src/main/java/com/google/devtools/build/lib/exec/SpawnInputExpander.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.exec;

import static com.google.devtools.build.lib.exec.FilesetManifest.RelativeSymlinkBehavior.ERROR;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import com.google.devtools.build.lib.actions.ActionInput;
import com.google.devtools.build.lib.actions.ActionInputFileCache;
import com.google.devtools.build.lib.actions.ActionInputHelper;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.Artifact.ArtifactExpander;
import com.google.devtools.build.lib.actions.RunfilesSupplier;
import com.google.devtools.build.lib.actions.Spawn;
import com.google.devtools.build.lib.actions.cache.VirtualActionInput;
import com.google.devtools.build.lib.actions.cache.VirtualActionInput.EmptyActionInput;
import com.google.devtools.build.lib.rules.fileset.FilesetActionContext;
import com.google.devtools.build.lib.vfs.Path;
import com.google.devtools.build.lib.vfs.PathFragment;
import java.io.IOException;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.SortedMap;
import java.util.TreeMap;

/**
 * A helper class for spawn strategies to turn runfiles suppliers into input mappings. This class
 * performs no I/O operations, but only rearranges the files according to how the runfiles should be
 * laid out.
 */
public class SpawnInputExpander {
  @VisibleForTesting
  static final ActionInput EMPTY_FILE = new EmptyActionInput("/dev/null");

  private final Path execRoot;
  private final boolean strict;

  /**
   * Creates a new instance. If strict is true, then the expander checks for directories in runfiles
   * and throws an exception if it finds any. Otherwise it silently ignores directories in runfiles
   * and adds a mapping for them. At this time, directories in filesets are always silently added as
   * mappings.
   *
   * <p>Directories in inputs are a correctness issue: Bazel only tracks dependencies at the action
   * level, and it does not track dependencies on directories. Making a directory available to a
   * spawn even though it's contents are not tracked as dependencies leads to incorrect incremental
   * builds, since changes to the contents do not trigger action invalidation.
   *
   * <p>As such, all spawn strategies should always be strict and not make directories available to
   * the subprocess. However, that's a breaking change, and therefore we make it depend on this flag
   * for now.
   */
  public SpawnInputExpander(Path execRoot, boolean strict) {
    this.execRoot = execRoot;
    this.strict = strict;
  }

  private void addMapping(
      Map<PathFragment, ActionInput> inputMappings,
      PathFragment targetLocation,
      ActionInput input) {
    Preconditions.checkArgument(!targetLocation.isAbsolute(), targetLocation);
    if (!inputMappings.containsKey(targetLocation)) {
      inputMappings.put(targetLocation, input);
    }
  }

  /** Adds runfiles inputs from runfilesSupplier to inputMappings. */
  @VisibleForTesting
  void addRunfilesToInputs(
      Map<PathFragment, ActionInput> inputMap,
      RunfilesSupplier runfilesSupplier,
      ActionInputFileCache actionFileCache) throws IOException {
    Map<PathFragment, Map<PathFragment, Artifact>> rootsAndMappings = null;
    rootsAndMappings = runfilesSupplier.getMappings();

    for (Entry<PathFragment, Map<PathFragment, Artifact>> rootAndMappings :
        rootsAndMappings.entrySet()) {
      PathFragment root = rootAndMappings.getKey();
      Preconditions.checkState(!root.isAbsolute(), root);
      for (Entry<PathFragment, Artifact> mapping : rootAndMappings.getValue().entrySet()) {
        PathFragment location = root.getRelative(mapping.getKey());
        Artifact localArtifact = mapping.getValue();
        if (localArtifact != null) {
          if (strict && !actionFileCache.getMetadata(localArtifact).getType().isFile()) {
            throw new IOException("Not a file: " + localArtifact.getPath().getPathString());
          }
          addMapping(inputMap, location, localArtifact);
        } else {
          addMapping(inputMap, location, EMPTY_FILE);
        }
      }
    }
  }

  /**
   * Parses the fileset manifest file, adding to the inputMappings where appropriate. Lines
   * referring to directories are recursed.
   */
  @VisibleForTesting
  void parseFilesetManifest(
      Map<PathFragment, ActionInput> inputMappings, Artifact manifest, String workspaceName)
      throws IOException {
    FilesetManifest filesetManifest =
        FilesetManifest.parseManifestFile(manifest, execRoot, workspaceName, ERROR);
    for (Map.Entry<PathFragment, String> mapping : filesetManifest.getEntries().entrySet()) {
      String value = mapping.getValue();
      ActionInput artifact = value == null ? EMPTY_FILE : ActionInputHelper.fromPath(value);
      addMapping(inputMappings, mapping.getKey(), artifact);
    }
  }

  private void addInputs(
      Map<PathFragment, ActionInput> inputMap, Spawn spawn, ArtifactExpander artifactExpander) {
    List<ActionInput> inputs =
        ActionInputHelper.expandArtifacts(spawn.getInputFiles(), artifactExpander);
    for (ActionInput input : inputs) {
      addMapping(inputMap, input.getExecPath(), input);
    }
  }

  /**
   * Convert the inputs of the given spawn to a map from exec-root relative paths to action inputs.
   * The returned map never contains {@code null} values; it uses {@link #EMPTY_FILE} for empty
   * files, which is an instance of {@link VirtualActionInput}.
   */
  public SortedMap<PathFragment, ActionInput> getInputMapping(
      Spawn spawn, ArtifactExpander artifactExpander, ActionInputFileCache actionInputFileCache,
      FilesetActionContext filesetContext)
          throws IOException {
    return getInputMapping(
        spawn,
        artifactExpander,
        actionInputFileCache,
        filesetContext == null ? null : filesetContext.getWorkspaceName());
  }

  /**
   * Convert the inputs of the given spawn to a map from exec-root relative paths to action inputs.
   * In some cases, this generates empty files, for which it uses {@code null}.
   */
  public SortedMap<PathFragment, ActionInput> getInputMapping(
      Spawn spawn, ArtifactExpander artifactExpander, ActionInputFileCache actionInputFileCache,
      String workspaceName)
          throws IOException {
    TreeMap<PathFragment, ActionInput> inputMap = new TreeMap<>();
    addInputs(inputMap, spawn, artifactExpander);
    addRunfilesToInputs(
        inputMap, spawn.getRunfilesSupplier(), actionInputFileCache);
    for (Artifact manifest : spawn.getFilesetManifests()) {
      parseFilesetManifest(inputMap, manifest, workspaceName);
    }
    return inputMap;
  }
}