoke(SkylarkRuleContext ctx, String input, SkylarkList targets,
        Location loc, Environment env) throws EvalException {
      try {
        return new LocationExpander(ctx.getRuleContext(),
                makeLabelMap(targets.getContents(AbstractConfiguredTarget.class, "targets")), false)
            .expand(input);
      } catch (IllegalStateException ise) {
        throw new EvalException(loc, ise);
      }
    }
  };

  /**
   * 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<AbstractConfiguredTarget> knownLabels) {
    ImmutableMap.Builder<Label, ImmutableCollection<Artifact>> builder = ImmutableMap.builder();

    for (AbstractConfiguredTarget current : knownLabels) {
      builder.put(
          current.getLabel(),
          ImmutableList.copyOf(current.getProvider(FileProvider.class).getFilesToBuild()));
    }

    return builder.build();
  }

  // TODO(bazel-team): improve this method to be more memory friendly
  @SkylarkSignature(name = "file_action",
      doc = "Creates a file write action.",
      objectType = SkylarkRuleContext.class,
      returnType = FileWriteAction.class,
      mandatoryPositionals = {
        @Param(name = "self", type = SkylarkRuleContext.class, doc = "this context"),
        @Param(name = "output", type = Artifact.class, doc = "the output file"),
        @Param(name = "content", type = String.class, doc = "the contents of the file")},
      optionalPositionals = {
        @Param(name = "executable", type = Boolean.class, defaultValue = "False",
            doc = "whether the output file should be executable (default is False)")})
  private static final BuiltinFunction createFileWriteAction =
      new BuiltinFunction("file_action") {
        public FileWriteAction invoke(SkylarkRuleContext ctx,
            Artifact output, String content, Boolean executable)
            throws EvalException, ConversionException {
          FileWriteAction action = new FileWriteAction(
              ctx.getRuleContext().getActionOwner(), output, content, executable);
          ctx.getRuleContext().registerAction(action);
          return action;
        }
      };

  @SkylarkSignature(name = "empty_action",
      doc =
      "Creates an empty action that neither executes a command nor produces any "
      + "output, but that is useful for inserting 'extra actions'.",
      objectType = SkylarkRuleContext.class, returnType = Runtime.NoneType.class,
      mandatoryPositionals = {
          @Param(name = "self", type = SkylarkRuleContext.class, doc = "this context"),
      },
      mandatoryNamedOnly = {
          @Param(name = "mnemonic", type = String.class, defaultValue = "None",
          doc = "a one-word description of the action, e.g. CppCompile or GoLink"),
      },
      optionalNamedOnly = {
          @Param(name = "inputs", type = SkylarkList.class, generic1 = Artifact.class,
              defaultValue = "[]", doc = "list of the input files of the action"),
      })
  private static final BuiltinFunction createEmptyAction = new BuiltinFunction("empty_action") {
    @SuppressWarnings("unused")
    public Runtime.NoneType invoke(SkylarkRuleContext ctx, String mnemonic, SkylarkList inputs)
        throws EvalException, ConversionException {
      RuleContext ruleContext = ctx.getRuleContext();
      Action action = new PseudoAction<SpawnInfo>(generateUuid(ruleContext),
          ruleContext.getActionOwner(), convertInputs(inputs), generateDummyOutputs(ruleContext),
          mnemonic, SpawnInfo.spawnInfo, createEmptySpawnInfo());
      ruleContext.registerAction(action);

      return Runtime.NONE;
    }

    private NestedSet<Artifact> convertInputs(SkylarkList inputs) throws EvalException {
      return NestedSetBuilder.<Artifact>compileOrder()
          .addAll(inputs.getContents(Artifact.class, "inputs")).build();
    }

    protected UUID generateUuid(RuleContext ruleContext) {
      return UUID.nameUUIDFromBytes(
          String.format("empty action %s", ruleContext.getLabel())
              .getBytes(StandardCharsets.UTF_8));
    }

    protected ImmutableList<Artifact> generateDummyOutputs(RuleContext ruleContext) {
      return ImmutableList.of(PseudoAction.getDummyOutput(ruleContext));
    }

    protected SpawnInfo createEmptySpawnInfo() {
      return SpawnInfo.newBuilder().build();
    }
  };

