src/main/java/com/google/devtools/build/lib/actions/ActionInput.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.actions;

import com.google.devtools.build.lib.vfs.PathFragment;
import java.util.Comparator;

/**
 * Represents an input file to a build action, with an appropriate relative path.
 *
 * <p>Artifact is the only notable implementer of the interface, but the interface remains because
 * 1) some Google specific rules ship files that could be Artifacts to remote execution by
 * instantiating ad-hoc derived classes of ActionInput. 2) historically, Google C++ rules allow
 * underspecified C++ builds. For that case, we have extra logic to guess the undeclared header
 * inclusions (eg. computed inclusions). The extra logic lives in a file that is not needed for
 * remote execution, but is a dependency, and it is inserted as a non-Artifact ActionInput.
 *
 * <p>ActionInput is used as a cache "key" for ActionInputFileCache: for Artifacts, the digest/size
 * is already stored in Artifact, but for non-artifacts, we use getExecPathString to find this data
 * in a filesystem related cache.
 *
 * <p>Note: this interface defines a natural ordering but no equals, therefore there is no guarantee
 * about consistency between the two.
 */
public interface ActionInput extends Comparable<ActionInput> {

  /** Compares action input according to their exec paths. Sorts null values first. */
  @SuppressWarnings("ReferenceEquality") // "this == other" is an optimization
  Comparator<ActionInput> EXEC_PATH_COMPARATOR =
      (a, b) -> {
        if (a == b) {
          return 0;
        }
        if (a == null) {
          return -1;
        }
        if (b == null) {
          return 1;
        }
        return a.getExecPath().compareTo(b.getExecPath());
      };

  /** Returns the relative path to the input file. */
  String getExecPathString();

  /** Returns the relative path to the input file. */
  PathFragment getExecPath();

  /** The input is a symlink that is supposed to stay un-dereferenced. */
  boolean isSymlink();

  /**
   * Returns if this input's file system path includes a digest of its content. See {@link
   * com.google.devtools.build.lib.analysis.config.BuildConfiguration#useContentBasedOutputPaths}.
   */
  default boolean contentBasedPath() {
    return false;
  }

  /** Orders action inputs by {@linkplain #getExecPath() exec paths}, nulls first. */
  @Override
  default int compareTo(ActionInput other) {
    return EXEC_PATH_COMPARATOR.compare(this, other);
  }
}