Override getPatches() in LargeObjectTombstone

Previously, adding a LargeObjectTombstone to the PatchListCache would
fail because PatchListWeigher could not calculate the weight of the
tombstone because patches was null. Overriding getPatches() fixes this
problem.

This commit also adds a test to check that LargeObjectTombstones are
cached as expected.

Change-Id: I843e8dbdfdc477b2f361305802837b4d10cb863d

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/change/PatchListCacheIT.java

@@ -19,6 +19,7 @@ import static com.google.gerrit.acceptance.GitUtil.getChangeId;
 import static com.google.gerrit.acceptance.GitUtil.pushHead;
 import static java.nio.charset.StandardCharsets.UTF_8;
 
+import com.google.common.cache.Cache;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
 import com.google.gerrit.acceptance.AbstractDaemonTest;
@@ -29,11 +30,14 @@ import com.google.gerrit.reviewdb.client.Patch.ChangeType;
 import com.google.gerrit.server.patch.IntraLineDiff;
 import com.google.gerrit.server.patch.IntraLineDiffArgs;
 import com.google.gerrit.server.patch.IntraLineDiffKey;
+import com.google.gerrit.server.patch.PatchList;
 import com.google.gerrit.server.patch.PatchListCache;
+import com.google.gerrit.server.patch.PatchListCacheImpl;
 import com.google.gerrit.server.patch.PatchListEntry;
 import com.google.gerrit.server.patch.PatchListKey;
 import com.google.gerrit.server.patch.Text;
 import com.google.inject.Inject;
+import com.google.inject.name.Named;
 import java.util.ArrayList;
 import java.util.List;
 import org.eclipse.jgit.diff.Edit;
@@ -53,6 +57,10 @@ public class PatchListCacheIT extends AbstractDaemonTest {
 
   @Inject private PatchListCache patchListCache;
 
+  @Inject
+  @Named("diff")
+  private Cache<PatchListKey, PatchList> abstractPatchListCache;
+
   @Test
   public void listPatchesAgainstBase() throws Exception {
     commitBuilder().add(FILE_D, "4").message(SUBJECT_1).create();
@@ -204,6 +212,15 @@ public class PatchListCacheIT extends AbstractDaemonTest {
     assertThat(intraLineDiff.getEdits()).containsExactly(originalEdit);
   }
 
+  @Test
+  public void largeObjectTombstoneGetsCached() {
+    PatchListKey key = PatchListKey.againstDefaultBase(ObjectId.zeroId(), Whitespace.IGNORE_ALL);
+    PatchListCacheImpl.LargeObjectTombstone tombstone =
+        new PatchListCacheImpl.LargeObjectTombstone();
+    abstractPatchListCache.put(key, tombstone);
+    assertThat(abstractPatchListCache.getIfPresent(key)).isSameAs(tombstone);
+  }
+
   private static void assertAdded(String expectedNewName, PatchListEntry e) {
     assertName(expectedNewName, e);
     assertThat(e.getChangeType()).isEqualTo(ChangeType.ADDED);

gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListCacheImpl.java

@@ -17,7 +17,9 @@ package com.google.gerrit.server.patch;
 
 import static com.google.gerrit.server.patch.DiffSummaryLoader.toDiffSummary;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.cache.Cache;
+import com.google.common.collect.ImmutableList;
 import com.google.common.util.concurrent.UncheckedExecutionException;
 import com.google.gerrit.extensions.client.DiffPreferencesInfo.Whitespace;
 import com.google.gerrit.reviewdb.client.Change;
@@ -29,6 +31,7 @@ import com.google.inject.Inject;
 import com.google.inject.Module;
 import com.google.inject.Singleton;
 import com.google.inject.name.Named;
+import java.util.List;
 import java.util.concurrent.ExecutionException;
 import org.eclipse.jgit.errors.LargeObjectException;
 import org.eclipse.jgit.lib.Config;
@@ -190,9 +193,20 @@ public class PatchListCacheImpl implements PatchListCache {
   }
 
   /** Used to cache negative results in {@code fileCache}. */
-  private class LargeObjectTombstone extends PatchList {
+  @VisibleForTesting
+  public static class LargeObjectTombstone extends PatchList {
     private static final long serialVersionUID = 1L;
 
-    private LargeObjectTombstone() {}
+    @VisibleForTesting
+    public LargeObjectTombstone() {}
+
+    /**
+     * Return an empty list to prevent {@link NullPointerException}s inside of {@link
+     * PatchListWeigher}.
+     */
+    @Override
+    public List<PatchListEntry> getPatches() {
+      return ImmutableList.of();
+    }
   }
 }