Automated rollback of commit 39974a43abdd32e3a1acbc7da945b08da9983e4e.

*** Reason for rollback ***

b/112458627

*** Original change description ***

Allow skyframe-aware actions to pass partial results through ActionExecutionContext.
Remove FilesetProvider.

PiperOrigin-RevId: 208213955

25 files changed, 504 insertions, 192 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/actions/ActionExecutionContext.java b/src/main/java/com/google/devtools/build/lib/actions/ActionExecutionContext.java
index 44a79f9314..037f47b1ad 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/ActionExecutionContext.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/ActionExecutionContext.java
@@ -69,7 +69,6 @@ public class ActionExecutionContext implements Closeable {
   @Nullable private final Environment env;
 
   @Nullable private final FileSystem actionFileSystem;
-  @Nullable private final Object skyframeDepsResult;
 
   @Nullable private ImmutableList<FilesetOutputSymlink> outputSymlinks;
 
@@ -86,8 +85,7 @@ public class ActionExecutionContext implements Closeable {
       ImmutableMap<PathFragment, ImmutableList<FilesetOutputSymlink>> inputFilesetMappings,
       @Nullable ArtifactExpander artifactExpander,
       @Nullable SkyFunction.Environment env,
-      @Nullable FileSystem actionFileSystem,
-      @Nullable Object skyframeDepsResult) {
+      @Nullable FileSystem actionFileSystem) {
     this.actionInputFileCache = actionInputFileCache;
     this.actionInputPrefetcher = actionInputPrefetcher;
     this.actionKeyContext = actionKeyContext;
@@ -99,7 +97,6 @@ public class ActionExecutionContext implements Closeable {
     this.artifactExpander = artifactExpander;
     this.env = env;
     this.actionFileSystem = actionFileSystem;
-    this.skyframeDepsResult = skyframeDepsResult;
     this.pathResolver = ArtifactPathResolver.createPathResolver(actionFileSystem,
         // executor is only ever null in testing.
         executor == null ? null : executor.getExecRoot());
@@ -115,8 +112,7 @@ public class ActionExecutionContext implements Closeable {
       Map<String, String> clientEnv,
       ImmutableMap<PathFragment, ImmutableList<FilesetOutputSymlink>> inputFilesetMappings,
       ArtifactExpander artifactExpander,
-      @Nullable FileSystem actionFileSystem,
-      @Nullable Object skyframeDepsResult) {
+      @Nullable FileSystem actionFileSystem) {
     this(
         executor,
         actionInputFileCache,
@@ -128,8 +124,7 @@ public class ActionExecutionContext implements Closeable {
         inputFilesetMappings,
         artifactExpander,
         /*env=*/ null,
-        actionFileSystem,
-        skyframeDepsResult);
+        actionFileSystem);
   }
 
   public static ActionExecutionContext forInputDiscovery(
@@ -153,8 +148,7 @@ public class ActionExecutionContext implements Closeable {
         ImmutableMap.of(),
         /*artifactExpander=*/ null,
         env,
-        actionFileSystem,
-        /*skyframeDepsResult=*/ null);
+        actionFileSystem);
   }
 
   public ActionInputPrefetcher getActionInputPrefetcher() {
@@ -284,11 +278,6 @@ public class ActionExecutionContext implements Closeable {
     return artifactExpander;
   }
 
-  @Nullable
-  public Object getSkyframeDepsResult() {
-    return skyframeDepsResult;
-  }
-
   /**
    * Provide that {@code FileOutErr} that the action should use for redirecting the output and error
    * stream.
@@ -329,7 +318,6 @@ public class ActionExecutionContext implements Closeable {
         inputFilesetMappings,
         artifactExpander,
         env,
-        actionFileSystem,
-        skyframeDepsResult);
+        actionFileSystem);
   }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParams.java b/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParams.java
index e7cbe12c2c..75907d4f24 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParams.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParams.java
@@ -16,6 +16,7 @@ package com.google.devtools.build.lib.actions;
 import com.google.auto.value.AutoValue;
 import com.google.auto.value.extension.memoized.Memoized;
 import com.google.common.base.Optional;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSortedSet;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
@@ -279,14 +280,14 @@ public interface FilesetTraversalParams {
   Optional<DirectTraversal> getDirectTraversal();
 
   /**
-   * Returns the Fileset Artifact of the nested traversal request, if any.
+   * Returns the parameters of the nested traversal request, if any.
    *
    * <p>A nested traversal is the traversal of another Fileset referenced by FilesetEntry.srcdir.
    *
-   * <p>The value is null when {@link #getDirectTraversal} is absent.
+   * <p>The value is non-empty when {@link #getDirectTraversal} is absent AND the nested Fileset has
+   * non-empty FilesetEntries.
    */
-  @Nullable
-  Artifact getNestedArtifact();
+  ImmutableList<FilesetTraversalParams> getNestedTraversal();
 
   /** Adds the fingerprint of this traversal object. */
   void fingerprint(Fingerprint fp);
diff --git a/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParamsFactory.java b/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParamsFactory.java
index 6fd7cfa8d5..f9585f34df 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParamsFactory.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParamsFactory.java
@@ -17,7 +17,9 @@ import com.google.auto.value.AutoValue;
 import com.google.auto.value.extension.memoized.Memoized;
 import com.google.common.base.Optional;
 import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSortedSet;
+import com.google.common.collect.Iterables;
 import com.google.common.collect.Ordering;
 import com.google.devtools.build.lib.actions.FilesetTraversalParams.DirectTraversalRoot;
 import com.google.devtools.build.lib.actions.FilesetTraversalParams.PackageBoundaryMode;
@@ -108,11 +110,13 @@ public final class FilesetTraversalParamsFactory {
   }
 
   /**
-   * Creates traversal request parameters for a FilesetEntry wrapping another Fileset.
+   * Creates traversal request parameters for a FilesetEntry wrapping another Fileset. If possible,
+   * the original {@code nested} is returned to avoid unnecessary object creation. In that case, the
+   * {@code ownerLabelForErrorMessages} may be ignored. Since the wrapping traversal could not have
+   * an error on its own, any error messages printed will still be correct.
    *
    * @param ownerLabel the rule that created this object
-   * @param artifact the Fileset Artifact of traversal params that were used for the nested (inner)
-   *     Fileset
+   * @param nested the list of traversal params that were used for the nested (inner) Fileset
    * @param destPath path in the Fileset's output directory that will be the root of files coming
    *     from the nested Fileset
    * @param excludes optional; set of files directly below (not in a subdirectory of) the nested
@@ -120,11 +124,16 @@ public final class FilesetTraversalParamsFactory {
    */
   public static FilesetTraversalParams nestedTraversal(
       Label ownerLabel,
-      Artifact artifact,
+      ImmutableList<FilesetTraversalParams> nested,
       PathFragment destPath,
       @Nullable Set<String> excludes) {
+    if (nested.size() == 1 && destPath.isEmpty() && (excludes == null || excludes.isEmpty())) {
+      // Wrapping the traversal here would not lead to a different result: the output location is
+      // the same and there are no additional excludes.
+      return Iterables.getOnlyElement(nested);
+    }
     // When srcdir is another Fileset, then files must be null so strip_prefix must also be null.
-    return NestedTraversalParams.getNestedTraversal(ownerLabel, artifact, destPath, excludes);
+    return NestedTraversalParams.getNestedTraversal(ownerLabel, nested, destPath, excludes);
   }
 
   private static ImmutableSortedSet<String> getOrderedExcludes(@Nullable Set<String> excludes) {
@@ -138,8 +147,8 @@ public final class FilesetTraversalParamsFactory {
   @AutoValue
   abstract static class DirectoryTraversalParams implements FilesetTraversalParams {
     @Override
-    public Artifact getNestedArtifact() {
-      return null;
+    public ImmutableList<FilesetTraversalParams> getNestedTraversal() {
+      return ImmutableList.of();
     }
 