  @SkylarkSignature(name = "template_action",
      doc = "Creates a template expansion action.",
      objectType = SkylarkRuleContext.class,
      returnType = TemplateExpansionAction.class,
      mandatoryPositionals = {
        @Param(name = "self", type = SkylarkRuleContext.class, doc = "this context")},
      mandatoryNamedOnly = {
        @Param(name = "template", type = Artifact.class,
            doc = "the template file"),
        @Param(name = "output", type = Artifact.class,
            doc = "the output file"),
        @Param(name = "substitutions", type = SkylarkDict.class,
            doc = "substitutions to make when expanding the template")},
      optionalNamedOnly = {
        @Param(name = "executable", type = Boolean.class,
            doc = "whether the output file should be executable (default is False)")})
  private static final BuiltinFunction createTemplateAction =
      new BuiltinFunction("template_action", Arrays.<Object>asList(false)) {
        public TemplateExpansionAction invoke(SkylarkRuleContext ctx, Artifact template,
            Artifact output, SkylarkDict<?, ?> substitutionsUnchecked, Boolean executable)
            throws EvalException, ConversionException {
          ImmutableList.Builder<Substitution> substitutionsBuilder = ImmutableList.builder();
          for (Map.Entry<String, String> substitution : substitutionsUnchecked.getContents(
              String.class, String.class, "substitutions").entrySet()) {
            // ParserInputSource.create(Path) uses Latin1 when reading BUILD files, which might
            // contain UTF-8 encoded symbols as part of template substitution.
            // As a quick fix, the substitution values are corrected before being passed on.
            // In the long term, fixing ParserInputSource.create(Path) would be a better approach.
            substitutionsBuilder.add(Substitution.of(
                substitution.getKey(), convertLatin1ToUtf8(substitution.getValue())));
          }
          TemplateExpansionAction action = new TemplateExpansionAction(
              ctx.getRuleContext().getActionOwner(),
              template,
              output,
              substitutionsBuilder.build(),
              executable);
          ctx.getRuleContext().registerAction(action);
          return action;
        }
      };

  /**
   * Returns the proper UTF-8 representation of a String that was erroneously read using Latin1.
   * @param latin1 Input string
   * @return The input string, UTF8 encoded
   */
  private static String convertLatin1ToUtf8(String latin1) {
    return new String(latin1.getBytes(StandardCharsets.ISO_8859_1), StandardCharsets.UTF_8);
  }

  /**
   * A built in Skylark helper function to access the
   * Transitive info providers of Transitive info collections.
   */
  @SkylarkSignature(name = "provider",
      doc = "Returns the transitive info provider provided by the target.",
      mandatoryPositionals = {
        @Param(name = "target", type = TransitiveInfoCollection.class,
            doc = "the configured target which provides the provider"),
        @Param(name = "type", type = String.class, doc = "the class type of the provider")},
      useLocation = true)
  private static final BuiltinFunction provider = new BuiltinFunction("provider") {
      public Object invoke(TransitiveInfoCollection target, String type,
          Location loc) throws EvalException {
      try {
        Class<?> classType = SkylarkRuleContext.classCache.get(type);
        Class<? extends TransitiveInfoProvider> convertedClass =
            classType.asSubclass(TransitiveInfoProvider.class);
        Object result = target.getProvider(convertedClass);
        return result == null ? Runtime.NONE : result;
      } catch (ExecutionException e) {
        throw new EvalException(loc, "Unknown class type " + type);
      } catch (ClassCastException e) {
        throw new EvalException(loc, "Not a TransitiveInfoProvider " + type);
      }
    }
  };

