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diff --git a/java/com/google/gerrit/server/submit/MergeSuperSet.java b/java/com/google/gerrit/server/submit/MergeSuperSet.java
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+// Copyright (C) 2015 The Android Open Source Project
+//
+// 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.gerrit.server.submit;
+
+import static com.google.common.base.Preconditions.checkState;
+import static java.util.Objects.requireNonNull;
+
+import com.google.common.base.Strings;
+import com.google.common.collect.Iterables;
+import com.google.gerrit.extensions.registration.DynamicItem;
+import com.google.gerrit.extensions.restapi.AuthException;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.config.GerritServerConfig;
+import com.google.gerrit.server.logging.TraceContext;
+import com.google.gerrit.server.permissions.ChangePermission;
+import com.google.gerrit.server.permissions.PermissionBackend;
+import com.google.gerrit.server.permissions.PermissionBackendException;
+import com.google.gerrit.server.plugincontext.PluginContext;
+import com.google.gerrit.server.project.ProjectCache;
+import com.google.gerrit.server.project.ProjectState;
+import com.google.gerrit.server.query.change.ChangeData;
+import com.google.gerrit.server.query.change.InternalChangeQuery;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import org.eclipse.jgit.lib.Config;
+
+/**
+ * Calculates the minimal superset of changes required to be merged.
+ *
+ * <p>This includes all parents between a change and the tip of its target branch for the
+ * merging/rebasing submit strategies. For the cherry-pick strategy no additional changes are
+ * included.
+ *
+ * <p>If change.submitWholeTopic is enabled, also all changes of the topic and their parents are
+ * included.
+ */
+public class MergeSuperSet {
+
+  private final Provider<InternalChangeQuery> queryProvider;
+  private final Provider<MergeOpRepoManager> repoManagerProvider;
+  private final DynamicItem<MergeSuperSetComputation> mergeSuperSetComputation;
+  private final PermissionBackend permissionBackend;
+  private final Config cfg;
+  private final ProjectCache projectCache;
+
+  private MergeOpRepoManager orm;
+  private boolean closeOrm;
+
+  @Inject
+  MergeSuperSet(
+      @GerritServerConfig Config cfg,
+      Provider<InternalChangeQuery> queryProvider,
+      Provider<MergeOpRepoManager> repoManagerProvider,
+      DynamicItem<MergeSuperSetComputation> mergeSuperSetComputation,
+      PermissionBackend permissionBackend,
+      ProjectCache projectCache) {
+    this.cfg = cfg;
+    this.queryProvider = queryProvider;
+    this.repoManagerProvider = repoManagerProvider;
+    this.mergeSuperSetComputation = mergeSuperSetComputation;
+    this.permissionBackend = permissionBackend;
+    this.projectCache = projectCache;
+  }
+
+  public static boolean wholeTopicEnabled(Config config) {
+    return config.getBoolean("change", null, "submitWholeTopic", false);
+  }
+
+  public MergeSuperSet setMergeOpRepoManager(MergeOpRepoManager orm) {
+    checkState(this.orm == null);
+    this.orm = requireNonNull(orm);
+    closeOrm = false;
+    return this;
+  }
+
+  public ChangeSet completeChangeSet(ReviewDb db, Change change, CurrentUser user)
+      throws IOException, OrmException, PermissionBackendException {
+    try {
+      if (orm == null) {
+        orm = repoManagerProvider.get();
+        closeOrm = true;
+      }
+      List<ChangeData> cds = queryProvider.get().byLegacyChangeId(change.getId());
+      checkState(cds.size() == 1, "Expected exactly one ChangeData, got " + cds.size());
+      ChangeData cd = Iterables.getFirst(cds, null);
+
+      boolean visible = false;
+      if (cd != null) {
+        ProjectState projectState = projectCache.checkedGet(cd.project());
+
+        if (projectState.statePermitsRead()) {
+          try {
+            permissionBackend.user(user).change(cd).database(db).check(ChangePermission.READ);
+            visible = true;
+          } catch (AuthException e) {
+            // Do nothing.