     @Memoized
@@ -209,7 +218,7 @@ public final class FilesetTraversalParamsFactory {
       if (!getExcludedFiles().isEmpty()) {
         fp.addStrings(getExcludedFiles());
       }
-      fp.addPath(getNestedArtifact().getExecPath());
+      getNestedTraversal().forEach(nestedTraversal -> nestedTraversal.fingerprint(fp));
       return fp.digestAndReset();
     }
 
@@ -220,10 +229,10 @@ public final class FilesetTraversalParamsFactory {
 
     static NestedTraversalParams getNestedTraversal(
         Label ownerLabel,
-        Artifact nestedArtifact,
+        ImmutableList<FilesetTraversalParams> nested,
         PathFragment destPath,
         @Nullable Set<String> excludes) {
-      return create(ownerLabel, destPath, getOrderedExcludes(excludes), nestedArtifact);
+      return create(ownerLabel, destPath, getOrderedExcludes(excludes), nested);
     }
 
     @AutoCodec.VisibleForSerialization
@@ -232,9 +241,9 @@ public final class FilesetTraversalParamsFactory {
         Label ownerLabelForErrorMessages,
         PathFragment destPath,
         ImmutableSortedSet<String> excludedFiles,
-        Artifact nestedArtifact) {
+        ImmutableList<FilesetTraversalParams> nestedTraversal) {
       return new AutoValue_FilesetTraversalParamsFactory_NestedTraversalParams(
-          ownerLabelForErrorMessages, destPath, excludedFiles, nestedArtifact);
+          ownerLabelForErrorMessages, destPath, excludedFiles, nestedTraversal);
     }
   }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTargetFactory.java b/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTargetFactory.java
index dbce56b589..30861cd3ac 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTargetFactory.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTargetFactory.java
@@ -31,9 +31,11 @@ import com.google.devtools.build.lib.analysis.config.BuildConfiguration.Fragment
 import com.google.devtools.build.lib.analysis.config.BuildOptions;
 import com.google.devtools.build.lib.analysis.config.ConfigMatchingProvider;
 import com.google.devtools.build.lib.analysis.configuredtargets.EnvironmentGroupConfiguredTarget;
+import com.google.devtools.build.lib.analysis.configuredtargets.FilesetOutputConfiguredTarget;
 import com.google.devtools.build.lib.analysis.configuredtargets.InputFileConfiguredTarget;
 import com.google.devtools.build.lib.analysis.configuredtargets.OutputFileConfiguredTarget;
 import com.google.devtools.build.lib.analysis.configuredtargets.PackageGroupConfiguredTarget;
+import com.google.devtools.build.lib.analysis.fileset.FilesetProvider;
 import com.google.devtools.build.lib.analysis.skylark.SkylarkRuleConfiguredTargetUtil;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.collect.nestedset.NestedSet;
@@ -230,7 +232,16 @@ public final class ConfiguredTargetFactory {
       }
       TransitiveInfoCollection rule = targetContext.findDirectPrerequisite(
           outputFile.getGeneratingRule().getLabel(), config);
+      if (isFileset) {
+        return new FilesetOutputConfiguredTarget(
+            targetContext,
+            outputFile,
+            rule,
+            artifact,
+            rule.getProvider(FilesetProvider.class).getTraversals());
+      } else {
         return new OutputFileConfiguredTarget(targetContext, outputFile, rule, artifact);
+      }
     } else if (target instanceof InputFile) {
       InputFile inputFile = (InputFile) target;
       SourceArtifact artifact =
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java b/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
index 0cccfb8345..3eebb2d037 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
@@ -55,6 +55,7 @@ import com.google.devtools.build.lib.analysis.config.transitions.PatchTransition
 import com.google.devtools.build.lib.analysis.config.transitions.SplitTransition;
 import com.google.devtools.build.lib.analysis.configuredtargets.RuleConfiguredTarget.Mode;
 import com.google.devtools.build.lib.analysis.constraints.ConstraintSemantics;
+import com.google.devtools.build.lib.analysis.fileset.FilesetProvider;
 import com.google.devtools.build.lib.analysis.platform.PlatformInfo;
 import com.google.devtools.build.lib.analysis.stringtemplate.TemplateContext;
 import com.google.devtools.build.lib.cmdline.Label;
@@ -1554,12 +1555,9 @@ public final class RuleContext extends TargetContext
     }
 
