// 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 static java.nio.charset.StandardCharsets.UTF_8;
import com.google.gerrit.common.Nullable;
import com.google.gerrit.reviewdb.client.RefNames;
import com.google.gerrit.server.GerritPersonIdent;
import com.google.gerrit.server.config.GerritServerConfig;
import com.google.gerrit.server.git.InMemoryInserter;
import com.google.inject.Inject;
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;
import org.eclipse.jgit.diff.Sequence;
import org.eclipse.jgit.dircache.DirCache;
import org.eclipse.jgit.dircache.DirCacheBuilder;
import org.eclipse.jgit.dircache.DirCacheEntry;
import org.eclipse.jgit.lib.CommitBuilder;
import org.eclipse.jgit.lib.Config;
import org.eclipse.jgit.lib.Constants;
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.MergeFormatter;
import org.eclipse.jgit.merge.MergeResult;
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;
import org.eclipse.jgit.util.TemporaryBuffer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class AutoMerger {
private static final Logger log = LoggerFactory.getLogger(AutoMerger.class);
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,
final 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 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.
log.warn("Error attempting automerge " + refName, e);
return null;
}
ObjectId treeId;
if (couldMerge) {
treeId = m.getResultTreeId();
} else {
RevCommit ours = merge.getParent(0);
RevCommit theirs = merge.getParent(1);
rw.parseBody(ours);
rw.parseBody(theirs);
String oursMsg = ours.getShortMessage();
String theirsMsg = theirs.getShortMessage();
String oursName =
String.format(
"HEAD (%s %s)",
ours.abbreviate(6).name(), oursMsg.substring(0, Math.min(oursMsg.length(), 60)));
String theirsName =
String.format(
"BRANCH (%s %s)",
theirs.abbreviate(6).name(),
theirsMsg.substring(0, Math.min(theirsMsg.length(), 60)));
MergeFormatter fmt = new MergeFormatter();
Map<String, MergeResult<? extends Sequence>> r = m.getMergeResults();
Map<String, ObjectId> resolved = new HashMap<>();
for (Map.Entry<String, MergeResult<? extends Sequence>> entry : r.entrySet()) {
MergeResult<? extends Sequence> p = entry.getValue();
try (TemporaryBuffer buf = new TemporaryBuffer.LocalFile(null, 10 * 1024 * 1024)) {
fmt.formatMerge(buf, p, "BASE", oursName, theirsName, UTF_8.name());
buf.close();
try (InputStream in = buf.openInputStream()) {
resolved.put(entry.getKey(), ins.insert(Constants.OBJ_BLOB, buf.length(), in));
}
}
}
DirCacheBuilder builder = dc.builder();
int cnt = dc.getEntryCount();
for (int i = 0; i < cnt; ) {
DirCacheEntry entry = dc.getEntry(i);
if (entry.getStage() == 0) {
builder.add(entry);
i++;
continue;
}
int next = dc.nextEntry(i);
String path = entry.getPathString();
DirCacheEntry res = new DirCacheEntry(path);
if (resolved.containsKey(path)) {
// For a file with content merge conflict that we produced a result
// above on, collapse the file down to a single stage 0 with just
// the blob content, and a randomly selected mode (the lowest stage,
// which should be the merge base, or ours).
res.setFileMode(entry.getFileMode());
res.setObjectId(resolved.get(path));
} else if (next == i + 1) {
// If there is exactly one stage present, shouldn't be a conflict...
res.setFileMode(entry.getFileMode());
res.setObjectId(entry.getObjectId());
} else if (next == i + 2) {
// Two stages suggests a delete/modify conflict. Pick the higher
// stage as the automatic result.
entry = dc.getEntry(i + 1);
res.setFileMode(entry.getFileMode());
res.setObjectId(entry.getObjectId());
} else {
// 3 stage conflict, no resolve above
// Punt on the 3-stage conflict and show the base, for now.
res.setFileMode(entry.getFileMode());
res.setObjectId(entry.getObjectId());
}
builder.add(res);
i = next;
}
builder.finish();
treeId = dc.writeTree(ins);
}
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() {}
}
}