src/main/java/com/google/devtools/build/lib/rules/SkylarkModules.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.ImmutableList;
import com.google.devtools.build.lib.packages.SkylarkNativeModule;
import com.google.devtools.build.lib.syntax.Environment;
import com.google.devtools.build.lib.syntax.Environment.Frame;
import com.google.devtools.build.lib.syntax.Mutability;
import com.google.devtools.build.lib.syntax.Runtime;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * The basis for a Skylark Environment with all build-related modules registered.
 */
public final class SkylarkModules {

  private SkylarkModules() { }

  /**
   * The list of built in Skylark modules.
   * Documentation is generated automatically for all these modules.
   * They are also registered with the {@link Environment}.
   */
  public static final ImmutableList<Class<?>> MODULES = ImmutableList.of(
      SkylarkAttr.class,
      SkylarkCommandLine.class,
      SkylarkNativeModule.class,
      SkylarkRuleClassFunctions.class,
      SkylarkRuleImplementationFunctions.class);

  /** Global bindings for all Skylark modules */
  private static final Map<List<Class<?>>, Frame> cache = new HashMap<>();

  public static Environment.Frame getGlobals(List<Class<?>> modules) {
    if (!cache.containsKey(modules)) {
      cache.put(modules, createGlobals(modules));
    }
    return cache.get(modules);
  }

  private static Environment.Frame createGlobals(List<Class<?>> modules) {
    try (Mutability mutability = Mutability.create("SkylarkModules")) {
      Environment env = Environment.builder(mutability)
          .setSkylark()
          .setGlobals(Environment.SKYLARK)
          .build();
      for (Class<?> moduleClass : modules) {
        Runtime.registerModuleGlobals(env, moduleClass);
      }
      return env.getGlobals();
    }
  }
}