     private boolean validateFilesetEntry(FilesetEntry filesetEntry, ConfiguredTargetAndData src) {
-      NestedSet<Artifact> filesToBuild =
-          src.getConfiguredTarget().getProvider(FileProvider.class).getFilesToBuild();
-      if (filesToBuild.isSingleton() && Iterables.getOnlyElement(filesToBuild).isFileset()) {
+      if (src.getConfiguredTarget().getProvider(FilesetProvider.class) != null) {
         return true;
       }
-
       if (filesetEntry.isSourceFileset()) {
         return true;
       }
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/configuredtargets/FileConfiguredTarget.java b/src/main/java/com/google/devtools/build/lib/analysis/configuredtargets/FileConfiguredTarget.java
index cd959fa858..2fec10f91e 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/configuredtargets/FileConfiguredTarget.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/configuredtargets/FileConfiguredTarget.java
@@ -23,6 +23,7 @@ import com.google.devtools.build.lib.analysis.TransitiveInfoProvider;
 import com.google.devtools.build.lib.analysis.TransitiveInfoProviderMap;
 import com.google.devtools.build.lib.analysis.TransitiveInfoProviderMapBuilder;
 import com.google.devtools.build.lib.analysis.VisibilityProvider;
+import com.google.devtools.build.lib.analysis.fileset.FilesetProvider;
 import com.google.devtools.build.lib.analysis.test.InstrumentedFilesProvider;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.collect.nestedset.NestedSet;
@@ -61,6 +62,9 @@ public abstract class FileConfiguredTarget extends AbstractConfiguredTarget
             .put(LicensesProvider.class, this)
             .add(fileProvider)
             .add(filesToRunProvider);
+    if (this instanceof FilesetProvider) {
+      builder.put(FilesetProvider.class, this);
+    }
     if (this instanceof InstrumentedFilesProvider) {
       builder.put(InstrumentedFilesProvider.class, this);
     }
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/configuredtargets/FilesetOutputConfiguredTarget.java b/src/main/java/com/google/devtools/build/lib/analysis/configuredtargets/FilesetOutputConfiguredTarget.java
new file mode 100644
index 0000000000..08dc1ac78e
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/analysis/configuredtargets/FilesetOutputConfiguredTarget.java
@@ -0,0 +1,84 @@
+// 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.analysis.configuredtargets;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableList;
+import com.google.devtools.build.lib.actions.Artifact;
+import com.google.devtools.build.lib.actions.FilesetTraversalParams;
+import com.google.devtools.build.lib.analysis.TargetContext;
+import com.google.devtools.build.lib.analysis.TransitiveInfoCollection;
+import com.google.devtools.build.lib.analysis.fileset.FilesetProvider;
+import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.collect.nestedset.NestedSet;
+import com.google.devtools.build.lib.packages.OutputFile;
+import com.google.devtools.build.lib.packages.PackageSpecification.PackageGroupContents;
+import com.google.devtools.build.lib.skyframe.BuildConfigurationValue;
+import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
+
+/**
+ * A configured target for output files generated by {@code Fileset} rules. They are almost the same
+ * thing as output files except that they implement {@link FilesetProvider} so that {@code Fileset}
+ * can figure out the link tree behind them.
+ *
+ * <p>In an ideal world, this would not be needed: Filesets would depend on other Filesets and not
+ * their output directories. However, sometimes a Fileset depends on the output directory of another
+ * Fileset. Thus, we need this hack.
+ */
+@AutoCodec
+public final class FilesetOutputConfiguredTarget extends OutputFileConfiguredTarget
+    implements FilesetProvider {
+  private final ImmutableList<FilesetTraversalParams> filesetTraversals;
+
+  public FilesetOutputConfiguredTarget(
+      TargetContext targetContext,
+      OutputFile outputFile,
+      TransitiveInfoCollection generatingRule,
+      Artifact outputArtifact,
+      ImmutableList<FilesetTraversalParams> traversals) {
+    this(
+        targetContext.getLabel(),
+        targetContext.getConfigurationKey(),
+        targetContext.getVisibility(),
+        generatingRule,
+        outputArtifact,
+        traversals);
+    Preconditions.checkState(
+        outputFile.getLabel().equals(targetContext.getLabel()),
+        "mismatch: %s %s",
+        outputFile,
+        targetContext);
+  }
+
+  @AutoCodec.VisibleForSerialization
+  @AutoCodec.Instantiator
+  FilesetOutputConfiguredTarget(
+      Label label,
+      BuildConfigurationValue.Key configurationKey,
+      NestedSet<PackageGroupContents> visibility,
+      TransitiveInfoCollection generatingRule,
+      Artifact artifact,
+      ImmutableList<FilesetTraversalParams> traversals) {
+    super(label, configurationKey, visibility, artifact, generatingRule);
+    FilesetProvider provider = generatingRule.getProvider(FilesetProvider.class);
+    Preconditions.checkArgument(provider != null);
+    filesetTraversals = traversals;
+  }
+
+  @Override
+  public ImmutableList<FilesetTraversalParams> getTraversals() {
+    return filesetTraversals;
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/fileset/FilesetProvider.java b/src/main/java/com/google/devtools/build/lib/analysis/fileset/FilesetProvider.java
new file mode 100644
index 0000000000..225a40eb42
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/analysis/fileset/FilesetProvider.java
@@ -0,0 +1,30 @@
+// 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.analysis.fileset;
+
+import com.google.common.collect.ImmutableList;
+import com.google.devtools.build.lib.actions.FilesetTraversalParams;
+import com.google.devtools.build.lib.analysis.TransitiveInfoProvider;
+
+/**
+ * Information needed by a Fileset to do the right thing when it depends on another Fileset.
+ */
+public interface FilesetProvider extends TransitiveInfoProvider {
+  /**
+   * Returns a list of the traversals that went into this Fileset. Only used by Skyframe-native
+   * filesets, so will be null if Skyframe-native filesets are not enabled.
+   */
+  ImmutableList<FilesetTraversalParams> getTraversals();
+}
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ActionExecutionFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/ActionExecutionFunction.java
index 0905cf1bef..7bff8b0193 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ActionExecutionFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ActionExecutionFunction.java
@@ -187,9 +187,8 @@ public class ActionExecutionFunction implements SkyFunction, CompletionReceiver
       return null;
     }
 
-    Object skyframeDepsResult;
     try {
-      skyframeDepsResult = establishSkyframeDependencies(env, action);
+      establishSkyframeDependencies(env, action);
     } catch (ActionExecutionException e) {
       throw new ActionExecutionFunctionException(e);
     }
@@ -214,8 +213,7 @@ public class ActionExecutionFunction implements SkyFunction, CompletionReceiver
     try {
       result =
           checkCacheAndExecuteIfNeeded(
-              action, state, env, clientEnv, actionLookupData, sharedActionAlreadyRan,
-              skyframeDepsResult);
+              action, state, env, clientEnv, actionLookupData, sharedActionAlreadyRan);
     } catch (ActionExecutionException e) {
       // Remove action from state map in case it's there (won't be unless it discovers inputs).
       stateMap.remove(action);
@@ -365,8 +363,7 @@ public class ActionExecutionFunction implements SkyFunction, CompletionReceiver
       Environment env,
       Map<String, String> clientEnv,
       ActionLookupData actionLookupData,
-      boolean sharedActionAlreadyRan,
-      Object skyframeDepsResult)
+      boolean sharedActionAlreadyRan)
       throws ActionExecutionException, InterruptedException {
     // If this is a shared action and the other action is the one that executed, we must use that
     // other action's value, provided here, since it is populated with metadata for the outputs.
@@ -499,8 +496,7 @@ public class ActionExecutionFunction implements SkyFunction, CompletionReceiver
             metadataHandler,
             Collections.unmodifiableMap(state.expandedArtifacts),
             filesets,
-            state.actionFileSystem,
-            skyframeDepsResult)) {
+            state.actionFileSystem)) {
       if (!state.hasExecutedAction()) {
         state.value =
             skyframeActionExecutor.executeAction(
@@ -601,7 +597,7 @@ public class ActionExecutionFunction implements SkyFunction, CompletionReceiver
     }
   }
 
-  private static Object establishSkyframeDependencies(Environment env, Action action)
+  private static void establishSkyframeDependencies(Environment env, Action action)
       throws ActionExecutionException, InterruptedException {
     // Before we may safely establish Skyframe dependencies, we must build all action inputs by
     // requesting their ArtifactValues.
@@ -618,12 +614,11 @@ public class ActionExecutionFunction implements SkyFunction, CompletionReceiver
       Preconditions.checkState(action.executeUnconditionally(), action);
 
       try {
-        return ((SkyframeAwareAction) action).establishSkyframeDependencies(env);
+        ((SkyframeAwareAction) action).establishSkyframeDependencies(env);
       } catch (SkyframeAwareAction.ExceptionBase e) {
         throw new ActionExecutionException(e, action, false);
       }
     }
-    return null;
   }
 
   private static Iterable<SkyKey> toKeys(
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunction.java
index aa155b1cb3..22f5b31935 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunction.java
@@ -51,129 +51,151 @@ public final class FilesetEntryFunction implements SkyFunction {
   public SkyValue compute(SkyKey key, Environment env)
       throws FilesetEntryFunctionException, InterruptedException {
     FilesetTraversalParams t = (FilesetTraversalParams) key.argument();
-    Preconditions.checkState(
-        t.getDirectTraversal().isPresent() && t.getNestedArtifact() == null,
-        "FilesetEntry does not support nested traversal: %s", t);
+    if (t.getDirectTraversal().isPresent()) {
+      Preconditions.checkState(
+          t.getNestedTraversal().isEmpty(),
+          "NestedTraversal must be empty if directTraversal is present: %s", t);
+    }
+
+    // Create the set of excluded files. Only top-level files can be excluded, i.e. ones that are
+    // directly under the root if the root is a directory.
+    Set<String> exclusions =
+        Sets.filter(t.getExcludedFiles(), e -> PathFragment.create(e).segmentCount() == 1);
 