+          }
+        }
+      }
+
+      ChangeSet changeSet = new ChangeSet(cd, visible);
+      if (wholeTopicEnabled(cfg)) {
+        return completeChangeSetIncludingTopics(db, changeSet, user);
+      }
+      try (TraceContext traceContext = PluginContext.newTrace(mergeSuperSetComputation)) {
+        return mergeSuperSetComputation.get().completeWithoutTopic(db, orm, changeSet, user);
+      }
+    } finally {
+      if (closeOrm && orm != null) {
+        orm.close();
+        orm = null;
+      }
+    }
+  }
+
+  /**
+   * Completes {@code changeSet} with any additional changes from its topics
+   *
+   * <p>{@link #completeChangeSetIncludingTopics} calls this repeatedly, alternating with {@link
+   * MergeSuperSetComputation#completeWithoutTopic(ReviewDb, MergeOpRepoManager, ChangeSet,
+   * CurrentUser)}, to discover what additional changes should be submitted with a change until the
+   * set stops growing.
+   *
+   * <p>{@code topicsSeen} and {@code visibleTopicsSeen} keep track of topics already explored to
+   * avoid wasted work.
+   *
+   * @return the resulting larger {@link ChangeSet}
+   */
+  private ChangeSet topicClosure(
+      ReviewDb db,
+      ChangeSet changeSet,
+      CurrentUser user,
+      Set<String> topicsSeen,
+      Set<String> visibleTopicsSeen)
+      throws OrmException, PermissionBackendException, IOException {
+    List<ChangeData> visibleChanges = new ArrayList<>();
+    List<ChangeData> nonVisibleChanges = new ArrayList<>();
+
+    for (ChangeData cd : changeSet.changes()) {
+      visibleChanges.add(cd);
+      String topic = cd.change().getTopic();
+      if (Strings.isNullOrEmpty(topic) || visibleTopicsSeen.contains(topic)) {
+        continue;
+      }
+      for (ChangeData topicCd : byTopicOpen(topic)) {
+        if (canRead(db, user, topicCd)) {
+          visibleChanges.add(topicCd);
+        } else {
+          nonVisibleChanges.add(topicCd);
+        }
+      }
+      topicsSeen.add(topic);
+      visibleTopicsSeen.add(topic);
+    }
+    for (ChangeData cd : changeSet.nonVisibleChanges()) {
+      nonVisibleChanges.add(cd);
+      String topic = cd.change().getTopic();
+      if (Strings.isNullOrEmpty(topic) || topicsSeen.contains(topic)) {
+        continue;
+      }
+      for (ChangeData topicCd : byTopicOpen(topic)) {
+        nonVisibleChanges.add(topicCd);
+      }
+      topicsSeen.add(topic);
+    }
+    return new ChangeSet(visibleChanges, nonVisibleChanges);
+  }
+
+  private ChangeSet completeChangeSetIncludingTopics(
+      ReviewDb db, ChangeSet changeSet, CurrentUser user)
+      throws IOException, OrmException, PermissionBackendException {
+    Set<String> topicsSeen = new HashSet<>();
+    Set<String> visibleTopicsSeen = new HashSet<>();
+    int oldSeen;
+    int seen;
+
+    changeSet = topicClosure(db, changeSet, user, topicsSeen, visibleTopicsSeen);
+    seen = topicsSeen.size() + visibleTopicsSeen.size();
+
+    do {
+      oldSeen = seen;
+      try (TraceContext traceContext = PluginContext.newTrace(mergeSuperSetComputation)) {
+        changeSet = mergeSuperSetComputation.get().completeWithoutTopic(db, orm, changeSet, user);
+      }
+      changeSet = topicClosure(db, changeSet, user, topicsSeen, visibleTopicsSeen);
+      seen = topicsSeen.size() + visibleTopicsSeen.size();
+    } while (seen != oldSeen);
+    return changeSet;
+  }
+
+  private List<ChangeData> byTopicOpen(String topic) throws OrmException {
+    return queryProvider.get().byTopicOpen(topic);
+  }
+
+  private boolean canRead(ReviewDb db, CurrentUser user, ChangeData cd)
+      throws PermissionBackendException, IOException {
+    ProjectState projectState = projectCache.checkedGet(cd.project());
+    if (projectState == null || !projectState.statePermitsRead()) {
+      return false;
+    }
+
+    try {
+      permissionBackend.user(user).change(cd).database(db).check(ChangePermission.READ);
+      return true;
+    } catch (AuthException e) {
+      return false;
+    }
+  }
+}