src/main/java/com/google/devtools/build/lib/skyframe/PrecomputedValue.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.skyframe;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.MoreObjects;
import com.google.common.base.Preconditions;
import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import com.google.devtools.build.lib.packages.Package.ConfigSettingVisibilityPolicy;
import com.google.devtools.build.lib.packages.RuleVisibility;
import com.google.devtools.build.lib.pkgcache.PackageOptions.LazyMacroExpansionPackages;
import com.google.devtools.build.lib.pkgcache.PathPackageLocator;
import com.google.devtools.build.lib.skyframe.serialization.VisibleForSerialization;
import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
import com.google.devtools.build.skyframe.AbstractSkyKey;
import com.google.devtools.build.skyframe.Differencer.DiffWithDelta.Delta;
import com.google.devtools.build.skyframe.Injectable;
import com.google.devtools.build.skyframe.SkyFunction;
import com.google.devtools.build.skyframe.SkyFunctionName;
import com.google.devtools.build.skyframe.SkyKey;
import com.google.devtools.build.skyframe.SkyValue;
import java.util.Map;
import java.util.UUID;
import javax.annotation.Nullable;
import net.starlark.java.eval.StarlarkSemantics;

/**
 * A value that represents something computed outside of the skyframe framework. These values are
 * "precomputed" from skyframe's perspective and so the graph needs to be prepopulated with them
 * (e.g. via injection).
 */
public final class PrecomputedValue implements SkyValue {
  /**
   * An externally-injected precomputed value. Exists so that modules can inject precomputed values
   * into Skyframe's graph.
   *
   * @see com.google.devtools.build.lib.runtime.BlazeModule#getPrecomputedValues
   */
  public static final class Injected {
    private final Precomputed<?> precomputed;
    private final Supplier<?> supplier;

    private Injected(Precomputed<?> precomputed, Supplier<?> supplier) {
      this.precomputed = precomputed;
      this.supplier = supplier;
    }

    public void inject(Injectable injectable) {
      injectable.inject(precomputed.key, Delta.justNew(new PrecomputedValue(supplier.get())));
    }

    public SkyKey getKey() {
      return precomputed.getKey();
    }

    @Override
    public String toString() {
      return precomputed + ": " + supplier.get();
    }
  }

  public static <T> Injected injected(Precomputed<T> precomputed, Supplier<T> value) {
    return new Injected(precomputed, value);
  }

  public static <T> Injected injected(Precomputed<T> precomputed, T value) {
    return new Injected(precomputed, Suppliers.ofInstance(value));
  }

  public static final Precomputed<RuleVisibility> DEFAULT_VISIBILITY =
      new Precomputed<>("default_visibility");

  public static final Precomputed<ConfigSettingVisibilityPolicy> CONFIG_SETTING_VISIBILITY_POLICY =
      new Precomputed<>("config_setting_visibility_policy");

  public static final Precomputed<StarlarkSemantics> STARLARK_SEMANTICS =
      new Precomputed<>("starlark_semantics");

  public static final Precomputed<UUID> BUILD_ID = Precomputed.createUnshareable("build_id");

  public static final Precomputed<Map<String, String>> ACTION_ENV = new Precomputed<>("action_env");

  public static final Precomputed<PathPackageLocator> PATH_PACKAGE_LOCATOR =
      new Precomputed<>("path_package_locator");

  public static final Precomputed<Boolean> REMOTE_EXECUTION_ENABLED =
      new Precomputed<>("remote_execution_enabled");

  public static final Precomputed<LazyMacroExpansionPackages> LAZY_MACRO_EXPANSION_PACKAGES =
      new Precomputed<>("lazy_macro_expansion_packages");