     // The map of output symlinks. Each key is the path of a output symlink that the Fileset must
     // create, relative to the Fileset.out directory, and each value specifies extra information
     // about the link (its target, associated metadata and again its name).
     Map<PathFragment, FilesetOutputSymlink> outputSymlinks = new LinkedHashMap<>();
 
-    // The "direct" traversal params are present, which is the case when the FilesetEntry
-    // specifies a package's BUILD file, a directory or a list of files.
-
-    // The root of the direct traversal is defined as follows.
-    //
-    // If FilesetEntry.files is specified, then a TraversalRequest is created for each entry, the
-    // root being the respective entry itself. These are all traversed for they may be
-    // directories or symlinks to directories, and we need to establish Skyframe dependencies on
-    // their contents for incremental correctness. If an entry is indeed a directory (but not when
-    // it's a symlink to one) then we have to create symlinks to each of their childen.
-    // (NB: there seems to be no good reason for this, it's just how legacy Fileset works. We may
-    // want to consider creating a symlink just for the directory and not for its child elements.)
-    //
-    // If FilesetEntry.files is not specified, then srcdir refers to either a BUILD file or a
-    // directory. For the former, the root will be the parent of the BUILD file. For the latter,
-    // the root will be srcdir itself.
-    DirectTraversal direct = t.getDirectTraversal().get();
-
-    RecursiveFilesystemTraversalValue rftv;
-    try {
-      // Traverse the filesystem to establish skyframe dependencies.
-      rftv = traverse(env, createErrorInfo(t), direct);
-    } catch (MissingDepException e) {
-      return null;
-    }
-
-    // The root can only be absent for the EMPTY rftv instance.
-    if (!rftv.getResolvedRoot().isPresent()) {
-      return FilesetEntryValue.EMPTY;
-    }
-
-    ResolvedFile resolvedRoot = rftv.getResolvedRoot().get();
-
-    // Handle dangling symlinks gracefully be returning empty results.
-    if (!resolvedRoot.getType().exists()) {
-      return FilesetEntryValue.EMPTY;
-    }
+    if (!t.getDirectTraversal().isPresent()) {
+      // The absence of "direct" traversal indicates the presence of a "nested" fileset and
+      // getNestedTraversal will return the list FilesetTraversalParams corresponding to each
+      // FilesetEntry of the nested Fileset.
+      ImmutableList<SkyKey> nestedKeys = FilesetEntryKey.keys(t.getNestedTraversal());
+      Map<SkyKey, SkyValue> results = env.getValues(nestedKeys);
+      if (env.valuesMissing()) {
+        return null;
+      }
 
-    // The prefix to remove is the entire path of the root. This is OK:
-    // - when the root is a file, this removes the entire path, but the traversal's destination
-    //   path is actually the name of the output symlink, so this works out correctly
-    // - when the root is a directory or a symlink to one then we need to strip off the
-    //   directory's path from every result (this is how the output symlinks must be created)
-    //   before making them relative to the destination path
-    PathFragment prefixToRemove = direct.getRoot().getRelativePart();
-
-    Iterable<ResolvedFile> results = null;
-
-    if (direct.isRecursive()
-        || (resolvedRoot.getType().isDirectory() && !resolvedRoot.getType().isSymlink())) {
-      // The traversal is recursive (requested for an entire FilesetEntry.srcdir) or it was
-      // requested for a FilesetEntry.files entry which turned out to be a directory. We need to
-      // create an output symlink for every file in it and all of its subdirectories. Only
-      // exception is when the subdirectory is really a symlink to a directory -- no output
-      // shall be created for the contents of those.
-      // Now we create Dir objects to model the filesystem tree. The object employs a trick to
-      // find directory symlinks: directory symlinks have corresponding ResolvedFile entries and
-      // are added as files too, while their children, also added as files, contain the path of
-      // the parent. Finding and discarding the children is easy if we traverse the tree from
-      // root to leaf.
-      DirectoryTree root = new DirectoryTree();
-      for (ResolvedFile f : rftv.getTransitiveFiles().toCollection()) {
-        PathFragment path = f.getNameInSymlinkTree().relativeTo(prefixToRemove);
-        if (!path.isEmpty()) {
-          path = t.getDestPath().getRelative(path);
-          DirectoryTree dir = root;
-          for (int i = 0; i < path.segmentCount() - 1; ++i) {
-            dir = dir.addOrGetSubdir(path.getSegment(i));
+      for (SkyKey nestedKey : nestedKeys) {
+        FilesetEntryValue nested = (FilesetEntryValue) results.get(nestedKey);
+        for (FilesetOutputSymlink s : nested.getSymlinks()) {
+          if (!exclusions.contains(s.getName().getPathString())) {
+            maybeStoreSymlink(s, t.getDestPath(), outputSymlinks);
           }
-          dir.maybeAddFile(f);
         }
       }
-      // Here's where the magic happens. The returned iterable will yield all files in the
-      // directory that are not under symlinked directories, as well as all directory symlinks.
-      results = root.iterateFiles();
     } else {
-      // If we're on this branch then the traversal was done for just one entry in
-      // FilesetEntry.files (which was not a directory, so it was either a file, a symlink to one
-      // or a symlink to a directory), meaning we'll have only one output symlink.
-      results = ImmutableList.of(resolvedRoot);
-    }
+      // The "direct" traversal params are present, which is the case when the FilesetEntry
+      // specifies a package's BUILD file, a directory or a list of files.
+
+      // The root of the direct traversal is defined as follows.
+      //
+      // If FilesetEntry.files is specified, then a TraversalRequest is created for each entry, the
+      // root being the respective entry itself. These are all traversed for they may be
+      // directories or symlinks to directories, and we need to establish Skyframe dependencies on
+      // their contents for incremental correctness. If an entry is indeed a directory (but not when
+      // it's a symlink to one) then we have to create symlinks to each of their childen.
+      // (NB: there seems to be no good reason for this, it's just how legacy Fileset works. We may
+      // want to consider creating a symlink just for the directory and not for its child elements.)
+      //
+      // If FilesetEntry.files is not specified, then srcdir refers to either a BUILD file or a
+      // directory. For the former, the root will be the parent of the BUILD file. For the latter,
+      // the root will be srcdir itself.
+      DirectTraversal direct = t.getDirectTraversal().get();
 
-    // Create the set of excluded files. Only top-level files can be excluded, i.e. ones that are
-    // directly under the root if the root is a directory.
-    Set<String> exclusions =
-        Sets.filter(t.getExcludedFiles(), e -> PathFragment.create(e).segmentCount() == 1);
+      RecursiveFilesystemTraversalValue rftv;
+      try {
+        // Traverse the filesystem to establish skyframe dependencies.
+        rftv = traverse(env, createErrorInfo(t), direct);
+      } catch (MissingDepException e) {
+        return null;
+      }
 