  // TODO(bazel-team): Remove runfile states from Skylark.
  @SkylarkSignature(name = "runfiles",
      doc = "Creates a runfiles object.",
      objectType = SkylarkRuleContext.class,
      returnType = Runfiles.class,
      mandatoryPositionals = {
        @Param(name = "self", type = SkylarkRuleContext.class, doc = "This context.")},
      optionalPositionals = {
        @Param(name = "files", type = SkylarkList.class, generic1 = Artifact.class,
            defaultValue = "[]", doc = "The list of files to be added to the runfiles."),
        // TODO(bazel-team): If we have a memory efficient support for lazy list containing
        // NestedSets we can remove this and just use files = [file] + list(set)
        // Also, allow empty set for init
        @Param(name = "transitive_files", type = SkylarkNestedSet.class, generic1 = Artifact.class,
            noneable = true, defaultValue = "None",
            doc = "The (transitive) set of files to be added to the runfiles."),
        @Param(name = "collect_data", type = Boolean.class, defaultValue = "False",
            doc = "Whether to collect the data "
            + "runfiles from the dependencies in srcs, data and deps attributes."),
        @Param(name = "collect_default", type = Boolean.class, defaultValue = "False",
            doc = "Whether to collect the default "
            + "runfiles from the dependencies in srcs, data and deps attributes."),
        @Param(name = "symlinks", type = SkylarkDict.class, defaultValue = "{}",
            doc = "The map of symlinks to be added to the runfiles, prefixed by workspace name."),
        @Param(name = "root_symlinks", type = SkylarkDict.class, defaultValue = "{}",
            doc = "The map of symlinks to be added to the runfiles.")},
      useLocation = true)
  private static final BuiltinFunction runfiles = new BuiltinFunction("runfiles") {
    public Runfiles invoke(SkylarkRuleContext ctx, SkylarkList files, Object transitiveFiles,
        Boolean collectData, Boolean collectDefault,
        SkylarkDict<?, ?> symlinks, SkylarkDict<?, ?> rootSymlinks,
        Location loc) throws EvalException, ConversionException {
      Runfiles.Builder builder = new Runfiles.Builder(
          ctx.getRuleContext().getWorkspaceName(),
          ctx.getConfiguration().legacyExternalRunfiles());
      boolean checkConflicts = false;
      if (EvalUtils.toBoolean(collectData)) {
        builder.addRunfiles(ctx.getRuleContext(), RunfilesProvider.DATA_RUNFILES);
      }
      if (EvalUtils.toBoolean(collectDefault)) {
        builder.addRunfiles(ctx.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(new PathFragment(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(new PathFragment(entry.getKey()), entry.getValue());
        }
      }
      Runfiles runfiles = builder.build();
      if (checkConflicts) {
        runfiles.setConflictPolicy(Runfiles.ConflictPolicy.ERROR);
      }
      return runfiles;
    }
  };


  // TODO(bazel-team): find a better way to typecheck this argument.
  @SuppressWarnings("unchecked")
  private static Map<Label, Iterable<Artifact>> checkLabelDict(
      Map<?, ?> labelDict, Location loc)
      throws EvalException {
    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));
      }
      Object val = entry.getValue();
      if (!(val instanceof Iterable)) {
        throw new EvalException(
            loc, Printer.format("invalid value %r in 'label_dict'", val));
      }
      for (Object file : (Iterable) val) {
        if (!(file instanceof Artifact)) {
          throw new EvalException(
              loc, Printer.format("invalid value %r in 'label_dict'", val));
        }
      }
    }
    return (Map<Label, Iterable<Artifact>>) labelDict;
  }

  /** 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";