  /**
   * A marker Skyframe dependency for a configured target that may behave differently due to {@code
   * --stamp=true}, even if it does not own a stamped action.
   *
   * <p>Examples are:
   *
   * <ul>
   *   <li>When a starlark transition reads {@code //command_line_option:stamp} as an input.
   *   <li>When a starlark transition sets {@code //command_line_option:stamp} as an output (since
   *       then dependencies may have a different output path in --stamp vs --nostamp).
   *   <li>A {@code config_setting} that matches on the value of {@code --stamp}.
   * </ul>
   *
   * <p>The value is irrelevant. Its {@link Injected#getKey} is just a marker dependency.
   */
  public static final Injected STAMP_SETTING_MARKER =
      injected(new Precomputed<>("stamp_setting_marker"), Boolean.TRUE);

  private final Object value;

  @VisibleForTesting
  public PrecomputedValue(Object value) {
    this.value = Preconditions.checkNotNull(value);
  }

  /** Returns the value of the variable. */
  public Object get() {
    return value;
  }

  @Override
  public int hashCode() {
    return value.hashCode();
  }

  @Override
  public boolean equals(Object obj) {
    if (!(obj instanceof PrecomputedValue other)) {
      return false;
    }
    return value.equals(other.value);
  }

  @Override
  public String toString() {
    return "<BuildVariable " + value + ">";
  }

  /**
   * A helper object corresponding to a variable in Skyframe.
   *
   * <p>Instances do not have internal state.
   */
  public static final class Precomputed<T> {
    private final SkyKey key;

    public Precomputed(String key) {
      this(key, /* shareable= */ true);
    }

    private Precomputed(String key, boolean shareable) {
      this.key = shareable ? Key.create(key) : UnshareableKey.create(key);
    }

    public static <T> Precomputed<T> createUnshareable(String key) {
      return new Precomputed<>(key, /* shareable= */ false);
    }

    public SkyKey getKey() {
      return key;
    }

    /**
     * Retrieves the value of this variable from Skyframe.
     *
     * <p>If the value was not set, an exception will be raised.
     */
    @Nullable
    @SuppressWarnings("unchecked")
    public T get(SkyFunction.Environment env) throws InterruptedException {
      PrecomputedValue value = (PrecomputedValue) env.getValue(key);
      if (value == null) {
        return null;
      }
      return (T) value.get();
    }

    /** Injects a new variable value. */
    public void set(Injectable injectable, T value) {
      injectable.inject(key, Delta.justNew(new PrecomputedValue(value)));
    }

    @Override
    public String toString() {
      return MoreObjects.toStringHelper(this)
          .add("key", key)
          .add("shareable", key.valueIsShareable())
          .toString();
    }
  }

  /** {@link com.google.devtools.build.skyframe.SkyKey} for {@code PrecomputedValue}. */
  @AutoCodec
  public static final class Key extends AbstractSkyKey<String> {
    private static final SkyKeyInterner<Key> interner = SkyKey.newInterner();

    private Key(String arg) {
      super(arg);
    }

    public static Key create(String arg) {
      return interner.intern(new Key(arg));
    }

    @VisibleForSerialization
    @AutoCodec.Interner
    static Key intern(Key key) {
      return interner.intern(key);
    }

    @Override
    public SkyFunctionName functionName() {
      return SkyFunctions.PRECOMPUTED;
    }

    @Override
    public SkyKeyInterner<Key> getSkyKeyInterner() {
      return interner;
    }
  }

  /** Unshareable version of {@link Key}. */
  @AutoCodec
  @VisibleForSerialization
  static final class UnshareableKey extends AbstractSkyKey<String> {
    private static final SkyKeyInterner<UnshareableKey> interner = SkyKey.newInterner();

    private UnshareableKey(String arg) {
      super(arg);
    }

    private static UnshareableKey create(String arg) {
      return interner.intern(new UnshareableKey(arg));
    }

    @VisibleForSerialization
    @AutoCodec.Interner
    static UnshareableKey intern(UnshareableKey unshareableKey) {
      return interner.intern(unshareableKey);
    }

    @Override
    public SkyFunctionName functionName() {
      return SkyFunctions.PRECOMPUTED;
    }

    @Override
    public boolean valueIsShareable() {
      return false;
    }

    @Override
    public SkyKeyInterner<UnshareableKey> getSkyKeyInterner() {
      return interner;
    }
  }
}