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

// Copyright 2015 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.base.Preconditions;
import com.google.common.collect.ImmutableSet;
import com.google.common.io.BaseEncoding;
import com.google.devtools.build.lib.packages.Attribute.ComputedDefault;
import com.google.devtools.build.lib.query2.proto.proto2api.Build;
import javax.annotation.Nullable;

/** Serialize a {@link Rule} as its protobuf representation. */
public class RuleFormatter {

  // Starlark doesn't support defining rule classes with ComputedDefault attributes. Therefore, the
  // only ComputedDefault attributes we expect to see for Starlark-defined rule classes are
  // those declared in those rule classes' natively defined base rule classes, which are:
  //
  // 1. The "timeout" attribute in SkylarkRuleClassFunctions.testBaseRule
  // 2. The "deprecation" attribute in BaseRuleClasses.commonCoreAndSkylarkAttributes
  // 3. The "testonly" attribute in BaseRuleClasses.commonCoreAndSkylarkAttributes
  private static final ImmutableSet<String> SKYLARK_RULE_CLASS_COMPUTED_DEFAULT_ATTRIBUTES =
      ImmutableSet.of("timeout", "deprecation", "testonly");

  public static Build.Rule.Builder serializeRule(Rule rule) {
    Build.Rule.Builder builder = Build.Rule.newBuilder();
    builder.setName(rule.getLabel().getName());
    builder.setRuleClass(rule.getRuleClass());
    builder.setPublicByDefault(rule.getRuleClassObject().isPublicByDefault());

    RawAttributeMapper rawAttributeMapper = RawAttributeMapper.of(rule);
    boolean isSkylark = rule.getRuleClassObject().isStarlark();

    if (isSkylark) {
      builder.setSkylarkEnvironmentHashCode(
          // hexify
          BaseEncoding.base16()
              .lowerCase()
              .encode(
                  Preconditions.checkNotNull(
                      rule.getRuleClassObject().getRuleDefinitionEnvironmentDigest(), rule)));
    }
    for (Attribute attr : rule.getAttributes()) {
      Object rawAttributeValue = rawAttributeMapper.getRawAttributeValue(rule, attr);
      boolean isExplicit = rule.isAttributeValueExplicitlySpecified(attr);

      if (!isSkylark && !isExplicit) {
        // If the rule class is native (i.e. not Starlark-defined), then we can skip serialization
        // of implicit attribute values. The native rule class can provide the same default value
        // for the attribute after deserialization.
        continue;
      }

      Object valueToSerialize;
      if (isExplicit) {
        valueToSerialize = rawAttributeValue;
      } else if (rawAttributeValue instanceof ComputedDefault) {
        // If the rule class is Starlark-defined (i.e. rule.getRuleClassObject().isSkylark() is
        // true), and the attribute has a ComputedDefault value, then we must serialize what it
        // evaluates to. The Starlark-defined ComputedDefault function won't be available after
        // deserialization due to Starlark's non-serializability.
        valueToSerialize = evaluateSkylarkComputedDefault(rawAttributeMapper, attr);
        if (valueToSerialize == null) {
          continue;
        }
      } else {
        // If the rule class is Starlark-defined and the attribute value is implicit, then we
        // must serialize it. The Starlark-defined rule class won't be available after
        // deserialization due to Starlark's non-serializability.
        valueToSerialize = rawAttributeValue;
      }

      builder.addAttribute(
          AttributeFormatter.getAttributeProto(
              attr,
              valueToSerialize,
              isExplicit,
              /*encodeBooleanAndTriStateAsIntegerAndString=*/ false));
    }
    return builder;
  }

  /**
   * Evaluates a {@link ComputedDefault} attribute value for a {@link Rule} with a Starlark-defined
   * {@link RuleClass}.
   *
   * <p>We can't serialize ComputedDefault attributes defined in Starlark, because those can depend
   * on other attributes which are configurable.
   *
   * <p>For a few attributes ({@link #SKYLARK_RULE_CLASS_COMPUTED_DEFAULT_ATTRIBUTES}), we know for
   * certain that they don't have dependencies on other attributes which are configurable, so they
   * can be evaluated here without loss of fidelity.
   *
   * <p>The {@link RawAttributeMapper#get} method, inherited from {@link AbstractAttributeMapper},
   * evaluates the {@link ComputedDefault} function, so we use that, after verifying the attribute's
   * name is expected.
   *
   * @return the attribute's default value if we know it can be safely serialized, or null
   *     otherwise.
   */
  @Nullable
  private static Object evaluateSkylarkComputedDefault(
      RawAttributeMapper rawAttributeMapper, Attribute attr) {
    if (SKYLARK_RULE_CLASS_COMPUTED_DEFAULT_ATTRIBUTES.contains(attr.getName())) {
      return rawAttributeMapper.get(attr.getName(), attr.getType());
    }
    return null;
  }
}