  @SkylarkSignature(
    name = "resolve_command",
    doc = "Experimental."
    + "Returns a tuple (inputs, command, input_manifests) of the list of resolved inputs, "
    + "the argv list for the resolved command, and "
    + "the dict mapping locations to runfiles required to run the command, "
    + "all of them suitable for passing as the same-named arguments of the ctx.action method.",
    objectType = SkylarkRuleContext.class,
    returnType = Tuple.class,
    mandatoryPositionals = {
      @Param(name = "self", type = SkylarkRuleContext.class, doc = "this RuleContext")
    },
    optionalNamedOnly = {
      @Param(
        name = "command",
        type = String.class, // string
        defaultValue = "''",
        doc = "command to resolve"
      ),
      @Param(
        name = "attribute",
        type = String.class, // string
        noneable = true,
        doc = "name of the associated attribute for which to issue an error, or None"
      ),
      @Param(
        name = "expand_locations",
        type = Boolean.class,
        defaultValue = "False",
        doc = "shall we expand $(location) variables?"
      ),
      @Param(
        name = "make_variables",
        type = SkylarkDict.class, // dict(string, string)
        noneable = true,
        doc = "make variables to expand, or None"
      ),
      @Param(
        name = "tools",
        defaultValue = "[]",
        type = SkylarkList.class,
        generic1 = TransitiveInfoCollection.class,
        doc = "list of tools (list of targets)"
      ),
      @Param(
        name = "label_dict",
        type = SkylarkDict.class,
        defaultValue = "{}",
        doc =
            "dictionary of resolved labels and the corresponding list of Files "
        + "(a dict of Label : list of Files)"
      ),
      @Param(
        name = "execution_requirements",
        type = SkylarkDict.class,
        defaultValue = "{}",
        doc =
            "information for scheduling the action to resolve this command."
                + " See [tags](/docs/be/common-definitions.html#common.tags) for useful keys."
      ),
    },
    useLocation = true, useEnvironment = true
  )
  private static final BuiltinFunction resolveCommand =
      new BuiltinFunction("resolve_command") {
        @SuppressWarnings("unchecked")
        public Tuple<Object> invoke(
            SkylarkRuleContext ctx,
            String command,
            Object attributeUnchecked,
            Boolean expandLocations,
            Object makeVariablesUnchecked,
            SkylarkList tools,
            SkylarkDict<?, ?> labelDictUnchecked,
            SkylarkDict<?, ?> executionRequirementsUnchecked,
            Location loc,
            Environment env)
            throws ConversionException, EvalException {
          Label ruleLabel = ctx.getLabel();
          Map<Label, Iterable<Artifact>> labelDict = checkLabelDict(labelDictUnchecked, loc);
          // The best way to fix this probably is to convert CommandHelper to Skylark.
          CommandHelper helper = new CommandHelper(
              ctx.getRuleContext(),
              tools.getContents(TransitiveInfoCollection.class, "tools"),
              ImmutableMap.copyOf(labelDict));
          String attribute =
              Type.STRING.convertOptional(attributeUnchecked, "attribute", ruleLabel);
          if (expandLocations) {
            command = helper.resolveCommandAndExpandLabels(
                command, attribute, false, false);
          }
          if (!EvalUtils.isNullOrNone(makeVariablesUnchecked)) {
            Map<String, String> makeVariables = Type.STRING_DICT.convert(
                makeVariablesUnchecked, "make_variables", ruleLabel);
            command = ctx.expandMakeVariables(attribute, command, makeVariables);
          }
          List<Artifact> inputs = new ArrayList<>();
          inputs.addAll(helper.getResolvedTools());

          ImmutableMap<String, String> executionRequirements = ImmutableMap.copyOf(
              SkylarkDict.castSkylarkDictOrNoneToDict(
                    executionRequirementsUnchecked,
                    String.class,
                    String.class,
                    "execution_requirements"));
          List<String> argv =
              helper.buildCommandLine(command, inputs, SCRIPT_SUFFIX, executionRequirements);
          return Tuple.<Object>of(
              new MutableList(inputs, env),
              new MutableList(argv, env),
              helper.getRemoteRunfileManifestMap());
        }
      };

  static {
    SkylarkSignatureProcessor.configureSkylarkFunctions(SkylarkRuleImplementationFunctions.class);
  }
}