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diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactValue.java
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+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactValue.java
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+// Copyright 2014 Google Inc. 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.base.Function;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.Collections2;
+import com.google.common.collect.Iterables;
+import com.google.devtools.build.lib.actions.Artifact;
+import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
+import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
+import com.google.devtools.build.skyframe.SkyKey;
+import com.google.devtools.build.skyframe.SkyValue;
+
+import java.util.Collection;
+
+/**
+ * A value representing an artifact. Source artifacts are checked for existence, while output
+ * artifacts imply creation of the output file.
+ *
+ * <p>There are effectively two kinds of output artifact values. The first corresponds to an
+ * ordinary artifact {@link FileArtifactValue}. It stores the relevant data for the artifact --
+ * digest/mtime and size. The second corresponds to an "aggregating" artifact -- the output of an
+ * aggregating middleman action. It stores the relevant data of all its inputs.
+ */
+@Immutable
+@ThreadSafe
+public abstract class ArtifactValue implements SkyValue {
+
+  @ThreadSafe
+  static SkyKey key(Artifact artifact, boolean isMandatory) {
+    return new SkyKey(SkyFunctions.ARTIFACT, artifact.isSourceArtifact()
+        ? new OwnedArtifact(artifact, isMandatory)
+        : new OwnedArtifact(artifact));
+  }
+
+  private static final Function<Artifact, SkyKey> TO_MANDATORY_KEY =
+      new Function<Artifact, SkyKey>() {
+        @Override
+        public SkyKey apply(Artifact artifact) {
+          return key(artifact, true);
+        }
+      };
+
+  @ThreadSafe
+  public static Iterable<SkyKey> mandatoryKeys(Iterable<Artifact> artifacts) {
+    return Iterables.transform(artifacts, TO_MANDATORY_KEY);
+  }
+
+  private static final Function<OwnedArtifact, Artifact> TO_ARTIFACT =
+      new Function<OwnedArtifact, Artifact>() {
+    @Override
+    public Artifact apply(OwnedArtifact key) {
+      return key.getArtifact();
+    }
+  };
+
+  public static Collection<Artifact> artifacts(Collection<? extends OwnedArtifact> keys) {
+    return Collections2.transform(keys, TO_ARTIFACT);
+  }
+
+  public static Artifact artifact(SkyKey key) {
+    return TO_ARTIFACT.apply((OwnedArtifact) key.argument());
+  }
+
+  /**
+   * Artifacts are compared using just their paths, but in Skyframe, the configured target that owns
+   * an artifact must also be part of the comparison. For example, suppose we build //foo:foo in
+   * configurationA, yielding artifact foo.out. If we change the configuration to configurationB in
+   * such a way that the path to the artifact does not change, requesting foo.out from the graph
+   * will result in the value entry for foo.out under configurationA being returned. This would
+   * prevent caching the graph in different configurations, and also causes big problems with change
+   * pruning, which assumes the invariant that a value's first dependency will always be the same.
+   * In this case, the value entry's old dependency on //foo:foo in configurationA would cause it to
+   * request (//foo:foo, configurationA) from the graph, causing an undesired re-analysis of
+   * (//foo:foo, configurationA).
+   *
+   * <p>In order to prevent that, instead of using Artifacts as keys in the graph, we use
+   * OwnedArtifacts, which compare for equality using both the Artifact, and the owner. The effect
+   * is functionally that of making Artifact.equals() check the owner, but only within Skyframe,
+   * since outside of Skyframe it is quite crucial that Artifacts with different owners be able to
+   * compare equal.
+   */
+  public static class OwnedArtifact {
+    private final Artifact artifact;
+    // Always true for derived artifacts.
+    private final boolean isMandatory;
+
+    /** Constructs an OwnedArtifact wrapper for a source artifact. */
+    private OwnedArtifact(Artifact sourceArtifact, boolean mandatory) {
+      Preconditions.checkArgument(sourceArtifact.isSourceArtifact());
+      this.artifact = Preconditions.checkNotNull(sourceArtifact);
+      this.isMandatory = mandatory;
+    }
+
+    /**
+     * Constructs an OwnedArtifact wrapper for a derived artifact. The mandatory attribute is
+     * not needed because a derived artifact must be a mandatory input for some action in order to
+     * ensure that it is built in the first place. If it fails to build, then that fact is cached
+     * in the node, so any action that has it as a non-mandatory input can retrieve that
+     * information from the node.
+     */
+    private OwnedArtifact(Artifact derivedArtifact) {
+      this.artifact = Preconditions.checkNotNull(derivedArtifact);
+      Preconditions.checkArgument(!derivedArtifact.isSourceArtifact(), derivedArtifact);
+      this.isMandatory = true; // Unused.
+    }
+
+    @Override
+    public int hashCode() {
+      int initialHash = artifact.hashCode() +  artifact.getArtifactOwner().hashCode();
+      return isMandatory ? initialHash : 47 * initialHash + 1;
+    }
+
+    @Override
+    public boolean equals(Object that) {
+      if (this == that) {
+        return true;
+      }
+      if (!(that instanceof OwnedArtifact)) {
+        return false;
+      }
+      OwnedArtifact thatOwnedArtifact = ((OwnedArtifact) that);
+      Artifact thatArtifact = thatOwnedArtifact.artifact;
+      return artifact.equals(thatArtifact)
+          && artifact.getArtifactOwner().equals(thatArtifact.getArtifactOwner())
+          && isMandatory == thatOwnedArtifact.isMandatory;
+    }
+
+    Artifact getArtifact() {
+      return artifact;
+    }
+
+    /**
+     * Returns whether the artifact is a mandatory input of its requesting action. May only be
+     * called for source artifacts, since a derived artifact must be a mandatory input of some
+     * action in order to have been built in the first place.
+     */
+    public boolean isMandatory() {
+      Preconditions.checkState(artifact.isSourceArtifact(), artifact);
+      return isMandatory;
+    }
+
+    @Override
+    public String toString() {
+      return artifact.prettyPrint() + " " + artifact.getArtifactOwner();
+    }
+  }
+}