-    // Create one output symlink for each entry in the results.
-    for (ResolvedFile f : results) {
-      // The linkName has to be under the traversal's root, which is also the prefix to remove.
-      PathFragment linkName = f.getNameInSymlinkTree().relativeTo(prefixToRemove);
-
-      // Check whether the symlink is excluded before attempting to resolve it.
-      // It may be dangling, but excluding it is still fine.
-      // TODO(b/64754128): Investigate if we could have made the exclude earlier before
-      //                   unnecessarily iterating over all the files in an excluded directory.
-      if (linkName.segmentCount() > 0 && exclusions.contains(linkName.getSegment(0))) {
-        continue;
+      // The root can only be absent for the EMPTY rftv instance.
+      if (!rftv.getResolvedRoot().isPresent()) {
+        return FilesetEntryValue.EMPTY;
       }
 
-      PathFragment targetName;
-      try {
-        targetName = f.getTargetInSymlinkTree(direct.isFollowingSymlinks());
-      } catch (DanglingSymlinkException e) {
-        throw new FilesetEntryFunctionException(e);
+      ResolvedFile resolvedRoot = rftv.getResolvedRoot().get();
+
+      // Handle dangling symlinks gracefully be returning empty results.
+      if (!resolvedRoot.getType().exists()) {
+        return FilesetEntryValue.EMPTY;
+      }
+
+      // The prefix to remove is the entire path of the root. This is OK:
+      // - when the root is a file, this removes the entire path, but the traversal's destination
+      //   path is actually the name of the output symlink, so this works out correctly
+      // - when the root is a directory or a symlink to one then we need to strip off the
+      //   directory's path from every result (this is how the output symlinks must be created)
+      //   before making them relative to the destination path
+      PathFragment prefixToRemove = direct.getRoot().getRelativePart();
+
+      Iterable<ResolvedFile> results = null;
+
+      if (direct.isRecursive()
+          || (resolvedRoot.getType().isDirectory() && !resolvedRoot.getType().isSymlink())) {
+        // The traversal is recursive (requested for an entire FilesetEntry.srcdir) or it was
+        // requested for a FilesetEntry.files entry which turned out to be a directory. We need to
+        // create an output symlink for every file in it and all of its subdirectories. Only
+        // exception is when the subdirectory is really a symlink to a directory -- no output
+        // shall be created for the contents of those.
+        // Now we create Dir objects to model the filesystem tree. The object employs a trick to
+        // find directory symlinks: directory symlinks have corresponding ResolvedFile entries and
+        // are added as files too, while their children, also added as files, contain the path of
+        // the parent. Finding and discarding the children is easy if we traverse the tree from
+        // root to leaf.
+        DirectoryTree root = new DirectoryTree();
+        for (ResolvedFile f : rftv.getTransitiveFiles().toCollection()) {
+          PathFragment path = f.getNameInSymlinkTree().relativeTo(prefixToRemove);
+          if (!path.isEmpty()) {
+            path = t.getDestPath().getRelative(path);
+            DirectoryTree dir = root;
+            for (int i = 0; i < path.segmentCount() - 1; ++i) {
+              dir = dir.addOrGetSubdir(path.getSegment(i));
+            }
+            dir.maybeAddFile(f);
+          }
+        }
+        // Here's where the magic happens. The returned iterable will yield all files in the
+        // directory that are not under symlinked directories, as well as all directory symlinks.
+        results = root.iterateFiles();
+      } else {
+        // If we're on this branch then the traversal was done for just one entry in
+        // FilesetEntry.files (which was not a directory, so it was either a file, a symlink to one
+        // or a symlink to a directory), meaning we'll have only one output symlink.
+        results = ImmutableList.of(resolvedRoot);
       }
 
-      maybeStoreSymlink(
-          linkName,
-          targetName,
-          f.getMetadata(),
-          t.getDestPath(),
-          direct.isGenerated(),
-          outputSymlinks);
+      // Create one output symlink for each entry in the results.
+      for (ResolvedFile f : results) {
+        // The linkName has to be under the traversal's root, which is also the prefix to remove.
+        PathFragment linkName = f.getNameInSymlinkTree().relativeTo(prefixToRemove);
+
+        // Check whether the symlink is excluded before attempting to resolve it.
+        // It may be dangling, but excluding it is still fine.
+        // TODO(b/64754128): Investigate if we could have made the exclude earlier before
+        //                   unnecessarily iterating over all the files in an excluded directory.
+        if (linkName.segmentCount() > 0 && exclusions.contains(linkName.getSegment(0))) {
+          continue;
+        }
+
+        PathFragment targetName;
+        try {
+          targetName = f.getTargetInSymlinkTree(direct.isFollowingSymlinks());
+        } catch (DanglingSymlinkException e) {
+          throw new FilesetEntryFunctionException(e);
+        }
+
+        maybeStoreSymlink(
+            linkName,
+            targetName,
+            f.getMetadata(),
+            t.getDestPath(),
+            direct.isGenerated(),
+            outputSymlinks);
+      }
     }
 
     return FilesetEntryValue.of(ImmutableSet.copyOf(outputSymlinks.values()));
@@ -181,6 +203,20 @@ public final class FilesetEntryFunction implements SkyFunction {
 
   /** Stores an output symlink unless it would overwrite an existing one. */
   private static void maybeStoreSymlink(
+      FilesetOutputSymlink nestedLink,
+      PathFragment destPath,
+      Map<PathFragment, FilesetOutputSymlink> result) {
+    maybeStoreSymlink(
+        nestedLink.getName(),
+        nestedLink.getTargetPath(),
+        nestedLink.getMetadata(),
+        destPath,
+        nestedLink.isGeneratedTarget(),
+        result);
+  }
+
+  /** Stores an output symlink unless it would overwrite an existing one. */
+  private static void maybeStoreSymlink(
       PathFragment linkName,
       PathFragment linkTarget,
       Object metadata,
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeActionExecutor.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeActionExecutor.java
index 32c0472b1e..5ddabcce58 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeActionExecutor.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeActionExecutor.java
@@ -520,8 +520,7 @@ public final class SkyframeActionExecutor {
       MetadataHandler metadataHandler,
       Map<Artifact, Collection<Artifact>> expandedInputs,
       ImmutableMap<PathFragment, ImmutableList<FilesetOutputSymlink>> inputFilesetMappings,
-      @Nullable FileSystem actionFileSystem,
-      @Nullable Object skyframeDepsResult) {
+      @Nullable FileSystem actionFileSystem) {
     FileOutErr fileOutErr = actionLogBufferPathGenerator.generate(
         ArtifactPathResolver.createPathResolver(actionFileSystem, executorEngine.getExecRoot()));
     return new ActionExecutionContext(
@@ -534,8 +533,7 @@ public final class SkyframeActionExecutor {
         clientEnv,
         inputFilesetMappings,
         new ArtifactExpanderImpl(expandedInputs),
-        actionFileSystem,
-        skyframeDepsResult);
+        actionFileSystem);
   }
 
