1 files changed, 30 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/actions/Artifact.java b/src/main/java/com/google/devtools/build/lib/actions/Artifact.java
index e48740b3a3..fb4f1edb37 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/Artifact.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/Artifact.java
@@ -55,6 +55,7 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Comparator;
 import java.util.List;
+import java.util.Map;
 import java.util.Objects;
 import javax.annotation.Nullable;
 
@@ -172,6 +173,35 @@ public class Artifact
     }
   }
 
+  /** Implementation of {@link ArtifactExpander} */
+  public static class ArtifactExpanderImpl implements ArtifactExpander {
+    private final Map<Artifact, Collection<Artifact>> expandedInputs;
+    private final Map<Artifact, ImmutableList<FilesetOutputSymlink>> expandedFilesets;
+
+    public ArtifactExpanderImpl(
+        Map<Artifact, Collection<Artifact>> expandedInputMiddlemen,
+        Map<Artifact, ImmutableList<FilesetOutputSymlink>> expandedFilesets) {
+      this.expandedInputs = expandedInputMiddlemen;
+      this.expandedFilesets = expandedFilesets;
+    }
+
+    @Override
+    public void expand(Artifact artifact, Collection<? super Artifact> output) {
+      Preconditions.checkState(
+          artifact.isMiddlemanArtifact() || artifact.isTreeArtifact(), artifact);
+      Collection<Artifact> result = expandedInputs.get(artifact);
+      if (result != null) {
+        output.addAll(result);
+      }
+    }
+
+    @Override
+    public ImmutableList<FilesetOutputSymlink> getFileset(Artifact artifact) {
+      Preconditions.checkState(artifact.isFileset());
+      return Preconditions.checkNotNull(expandedFilesets.get(artifact));
+    }
+  }
+
   public static final ImmutableList<Artifact> NO_ARTIFACTS = ImmutableList.of();
 
   /** A Predicate that evaluates to true if the Artifact is not a middleman artifact. */