1 files changed, 198 insertions, 0 deletions
diff --git a/java/com/google/gerrit/server/patch/AutoMerger.java b/java/com/google/gerrit/server/patch/AutoMerger.java
new file mode 100644
index 0000000000..285c37d103
--- /dev/null
+++ b/java/com/google/gerrit/server/patch/AutoMerger.java
@@ -0,0 +1,198 @@
+// Copyright (C) 2016 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.patch;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+import com.google.common.flogger.FluentLogger;
+import com.google.gerrit.common.Nullable;
+import com.google.gerrit.reviewdb.client.RefNames;
+import com.google.gerrit.server.GerritPersonIdent;
+import com.google.gerrit.server.UsedAt;
+import com.google.gerrit.server.config.GerritServerConfig;
+import com.google.gerrit.server.git.InMemoryInserter;
+import com.google.gerrit.server.git.MergeUtil;
+import com.google.inject.Inject;
+import java.io.IOException;
+import org.eclipse.jgit.dircache.DirCache;
+import org.eclipse.jgit.lib.CommitBuilder;
+import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectInserter;
+import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.lib.PersonIdent;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.RefUpdate;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.merge.ResolveMerger;
+import org.eclipse.jgit.merge.ThreeWayMergeStrategy;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevObject;
+import org.eclipse.jgit.revwalk.RevWalk;
+
+public class AutoMerger {
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
+  @UsedAt(UsedAt.Project.GOOGLE)
+  public static boolean cacheAutomerge(Config cfg) {
+    return cfg.getBoolean("change", null, "cacheAutomerge", true);
+  }
+
+  private final PersonIdent gerritIdent;
+  private final boolean save;
+
+  @Inject
+  AutoMerger(@GerritServerConfig Config cfg, @GerritPersonIdent PersonIdent gerritIdent) {
+    save = cacheAutomerge(cfg);
+    this.gerritIdent = gerritIdent;
+  }
+
+  /**
+   * Perform an auto-merge of the parents of the given merge commit.
+   *
+   * @return auto-merge commit or {@code null} if an auto-merge commit couldn't be created. Headers
+   *     of the returned RevCommit are parsed.
+   */
+  public RevCommit merge(
+      Repository repo,
+      RevWalk rw,
+      ObjectInserter ins,
+      RevCommit merge,
+      ThreeWayMergeStrategy mergeStrategy)
+      throws IOException {
+    checkArgument(rw.getObjectReader().getCreatedFromInserter() == ins);
+    InMemoryInserter tmpIns = null;
+    if (ins instanceof InMemoryInserter) {
+      // Caller gave us an in-memory inserter, so ensure anything we write from
+      // this method is visible to them.
+      tmpIns = (InMemoryInserter) ins;
+    } else if (!save) {
+      // If we don't plan on saving results, use a fully in-memory inserter.
+      // Using just a non-flushing wrapper is not sufficient, since in
+      // particular DfsInserter might try to write to storage after exceeding an
+      // internal buffer size.
+      tmpIns = new InMemoryInserter(rw.getObjectReader());
+    }
+
+    rw.parseHeaders(merge);
+    String refName = RefNames.refsCacheAutomerge(merge.name());
+    Ref ref = repo.getRefDatabase().exactRef(refName);
+    if (ref != null && ref.getObjectId() != null) {
+      RevObject obj = rw.parseAny(ref.getObjectId());
+      if (obj instanceof RevCommit) {
+        return (RevCommit) obj;
+      }
+      return commit(repo, rw, tmpIns, ins, refName, obj, merge);
+    }
+
+    ResolveMerger m = (ResolveMerger) mergeStrategy.newMerger(repo, true);
+    DirCache dc = DirCache.newInCore();
+    m.setDirCache(dc);
+    m.setObjectInserter(tmpIns == null ? new NonFlushingWrapper(ins) : tmpIns);
+
+    boolean couldMerge;
+    try {
+      couldMerge = m.merge(merge.getParents());
+    } catch (IOException | RuntimeException e) {
+      // It is not safe to continue further down in this method as throwing
+      // an exception most likely means that the merge tree was not created
+      // and m.getMergeResults() is empty. This would mean that all paths are
+      // unmerged and Gerrit UI would show all paths in the patch list.
+      logger.atWarning().withCause(e).log("Error attempting automerge %s", refName);
+      return null;
+    }
+
+    ObjectId treeId;
+    if (couldMerge) {
+      treeId = m.getResultTreeId();
+    } else {
+      treeId =
+          MergeUtil.mergeWithConflicts(
+              rw,
+              ins,
+              dc,
+              "HEAD",
+              merge.getParent(0),
+              "BRANCH",
+              merge.getParent(1),
+              m.getMergeResults());
+    }
+
+    return commit(repo, rw, tmpIns, ins, refName, treeId, merge);
+  }
+
+  private RevCommit commit(
+      Repository repo,
+      RevWalk rw,
+      @Nullable InMemoryInserter tmpIns,
+      ObjectInserter ins,
+      String refName,
+      ObjectId tree,
+      RevCommit merge)
+      throws IOException {
+    rw.parseHeaders(merge);
+    // For maximum stability, choose a single ident using the committer time of
+    // the input commit, using the server name and timezone.
+    PersonIdent ident =
+        new PersonIdent(
+            gerritIdent, merge.getCommitterIdent().getWhen(), gerritIdent.getTimeZone());
+    CommitBuilder cb = new CommitBuilder();
+    cb.setAuthor(ident);
+    cb.setCommitter(ident);
+    cb.setTreeId(tree);
+    cb.setMessage("Auto-merge of " + merge.name() + '\n');
+    for (RevCommit p : merge.getParents()) {
+      cb.addParentId(p);
+    }
+
+    if (!save) {
+      checkArgument(tmpIns != null);
+      try (ObjectReader tmpReader = tmpIns.newReader();
+          RevWalk tmpRw = new RevWalk(tmpReader)) {
+        return tmpRw.parseCommit(tmpIns.insert(cb));
+      }
+    }
+
+    checkArgument(tmpIns == null);
+    checkArgument(!(ins instanceof InMemoryInserter));
+    ObjectId commitId = ins.insert(cb);
+    ins.flush();
+
+    RefUpdate ru = repo.updateRef(refName);
+    ru.setNewObjectId(commitId);
+    ru.disableRefLog();
+    ru.forceUpdate();
+    return rw.parseCommit(commitId);
+  }
+
+  private static class NonFlushingWrapper extends ObjectInserter.Filter {
+    private final ObjectInserter ins;
+
+    private NonFlushingWrapper(ObjectInserter ins) {
+      this.ins = ins;
+    }
+
+    @Override
+    protected ObjectInserter delegate() {
+      return ins;
+    }
+
+    @Override
+    public void flush() {}
+
+    @Override
+    public void close() {}
+  }
+}