src/main/java/com/google/devtools/build/lib/rules/config/ConfigRules.java

// Copyright 2017 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.config;

import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.analysis.BaseRuleClasses;
import com.google.devtools.build.lib.analysis.ConfiguredRuleClassProvider;
import com.google.devtools.build.lib.analysis.ConfiguredRuleClassProvider.RuleSet;
import com.google.devtools.build.lib.analysis.starlark.StarlarkConfig;
import com.google.devtools.build.lib.rules.config.ConfigFeatureFlagTaggedTrimmingTransitionFactory.ConfigFeatureFlagTaggedTrimmingTransition;
import com.google.devtools.build.lib.rules.core.CoreRules;
import com.google.devtools.build.lib.rules.platform.PlatformRules;
import com.google.devtools.build.lib.starlarkbuildapi.config.ConfigBootstrap;

/**
 * Set of rules to specify or manipulate configuration settings.
 */
public final class ConfigRules implements RuleSet {
  public static final ConfigRules INSTANCE = new ConfigRules();

  private ConfigRules() {
    // Use the static INSTANCE field instead.
  }

  @Override
  public void init(ConfiguredRuleClassProvider.Builder builder) {
    builder.addTrimmingTransitionFactory(
        new ConfigFeatureFlagTaggedTrimmingTransitionFactory(BaseRuleClasses.TAGGED_TRIMMING_ATTR));

    // This implementation trims all feature flags out of toolchains. This is performant assuming
    // toolchains don't need to read feature flags (which should be practically the case). We can
    // turn this into a no-op should that need ever arise (and pay the added performance cost).
    builder.setToolchainTaggedTrimmingTransition(ConfigFeatureFlagTaggedTrimmingTransition.EMPTY);

    builder.addRuleDefinition(new ConfigRuleClasses.ConfigBaseRule());
    builder.addRuleDefinition(new ConfigRuleClasses.ConfigSettingRule());
    builder.addConfigurationFragment(ConfigFeatureFlagConfiguration.class);

    builder.addRuleDefinition(new ConfigRuleClasses.ConfigFeatureFlagRule());
    builder.addStarlarkBootstrap(
        new ConfigBootstrap(
            new ConfigStarlarkCommon(), new StarlarkConfig(), new ConfigGlobalLibrary()));
  }

  @Override
  public ImmutableList<RuleSet> requires() {
    return ImmutableList.of(CoreRules.INSTANCE, PlatformRules.INSTANCE);
  }
}