private static Artifact getExecutable(RuleContext ruleContext, Object target)
     throws EvalException {
   Artifact executable =
       ruleContext.getRule().getRuleClassObject().outputsDefaultExecutable()
           // This doesn't actually create a new Artifact just returns the one
           // created in SkylarkruleContext.
           ? ruleContext.createOutputArtifact()
           : null;
   if (target instanceof SkylarkClassObject) {
     SkylarkClassObject struct = (SkylarkClassObject) target;
     if (struct.getValue("executable") != null) {
       // We need this because of genrule.bzl. This overrides the default executable.
       executable = cast("executable", struct, Artifact.class, struct.getCreationLoc());
     }
   }
   return executable;
 }
  private static ConfiguredTarget addStructFieldsAndBuild(
      RuleContext ruleContext,
      RuleConfiguredTargetBuilder builder,
      Object target,
      Artifact executable,
      Map<String, Class<? extends TransitiveInfoProvider>> registeredProviderTypes)
      throws EvalException {
    Location loc = null;
    Runfiles statelessRunfiles = null;
    Runfiles dataRunfiles = null;
    Runfiles defaultRunfiles = null;
    if (target instanceof SkylarkClassObject) {
      SkylarkClassObject struct = (SkylarkClassObject) target;
      loc = struct.getCreationLoc();
      for (String key : struct.getKeys()) {
        if (key.equals("files")) {
          // If we specify files_to_build we don't have the executable in it by default.
          builder.setFilesToBuild(
              cast("files", struct, SkylarkNestedSet.class, Artifact.class, loc)
                  .getSet(Artifact.class));
        } else if (key.equals("runfiles")) {
          statelessRunfiles = cast("runfiles", struct, Runfiles.class, loc);
        } else if (key.equals("data_runfiles")) {
          dataRunfiles = cast("data_runfiles", struct, Runfiles.class, loc);
        } else if (key.equals("default_runfiles")) {
          defaultRunfiles = cast("default_runfiles", struct, Runfiles.class, loc);
        } else if (key.equals("output_groups")) {
          addOutputGroups(struct.getValue(key), loc, builder);
        } else if (key.equals("instrumented_files")) {
          SkylarkClassObject insStruct =
              cast("instrumented_files", struct, SkylarkClassObject.class, loc);
          Location insLoc = insStruct.getCreationLoc();
          FileTypeSet fileTypeSet = FileTypeSet.ANY_FILE;
          if (insStruct.getKeys().contains("extensions")) {
            @SuppressWarnings("unchecked")
            List<String> exts =
                cast("extensions", insStruct, SkylarkList.class, String.class, insLoc);
            if (exts.isEmpty()) {
              fileTypeSet = FileTypeSet.NO_FILE;
            } else {
              FileType[] fileTypes = new FileType[exts.size()];
              for (int i = 0; i < fileTypes.length; i++) {
                fileTypes[i] = FileType.of(exts.get(i));
              }
              fileTypeSet = FileTypeSet.of(fileTypes);
            }
          }
          List<String> dependencyAttributes = Collections.emptyList();
          if (insStruct.getKeys().contains("dependency_attributes")) {
            dependencyAttributes =
                cast("dependency_attributes", insStruct, SkylarkList.class, String.class, insLoc);
          }
          List<String> sourceAttributes = Collections.emptyList();
          if (insStruct.getKeys().contains("source_attributes")) {
            sourceAttributes =
                cast("source_attributes", insStruct, SkylarkList.class, String.class, insLoc);
          }
          InstrumentationSpec instrumentationSpec =
              new InstrumentationSpec(fileTypeSet)
                  .withSourceAttributes(sourceAttributes.toArray(new String[0]))
                  .withDependencyAttributes(dependencyAttributes.toArray(new String[0]));
          InstrumentedFilesProvider instrumentedFilesProvider =
              InstrumentedFilesCollector.collect(
                  ruleContext,
                  instrumentationSpec,
                  InstrumentedFilesCollector.NO_METADATA_COLLECTOR,
                  Collections.<Artifact>emptySet());
          builder.addProvider(InstrumentedFilesProvider.class, instrumentedFilesProvider);
        } else if (registeredProviderTypes.containsKey(key)) {
          Class<? extends TransitiveInfoProvider> providerType = registeredProviderTypes.get(key);
          TransitiveInfoProvider provider = cast(key, struct, providerType, loc);
          builder.addProvider(providerType, provider);
        } else if (key.equals("providers")) {
          Iterable iterable = cast(key, struct, Iterable.class, loc);
          for (Object o : iterable) {
            SkylarkClassObject declaredProvider =
                SkylarkType.cast(
                    o,
                    SkylarkClassObject.class,
                    loc,
                    "The value of 'providers' should be a sequence of declared providers");
            builder.addSkylarkDeclaredProvider(declaredProvider, loc);
          }
        } else if (!key.equals("executable")) {
          // We handled executable already.
          builder.addSkylarkTransitiveInfo(key, struct.getValue(key), loc);
        }
      }
    } else if (target instanceof Iterable) {
      loc = ruleContext.getRule().getRuleClassObject().getConfiguredTargetFunction().getLocation();
      for (Object o : (Iterable) target) {
        SkylarkClassObject declaredProvider =
            SkylarkType.cast(
                o,
                SkylarkClassObject.class,
                loc,
                "A return value of rule implementation function should be "
                    + "a sequence of declared providers");
        Location creationLoc = declaredProvider.getCreationLocOrNull();
        builder.addSkylarkDeclaredProvider(
            declaredProvider, creationLoc != null ? creationLoc : loc);
      }
    }

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

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

    RunfilesProvider runfilesProvider =
        statelessRunfiles != null
            ? RunfilesProvider.simple(merge(statelessRunfiles, executable, ruleContext))
            : RunfilesProvider.withData(
                // The executable doesn't get into the default runfiles if we have runfiles states.
                // This is to keep skylark 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 =
          computedDefaultRunfiles.isEmpty()
              ? null
              : RunfilesSupport.withExecutable(ruleContext, computedDefaultRunfiles, executable);
      builder.setRunfilesSupport(runfilesSupport, executable);
    }

    if (ruleContext.getRule().getRuleClassObject().isSkylarkTestable()) {
      SkylarkClassObject actions =
          ActionsProvider.create(ruleContext.getAnalysisEnvironment().getRegisteredActions());
      builder.addSkylarkDeclaredProvider(actions, loc);
    }

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