src/main/java/com/google/devtools/build/lib/packages/StructProvider.java

// Copyright 2018 The Bazel Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.google.devtools.build.lib.packages;

import com.google.common.collect.ImmutableMap;
import com.google.devtools.build.lib.events.Location;
import com.google.devtools.build.lib.skylarkbuildapi.StructApi;
import com.google.devtools.build.lib.syntax.EvalException;
import com.google.devtools.build.lib.syntax.SkylarkDict;
import java.util.Map;

/**
 * The provider for the built-in type {@code struct}.
 *
 * <p>Its singleton instance is {@link StructProvider#STRUCT}.
 */
public final class StructProvider extends BuiltinProvider<StructImpl>
    implements StructApi.StructProviderApi {

  /** "struct" function. */
  public static final StructProvider STRUCT = new StructProvider();

  StructProvider() {
    super("struct", StructImpl.class);
  }

  @Override
  public StructImpl createStruct(SkylarkDict<?, ?> kwargs, Location loc) throws EvalException {
    Map<String, Object> kwargsMap = kwargs.getContents(String.class, Object.class, "kwargs");
    if (kwargsMap.containsKey("to_json")) {
      throw new EvalException(loc, "cannot override built-in struct function 'to_json'");
    }
    if (kwargsMap.containsKey("to_proto")) {
      throw new EvalException(loc, "cannot override built-in struct function 'to_proto'");
    }
    return SkylarkInfo.createSchemaless(this, kwargsMap, loc);
  }

  /**
   * Creates a struct with the given field values and message format for unknown fields.
   *
   * <p>The custom message is useful for objects that have fields but aren't exactly used as
   * providers, such as the {@code native} object, and the struct fields of {@code ctx} like
   * {@code ctx.attr}.
   * */
  public SkylarkInfo create(
      Map<String, Object> values, String errorMessageFormatForUnknownField) {
    return SkylarkInfo.createSchemalessWithCustomMessage(
        this, values, errorMessageFormatForUnknownField);
  }

  /** Creates an empty struct with the given location. */
  public SkylarkInfo createEmpty(Location loc) {
    return SkylarkInfo.createSchemaless(this, ImmutableMap.of(), loc);
  }
}