src/main/java/com/google/devtools/build/lib/rules/Alias.java

// Copyright 2016 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 static com.google.devtools.build.lib.packages.Attribute.ANY_RULE;
import static com.google.devtools.build.lib.packages.Attribute.attr;
import static com.google.devtools.build.lib.packages.BuildType.LABEL;

import com.google.common.collect.ImmutableMap;
import com.google.devtools.build.lib.actions.MutableActionGraph.ActionConflictException;
import com.google.devtools.build.lib.analysis.AliasProvider;
import com.google.devtools.build.lib.analysis.BaseRuleClasses;
import com.google.devtools.build.lib.analysis.ConfiguredTarget;
import com.google.devtools.build.lib.analysis.RuleConfiguredTargetFactory;
import com.google.devtools.build.lib.analysis.RuleContext;
import com.google.devtools.build.lib.analysis.RuleDefinition;
import com.google.devtools.build.lib.analysis.RuleDefinitionEnvironment;
import com.google.devtools.build.lib.analysis.VisibilityProvider;
import com.google.devtools.build.lib.analysis.VisibilityProviderImpl;
import com.google.devtools.build.lib.analysis.configuredtargets.RuleConfiguredTarget.Mode;
import com.google.devtools.build.lib.packages.RuleClass;
import com.google.devtools.build.lib.packages.RuleClass.Builder;
import com.google.devtools.build.lib.util.FileTypeSet;

/**
 * Implementation of the <code>alias</code> rule.
 */
public class Alias implements RuleConfiguredTargetFactory {
  @Override
  public ConfiguredTarget create(RuleContext ruleContext)
      throws InterruptedException, RuleErrorException, ActionConflictException {
    ConfiguredTarget actual = (ConfiguredTarget) ruleContext.getPrerequisite("actual", Mode.TARGET);
    return new AliasConfiguredTarget(
        ruleContext,
        actual,
        ImmutableMap.of(
            AliasProvider.class,
            AliasProvider.fromAliasRule(ruleContext.getLabel(), actual),
            VisibilityProvider.class,
            new VisibilityProviderImpl(ruleContext.getVisibility())));
  }

  /**
   * Rule definition.
   */
  public static class AliasRule implements RuleDefinition {
    @Override
    public RuleClass build(Builder builder, RuleDefinitionEnvironment environment) {
      return builder
          /*<!-- #BLAZE_RULE(alias).ATTRIBUTE(actual) -->
          The target this alias refers to. It does not need to be a rule, it can also be an input
          file.
          <!-- #END_BLAZE_RULE.ATTRIBUTE -->*/
          .removeAttribute("licenses")
          .removeAttribute("distribs")
          .add(
              attr("actual", LABEL)
                  .allowedFileTypes(FileTypeSet.ANY_FILE)
                  .allowedRuleClasses(ANY_RULE)
                  .mandatory())
          .canHaveAnyProvider()
          // Aliases themselves do not need toolchains or an execution platform, so this is fine.
          // The actual target
          // will resolve platforms and toolchains with no issues regardless of this setting.
          .supportsPlatforms(false)
          .build();
    }

    @Override
    public Metadata getMetadata() {
      return Metadata.builder()
          .name("alias")
          .factoryClass(Alias.class)
          .ancestors(BaseRuleClasses.BaseRule.class)
          .build();
    }
  }
}

/*<!-- #BLAZE_RULE (NAME = alias, TYPE = OTHER, FAMILY = General)[GENERIC_RULE] -->

<p>
  The <code>alias</code> rule creates another name a rule can be referred to as.
</p>

<p>
  Aliasing only works for "regular" targets. In particular, <code>package_group</code>,
    <code>config_setting</code> and <code>test_suite</code> rules cannot be aliased.
</p>

<p>
  The alias rule has its own visibility declaration. In all other respects, it behaves
  like the rule it references with some minor exceptions:

  <ul>
    <li>
      Tests are not run if their alias is mentioned on the command line
    </li>
    <li>
      When defining environment groups, the aliases to <code>environment</code> rules are not
      supported. They are not supported in the <code>--target_environment</code> command line
      option, either.
    </li>
  </ul>
</p>

<h4 id="alias_example">Examples</h4>

<pre class="code">
filegroup(
    name = "data",
    srcs = ["data.txt"],
)

alias(
    name = "other",
    actual = ":data",
)
</pre>

<!-- #END_BLAZE_RULE -->*/