Add equality tests for FrontierNodeVersion.

The frontier node version's representation is uniquely identified by the composition of its components, i.e. the precomputed byte array. So we can base the object's equality on that.

PiperOrigin-RevId: 681860462
Change-Id: I47ae11096b1d123219cca8c27f32c6387f9157da

src/main/java/com/google/devtools/build/lib/skyframe/serialization/SkyValueRetriever.java

@@ -33,6 +33,7 @@
 import com.google.devtools.build.skyframe.SkyValue;
 import com.google.protobuf.ByteString;
 import java.io.IOException;
+import java.util.Arrays;
 import java.util.concurrent.ExecutionException;
 
 /** Fetches remotely stored {@link SkyValue}s by {@link SkyKey}. */
@@ -349,18 +350,28 @@ public FrontierNodeVersion(
               this.blazeInstallMD5Fingerprint);
     }
 
-    @SuppressWarnings("unused")
-    public byte[] getTopLevelConfigFingerprint() {
-      return topLevelConfigFingerprint;
-    }
-
-    @SuppressWarnings("unused")
-    public byte[] getDirectoryMatcherFingerprint() {
-      return directoryMatcherFingerprint;
+    public byte[] getPrecomputedFingerprint() {
+      return precomputedFingerprint;
     }
 
     public byte[] concat(byte[] input) {
       return Bytes.concat(precomputedFingerprint, input);
     }
+
+    @Override
+    public int hashCode() {
+      return Arrays.hashCode(precomputedFingerprint);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (this == obj) {
+        return true;
+      }
+      if (!(obj instanceof FrontierNodeVersion that)) {
+        return false;
+      }
+      return Arrays.equals(precomputedFingerprint, that.precomputedFingerprint);
+    }
   }
 }

src/test/java/com/google/devtools/build/lib/skyframe/serialization/SkyValueRetrieverTest.java

@@ -544,6 +544,50 @@ public void exceptionWhileWaitingForResult_throwsException() throws Exception {
     assertThat(thrown).hasCauseThat().hasMessageThat().contains("error setting value");
   }
 
+  @Test
+  public void frontierNodeVersions_areEqual_ifTupleComponentsAreEqual() {
+    var first =
+        new FrontierNodeVersion("foo", ByteString.copyFromUtf8("bar"), HashCode.fromInt(42));
+    var second =
+        new FrontierNodeVersion("foo", ByteString.copyFromUtf8("bar"), HashCode.fromInt(42));
+
+    assertThat(first.getPrecomputedFingerprint()).isEqualTo(second.getPrecomputedFingerprint());
+    assertThat(first).isEqualTo(second);
+  }
+
+  @Test
+  public void frontierNodeVersions_areNotEqual_ifTopLevelConfigChecksumIsDifferent() {
+    var first =
+        new FrontierNodeVersion("foo", ByteString.copyFromUtf8("bar"), HashCode.fromInt(42));
+    var second =
+        new FrontierNodeVersion("CHANGED", ByteString.copyFromUtf8("bar"), HashCode.fromInt(42));
+
+    assertThat(first.getPrecomputedFingerprint()).isNotEqualTo(second.getPrecomputedFingerprint());
+    assertThat(first).isNotEqualTo(second);
+  }
+
+  @Test
+  public void frontierNodeVersions_areNotEqual_ifActiveDirectoriesAreDifferent() {
+    var first =
+        new FrontierNodeVersion("foo", ByteString.copyFromUtf8("bar"), HashCode.fromInt(42));
+    var second =
+        new FrontierNodeVersion("foo", ByteString.copyFromUtf8("CHANGED"), HashCode.fromInt(42));
+
+    assertThat(first.getPrecomputedFingerprint()).isNotEqualTo(second.getPrecomputedFingerprint());
+    assertThat(first).isNotEqualTo(second);
+  }
+
+  @Test
+  public void frontierNodeVersions_areNotEqual_ifBlazeInstallMD5IsDifferent() {
+    var first =
+        new FrontierNodeVersion("foo", ByteString.copyFromUtf8("bar"), HashCode.fromInt(42));
+    var second =
+        new FrontierNodeVersion("foo", ByteString.copyFromUtf8("bar"), HashCode.fromInt(9000));
+
+    assertThat(first.getPrecomputedFingerprint()).isNotEqualTo(second.getPrecomputedFingerprint());
+    assertThat(first).isNotEqualTo(second);
+  }
+
   // ---------- Begin SerializationStateProvider implementation ----------
   @Override
   public SerializationState getSerializationState() {