   /**
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeAwareAction.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeAwareAction.java
index da81769f7a..c351cda50b 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeAwareAction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeAwareAction.java
@@ -68,9 +68,6 @@ public interface SkyframeAwareAction {
    * <p>This method should not attempt to handle errors or missing dependencies (other than wrapping
    * exceptions); that is the responsibility of the caller. It should return as soon as possible,
    * ready to be called again at a later time if need be.
-   *
-   * <p>The return value will be incorporated into the
-   * {@link com.google.devtools.build.lib.actions.ActionExecutionContext}.
    */
-  Object establishSkyframeDependencies(Environment env) throws ExceptionBase, InterruptedException;
+  void establishSkyframeDependencies(Environment env) throws ExceptionBase, InterruptedException;
 }
diff --git a/src/test/java/com/google/devtools/build/lib/actions/ExecutableSymlinkActionTest.java b/src/test/java/com/google/devtools/build/lib/actions/ExecutableSymlinkActionTest.java
index 5f8bf79f1c..9f233b3dd4 100644
--- a/src/test/java/com/google/devtools/build/lib/actions/ExecutableSymlinkActionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/actions/ExecutableSymlinkActionTest.java
@@ -66,7 +66,6 @@ public class ExecutableSymlinkActionTest {
         ImmutableMap.<String, String>of(),
         ImmutableMap.of(),
         null,
-        null,
         null);
   }
 
diff --git a/src/test/java/com/google/devtools/build/lib/actions/util/ActionsTestUtil.java b/src/test/java/com/google/devtools/build/lib/actions/util/ActionsTestUtil.java
index 1aa4022b34..80b8e7e403 100644
--- a/src/test/java/com/google/devtools/build/lib/actions/util/ActionsTestUtil.java
+++ b/src/test/java/com/google/devtools/build/lib/actions/util/ActionsTestUtil.java
@@ -147,8 +147,7 @@ public final class ActionsTestUtil {
         actionGraph == null
             ? createDummyArtifactExpander()
             : ActionInputHelper.actionGraphArtifactExpander(actionGraph),
-        /*actionFileSystem=*/ null,
-        /*skyframeDepsResult=*/ null);
+        /*actionFileSystem=*/ null);
   }
 
   public static ActionExecutionContext createContextForInputDiscovery(
@@ -183,8 +182,7 @@ public final class ActionsTestUtil {
         ImmutableMap.of(),
         ImmutableMap.of(),
         createDummyArtifactExpander(),
-        /*actionFileSystem=*/ null,
-        /*skyframeDepsResult=*/ null);
+        /*actionFileSystem=*/ null);
   }
 
   private static ArtifactExpander createDummyArtifactExpander() {
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/actions/FileWriteActionTestCase.java b/src/test/java/com/google/devtools/build/lib/analysis/actions/FileWriteActionTestCase.java
index fe4b0a2805..12cbfb4ffe 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/actions/FileWriteActionTestCase.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/actions/FileWriteActionTestCase.java
@@ -68,7 +68,6 @@ public abstract class FileWriteActionTestCase extends BuildViewTestCase {
             ImmutableMap.<String, String>of(),
             ImmutableMap.of(),
             null,
-            null,
             null);
   }
 
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/actions/ParamFileWriteActionTest.java b/src/test/java/com/google/devtools/build/lib/analysis/actions/ParamFileWriteActionTest.java
index b736576d57..59364a3328 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/actions/ParamFileWriteActionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/actions/ParamFileWriteActionTest.java
@@ -203,8 +203,7 @@ public class ParamFileWriteActionTest extends BuildViewTestCase {
         ImmutableMap.<String, String>of(),
         ImmutableMap.of(),
         artifactExpander,
-        /*actionFileSystem=*/ null,
-        /*skyframeDepsResult=*/ null);
+        /*actionFileSystem=*/ null);
   }
 
   private enum KeyAttributes {
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/actions/SymlinkActionTest.java b/src/test/java/com/google/devtools/build/lib/analysis/actions/SymlinkActionTest.java
index ae213a4616..c3e25614fd 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/actions/SymlinkActionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/actions/SymlinkActionTest.java
@@ -90,8 +90,7 @@ public class SymlinkActionTest extends BuildViewTestCase {
                 ImmutableMap.<String, String>of(),
                 ImmutableMap.of(),
                 null,
-                /*actionFileSystem=*/ null,
-                /*skyframeDepsResult=*/ null));
+                /*actionFileSystem=*/ null));
     assertThat(actionResult.spawnResults()).isEmpty();
     assertThat(output.isSymbolicLink()).isTrue();
     assertThat(output.resolveSymbolicLinks()).isEqualTo(input);
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/actions/TemplateExpansionActionTest.java b/src/test/java/com/google/devtools/build/lib/analysis/actions/TemplateExpansionActionTest.java
index b7fc6c755e..48c169af4d 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/actions/TemplateExpansionActionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/actions/TemplateExpansionActionTest.java
@@ -192,8 +192,7 @@ public class TemplateExpansionActionTest extends FoundationTestCase {
         ImmutableMap.<String, String>of(),
         ImmutableMap.of(),
         null,
-        /*actionFileSystem=*/ null,
-        /*skyframeDepsResult=*/ null);
+        /*actionFileSystem=*/ null);
   }
 
   private void executeTemplateExpansion(String expected) throws Exception {
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/util/BuildViewTestCase.java b/src/test/java/com/google/devtools/build/lib/analysis/util/BuildViewTestCase.java
index 9a1816864f..c3bea4f72c 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/util/BuildViewTestCase.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/util/BuildViewTestCase.java
@@ -2168,8 +2168,7 @@ public abstract class BuildViewTestCase extends FoundationTestCase {
           clientEnv,
           ImmutableMap.of(),
           artifactExpander,
-          /*actionFileSystem=*/ null,
-          /*skyframeDepsResult*/ null);
+          /*actionFileSystem=*/ null);
     }
   }
 }
diff --git a/src/test/java/com/google/devtools/build/lib/rules/cpp/CreateIncSymlinkActionTest.java b/src/test/java/com/google/devtools/build/lib/rules/cpp/CreateIncSymlinkActionTest.java
index e84c832e47..c447f67450 100644
--- a/src/test/java/com/google/devtools/build/lib/rules/cpp/CreateIncSymlinkActionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/rules/cpp/CreateIncSymlinkActionTest.java
@@ -116,8 +116,7 @@ public class CreateIncSymlinkActionTest extends FoundationTestCase {
   private ActionExecutionContext makeDummyContext() {
     DummyExecutor executor = new DummyExecutor(fileSystem, rootDirectory);
     return new ActionExecutionContext(
-        executor, null, null, null, null, null, ImmutableMap.of(), ImmutableMap.of(), null, null,
-        null);
+        executor, null, null, null, null, null, ImmutableMap.of(), ImmutableMap.of(), null, null);
   }
 
   @Test
diff --git a/src/test/java/com/google/devtools/build/lib/rules/cpp/LtoBackendActionTest.java b/src/test/java/com/google/devtools/build/lib/rules/cpp/LtoBackendActionTest.java
index f8881ee628..25c7e0d444 100644
--- a/src/test/java/com/google/devtools/build/lib/rules/cpp/LtoBackendActionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/rules/cpp/LtoBackendActionTest.java
@@ -90,8 +90,7 @@ public class LtoBackendActionTest extends BuildViewTestCase {
             ImmutableMap.<String, String>of(),
             ImmutableMap.of(),
             null,
-            /*actionFileSystem=*/ null,
-            /*skyframeDepsResult=*/ null);
+            /*actionFileSystem=*/ null);
   }
 
   @Test
diff --git a/src/test/java/com/google/devtools/build/lib/rules/objc/BazelJ2ObjcLibraryTest.java b/src/test/java/com/google/devtools/build/lib/rules/objc/BazelJ2ObjcLibraryTest.java
index c74e14000d..f617673885 100644
--- a/src/test/java/com/google/devtools/build/lib/rules/objc/BazelJ2ObjcLibraryTest.java
+++ b/src/test/java/com/google/devtools/build/lib/rules/objc/BazelJ2ObjcLibraryTest.java
@@ -794,7 +794,6 @@ public class BazelJ2ObjcLibraryTest extends J2ObjcLibraryTest {
             ImmutableMap.<String, String>of(),
             ImmutableMap.of(),
             DUMMY_ARTIFACT_EXPANDER,
-            null,
             null);
     ByteArrayOutputStream moduleMapStream = new ByteArrayOutputStream();
     ByteArrayOutputStream umbrellaHeaderStream = new ByteArrayOutputStream();
@@ -846,7 +845,6 @@ public class BazelJ2ObjcLibraryTest extends J2ObjcLibraryTest {
             ImmutableMap.<String, String>of(),
             ImmutableMap.of(),
             DUMMY_ARTIFACT_EXPANDER,
-            null,
             null);
 
     ByteArrayOutputStream moduleMapStream = new ByteArrayOutputStream();
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunctionTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunctionTest.java
index 5e5ff1420c..e972020051 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunctionTest.java
@@ -593,6 +593,147 @@ public final class FilesetEntryFunctionTest extends FoundationTestCase {
   }
 
   @Test
+  public void testNestedFileFilesetTraversal() throws Exception {
+    Artifact path1 = getSourceArtifact("foo/bar.file");
+    createFile(path1, "blah");
+    Artifact path2 = getSourceArtifact("foo/baz.file");
+    createFile(path2, "what");
+    FilesetTraversalParams inner1 =
+        FilesetTraversalParamsFactory.fileTraversal(
+            /*ownerLabel=*/ label("//foo"),
+            /*fileToTraverse=*/ path1,
+            PathFragment.create("inner-out1"),
+            /*symlinkBehaviorMode=*/ SymlinkBehavior.COPY,
+            /*pkgBoundaryMode=*/ DONT_CROSS,
+            /*strictFilesetOutput=*/ false);
+    FilesetTraversalParams inner2 =
+        FilesetTraversalParamsFactory.fileTraversal(
+            /*ownerLabel=*/ label("//foo"),
+            /*fileToTraverse=*/ path2,
+            PathFragment.create("inner-out2"),
+            /*symlinkBehaviorMode=*/ SymlinkBehavior.COPY,
+            /*pkgBoundaryMode=*/ DONT_CROSS,
+            /*strictFilesetOutput=*/ false);
+    FilesetTraversalParams outer =
+        FilesetTraversalParamsFactory.nestedTraversal(
+            /*ownerLabel=*/ label("//foo:bar"),
+            /*nested=*/ ImmutableList.of(inner1, inner2),
+            PathFragment.create("outer-out"),
+            /*excludes=*/ null);
+    assertSymlinksCreatedInOrder(
+        outer,
+        symlink("outer-out/inner-out1", rootedPath(path1)),
+        symlink("outer-out/inner-out2", rootedPath(path2)));
+  }
+
+  @Test
+  public void testMultiLevelNesting() throws Exception {
+    Artifact path1 = getSourceArtifact("foo/bar.file");
+    createFile(path1, "blah");
+    Artifact path2 = getSourceArtifact("foo/baz.file");
+    createFile(path2, "what");
+    Artifact path3 = getSourceArtifact("foo/hw.file");
+    createFile(path3, "hello");
+    FilesetTraversalParams inner1 =
+        FilesetTraversalParamsFactory.fileTraversal(
+            /*ownerLabel=*/ label("//foo"),
+            /*fileToTraverse=*/ path1,
+            PathFragment.create("inner-out1"),
+            /*symlinkBehaviorMode=*/ SymlinkBehavior.COPY,
+            /*pkgBoundaryMode=*/ DONT_CROSS,
+            /*strictFilesetOutput=*/ false);
+    FilesetTraversalParams inner2 =
+        FilesetTraversalParamsFactory.fileTraversal(
+            /*ownerLabel=*/ label("//foo"),
+            /*fileToTraverse=*/ path2,
+            PathFragment.create("inner-out2"),
+            /*symlinkBehaviorMode=*/ SymlinkBehavior.COPY,
+            /*pkgBoundaryMode=*/ DONT_CROSS,
+            /*strictFilesetOutput=*/ false);
+    FilesetTraversalParams middle1 =
+        FilesetTraversalParamsFactory.nestedTraversal(
+            /*ownerLabel=*/ label("//foo:middle1"),
+            /*nested=*/ ImmutableList.of(inner1, inner2),
+            PathFragment.create("middle-out1"),
+            /*excludes=*/ null);
+
+    FilesetTraversalParams inner3 =
+        FilesetTraversalParamsFactory.fileTraversal(
+            /*ownerLabel=*/ label("//foo:inner3"),
+            /*fileToTraverse=*/ path3,
+            PathFragment.create("inner-out3"),
+            /*symlinkBehaviorMode=*/ SymlinkBehavior.COPY,
+            /*pkgBoundaryMode=*/ DONT_CROSS,
+            /*strictFilesetOutput=*/ false);
+    FilesetTraversalParams middle2 =
+        FilesetTraversalParamsFactory.nestedTraversal(
+            /*ownerLabel=*/ label("//foo:middle2"),
+            /*nested=*/ ImmutableList.of(inner3),
+            PathFragment.create("middle-out2"),
+            /*excludes=*/ null);
+
+    FilesetTraversalParams outer =
+        FilesetTraversalParamsFactory.nestedTraversal(
+            /*ownerLabel=*/ label("//foo:bar"),
+            /*nested=*/ ImmutableList.of(middle1, middle2),
+            PathFragment.create("outer-out"),
+            /*excludes=*/ null);
+    assertSymlinksCreatedInOrder(
+        outer,
+        symlink("outer-out/middle-out1/inner-out1", rootedPath(path1)),
+        symlink("outer-out/middle-out1/inner-out2", rootedPath(path2)),
+        symlink("outer-out/middle-out2/inner-out3", rootedPath(path3)));
+  }
+
+  private void assertNestedRecursiveFilesetTraversal(boolean useInnerDir) throws Exception {
+    Artifact dir = getSourceArtifact("foo/dir");
+    RootedPath fileA = createFile(childOf(dir, "file.a"), "hello");
+    RootedPath fileB = createFile(childOf(dir, "file.b"), "hello");
+    RootedPath fileC = createFile(childOf(dir, "sub/file.c"), "world");
+
+    FilesetTraversalParams inner =
+        FilesetTraversalParamsFactory.recursiveTraversalOfDirectory(
+            /*ownerLabel=*/ label("//foo"),
+            /*directoryToTraverse=*/ dir,
+            PathFragment.create(useInnerDir ? "inner-dir" : ""),
+            /*excludes=*/ null,
+            /*symlinkBehaviorMode=*/ SymlinkBehavior.COPY,
+            /*pkgBoundaryMode=*/ DONT_CROSS,
+            /*strictFilesetOutput=*/ false);
+    FilesetTraversalParams outer =
+        FilesetTraversalParamsFactory.nestedTraversal(
+            /*ownerLabel=*/ label("//foo"),
+            /*nested=*/ ImmutableList.of(inner),
+            PathFragment.create("outer-dir"),
+            /*excludes=*/ ImmutableSet.of("file.a", "sub/file.c"));
+
+    if (useInnerDir) {
+      assertSymlinksCreatedInOrder(
+          outer,
+          // no file is excluded, since no files from "inner" are top-level in the outer Fileset
+          symlink("outer-dir/inner-dir/file.a", fileA),
+          symlink("outer-dir/inner-dir/file.b", fileB),
+          symlink("outer-dir/inner-dir/sub/file.c", fileC)); // only top-level files are excluded
+    } else {
+      assertSymlinksCreatedInOrder(
+          outer,
+          // file.a can be excluded because it's top-level (there's no output directory for "inner")
+          symlink("outer-dir/file.b", fileB),
+          symlink("outer-dir/sub/file.c", fileC)); // only top-level files could be excluded
+    }
+  }
+
+  @Test
+  public void testNestedRecursiveFilesetTraversalWithInnerDestDir() throws Exception {
+    assertNestedRecursiveFilesetTraversal(true);
+  }
+
+  @Test
+  public void testNestedRecursiveFilesetTraversalWithoutInnerDestDir() throws Exception {
+    assertNestedRecursiveFilesetTraversal(false);
+  }
+
+  @Test
   public void testFileTraversalForDanglingSymlink() throws Exception {
     Artifact linkName = getSourceArtifact("foo/dangling.sym");
     RootedPath linkTarget = createFile(siblingOf(linkName, "target.file"), "blah");
@@ -930,13 +1071,48 @@ public final class FilesetEntryFunctionTest extends FoundationTestCase {
 
   @Test
   public void testFingerprintOfNestedTraversal() throws Exception {
-    Artifact nested1 = getSourceArtifact("a/b");
-    Artifact nested2 = getSourceArtifact("a/c");
+    FilesetTraversalParams n1 =
+        FilesetTraversalParamsFactory.fileTraversal(
+            /*ownerLabel=*/ label("//blah"),
+            /*fileToTraverse=*/ getSourceArtifact("blah/file.a"),
+            PathFragment.create("output-name"),
+            /*symlinkBehaviorMode=*/ SymlinkBehavior.COPY,
+            /*pkgBoundaryMode=*/ DONT_CROSS,
+            /*strictFilesetOutput=*/ false);
+
+    FilesetTraversalParams n2 =
+        FilesetTraversalParamsFactory.fileTraversal(
+            /*ownerLabel=*/ label("//blah"),
+            /*fileToTraverse=*/ getSourceArtifact("meow/file.b"),
+            PathFragment.create("output-name"),
+            /*symlinkBehaviorMode=*/ SymlinkBehavior.COPY,
+            /*pkgBoundaryMode=*/ DONT_CROSS,
+            /*strictFilesetOutput=*/ false);
+    ImmutableList<FilesetTraversalParams> nested1 = ImmutableList.of(n1, n2);
+
+    FilesetTraversalParams n3 =
+        FilesetTraversalParamsFactory.fileTraversal(
+            /*ownerLabel=*/ label("//blah"),
+            /*fileToTraverse=*/ getSourceArtifact("brrr/file.c"),
+            PathFragment.create("output-name"),
+            /*symlinkBehaviorMode=*/ SymlinkBehavior.COPY,
+            /*pkgBoundaryMode=*/ DONT_CROSS,
+            /*strictFilesetOutput=*/ false);
+
+    FilesetTraversalParams n4 =
+        FilesetTraversalParamsFactory.fileTraversal(
+            /*ownerLabel=*/ label("//blah"),
+            /*fileToTraverse=*/ getSourceArtifact("hurr/file.d"),
+            PathFragment.create("output-name"),
+            /*symlinkBehaviorMode=*/ SymlinkBehavior.COPY,
+            /*pkgBoundaryMode=*/ DONT_CROSS,
+            /*strictFilesetOutput=*/ false);
+    ImmutableList<FilesetTraversalParams> nested2 = ImmutableList.of(n3, n4);
 
     new FingerprintTester(
         ImmutableMap.<String, Domain>of(
             "ownerLabel", notPartOfFingerprint("//foo", "//bar"),
-            "nestedArtifact", partOfFingerprint(nested1, nested2),
+            "nested", partOfFingerprint(nested1, nested2),
             "destDir", partOfFingerprint("out1", "out2"),
             "excludes",
                 partOfFingerprint(ImmutableSet.<String>of(), ImmutableSet.<String>of("x")))) {
@@ -945,7 +1121,7 @@ public final class FilesetEntryFunctionTest extends FoundationTestCase {
       FilesetTraversalParams create(Map<String, ?> kwArgs) throws Exception {
         return FilesetTraversalParamsFactory.nestedTraversal(
             label((String) kwArgs.get("ownerLabel")),
-            (Artifact) kwArgs.get("nestedArtifact"),
+            (ImmutableList<FilesetTraversalParams>) kwArgs.get("nested"),
             PathFragment.create((String) kwArgs.get("destDir")),
             (Set<String>) kwArgs.get("excludes"));
       }
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/SkyframeAwareActionTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/SkyframeAwareActionTest.java
index 18f117f43a..3060a08d3e 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/SkyframeAwareActionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/SkyframeAwareActionTest.java
@@ -249,12 +249,11 @@ public class SkyframeAwareActionTest extends TimestampBuilderTestCase {
     }
 
     @Override
-    public Object establishSkyframeDependencies(Environment env)
+    public void establishSkyframeDependencies(Environment env)
         throws ExceptionBase, InterruptedException {
       // Establish some Skyframe dependency. A real action would then use this to compute and
       // cache data for the execute(...) method.
       env.getValue(actionDepKey);
-      return null;
     }
   }
 
@@ -798,9 +797,8 @@ public class SkyframeAwareActionTest extends TimestampBuilderTestCase {
     registerAction(
         new SingleOutputSkyframeAwareAction(genFile1, genFile2) {
           @Override
-          public Object establishSkyframeDependencies(Environment env) throws ExceptionBase {
+          public void establishSkyframeDependencies(Environment env) throws ExceptionBase {
             assertThat(env.valuesMissing()).isFalse();
-            return null;
           }
 
           @Override
diff --git a/src/test/java/com/google/devtools/build/lib/standalone/StandaloneSpawnStrategyTest.java b/src/test/java/com/google/devtools/build/lib/standalone/StandaloneSpawnStrategyTest.java
index ccccc612e1..da31f120d2 100644
--- a/src/test/java/com/google/devtools/build/lib/standalone/StandaloneSpawnStrategyTest.java
+++ b/src/test/java/com/google/devtools/build/lib/standalone/StandaloneSpawnStrategyTest.java
@@ -194,8 +194,7 @@ public class StandaloneSpawnStrategyTest {
         ImmutableMap.<String, String>of(),
         ImmutableMap.of(),
         SIMPLE_ARTIFACT_EXPANDER,
-        /*actionFileSystem=*/ null,
-        /*skyframeDepsResult=*/ null);
+        /*actionFileSystem=*/ null);
   }
 
   @Test