java/com/google/gerrit/server/patch/AutoMerger.java - gerrit - Git at Google

 // 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.base.Throwables;
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.common.UsedAt;
 import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.git.LockFailureException;
 import com.google.gerrit.server.GerritPersonIdent;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.git.InMemoryInserter;
 import com.google.gerrit.server.git.MergeUtil;
 import com.google.gerrit.server.update.RetryHelper;
 import com.google.gerrit.server.update.RetryableAction.ActionType;
 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;

 /**
  * Utility class for creating an auto-merge commit of a merge commit.
  *
  * <p>An auto-merge commit is the result of merging the 2 parents of a merge commit automatically.
  * If there are conflicts the auto-merge commit contains Git conflict markers that indicate these
  * conflicts.
  *
  * <p>Creating auto-merge commits for octopus merges (merge commits with more than 2 parents) is not
  * supported. In this case the auto-merge is created between the first 2 parent commits.
  *
  * <p>All created auto-merge commits are stored in the repository of their merge commit as {@code
  * refs/cache-automerge/} branches. These branches serve:
  *
  * <ul>
  *   <li>as a cache so that the each auto-merge gets computed only once
  *   <li>as base for merge commits on which users can comment
  * </ul>
  *
  * <p>The second point means that these commits are referenced from NoteDb. The consequence of this
  * is that these refs should never be deleted.
  */
 public class AutoMerger {
   @UsedAt(UsedAt.Project.GOOGLE)
   public static boolean cacheAutomerge(Config cfg) {
     return cfg.getBoolean("change", null, "cacheAutomerge", true);
   }

   private final RetryHelper retryHelper;
   private final PersonIdent gerritIdent;
   private final boolean save;

   @Inject
   AutoMerger(
       RetryHelper retryHelper,
       @GerritServerConfig Config cfg,
       @GerritPersonIdent PersonIdent gerritIdent) {
     this.retryHelper = retryHelper;
     save = cacheAutomerge(cfg);
     this.gerritIdent = gerritIdent;
   }

   /**
    * Creates an auto-merge commit of the parents of the given merge commit.
    *
    * <p>In case of an exception the creation of the auto-merge commit is retried a few times. E.g.
    * this allows the operation to succeed if a Git update fails due to a temporary issue.
    *
    * @return auto-merge commit. Headers of the returned RevCommit are parsed.
    */
   public RevCommit merge(
       Repository repo,
       RevWalk rw,
       ObjectInserter ins,
       RevCommit merge,
       ThreeWayMergeStrategy mergeStrategy)
       throws IOException {
     try {
       return retryHelper
           .action(
               ActionType.GIT_UPDATE,
               "createAutoMerge",
               () -> createAutoMergeCommit(repo, rw, ins, merge, mergeStrategy))
           .call();
     } catch (Exception e) {
       Throwables.throwIfUnchecked(e);
       Throwables.throwIfInstanceOf(e, IOException.class);
       throw new IllegalStateException(e);
     }
   }

   /**
    * Creates an auto-merge commit of the parents of the given merge commit.
    *
    * @return auto-merge commit. Headers of the returned RevCommit are parsed.
    */
   private RevCommit createAutoMergeCommit(
       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 = m.merge(merge.getParents());

     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();
     switch (ru.forceUpdate()) {
       case FAST_FORWARD:
       case FORCED:
       case NEW:
       case NO_CHANGE:
         return rw.parseCommit(commitId);
       case LOCK_FAILURE:
         throw new LockFailureException(
             String.format("Failed to create auto-merge of %s", merge.name()), ru);
       case IO_FAILURE:
       case NOT_ATTEMPTED:
       case REJECTED:
       case REJECTED_CURRENT_BRANCH:
       case REJECTED_MISSING_OBJECT:
       case REJECTED_OTHER_REASON:
       case RENAMED:
       default:
         throw new IOException(
             String.format(
                 "Failed to create auto-merge of %s: Cannot write %s (%s)",
                 merge.name(), refName, ru.getResult()));
     }
   }

   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() {}
   }
 }
	// 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.base.Throwables;
	import com.google.gerrit.common.Nullable;
	import com.google.gerrit.common.UsedAt;
	import com.google.gerrit.entities.RefNames;
	import com.google.gerrit.git.LockFailureException;
	import com.google.gerrit.server.GerritPersonIdent;
	import com.google.gerrit.server.config.GerritServerConfig;
	import com.google.gerrit.server.git.InMemoryInserter;
	import com.google.gerrit.server.git.MergeUtil;
	import com.google.gerrit.server.update.RetryHelper;
	import com.google.gerrit.server.update.RetryableAction.ActionType;
	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;

	/**
	* Utility class for creating an auto-merge commit of a merge commit.
	*
	* <p>An auto-merge commit is the result of merging the 2 parents of a merge commit automatically.
	* If there are conflicts the auto-merge commit contains Git conflict markers that indicate these
	* conflicts.
	*
	* <p>Creating auto-merge commits for octopus merges (merge commits with more than 2 parents) is not
	* supported. In this case the auto-merge is created between the first 2 parent commits.
	*
	* <p>All created auto-merge commits are stored in the repository of their merge commit as {@code
	* refs/cache-automerge/} branches. These branches serve:
	*
	* <ul>
	* <li>as a cache so that the each auto-merge gets computed only once
	* <li>as base for merge commits on which users can comment
	* </ul>
	*
	* <p>The second point means that these commits are referenced from NoteDb. The consequence of this
	* is that these refs should never be deleted.
	*/
	public class AutoMerger {
	@UsedAt(UsedAt.Project.GOOGLE)
	public static boolean cacheAutomerge(Config cfg) {
	return cfg.getBoolean("change", null, "cacheAutomerge", true);
	}

	private final RetryHelper retryHelper;
	private final PersonIdent gerritIdent;
	private final boolean save;

	@Inject
	AutoMerger(
	RetryHelper retryHelper,
	@GerritServerConfig Config cfg,
	@GerritPersonIdent PersonIdent gerritIdent) {
	this.retryHelper = retryHelper;
	save = cacheAutomerge(cfg);
	this.gerritIdent = gerritIdent;
	}

	/**
	* Creates an auto-merge commit of the parents of the given merge commit.
	*
	* <p>In case of an exception the creation of the auto-merge commit is retried a few times. E.g.
	* this allows the operation to succeed if a Git update fails due to a temporary issue.
	*
	* @return auto-merge commit. Headers of the returned RevCommit are parsed.
	*/
	public RevCommit merge(
	Repository repo,
	RevWalk rw,
	ObjectInserter ins,
	RevCommit merge,
	ThreeWayMergeStrategy mergeStrategy)
	throws IOException {
	try {
	return retryHelper
	.action(
	ActionType.GIT_UPDATE,
	"createAutoMerge",
	() -> createAutoMergeCommit(repo, rw, ins, merge, mergeStrategy))
	.call();
	} catch (Exception e) {
	Throwables.throwIfUnchecked(e);
	Throwables.throwIfInstanceOf(e, IOException.class);
	throw new IllegalStateException(e);
	}
	}

	/**
	* Creates an auto-merge commit of the parents of the given merge commit.
	*
	* @return auto-merge commit. Headers of the returned RevCommit are parsed.
	*/
	private RevCommit createAutoMergeCommit(
	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 = m.merge(merge.getParents());

	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();
	switch (ru.forceUpdate()) {
	case FAST_FORWARD:
	case FORCED:
	case NEW:
	case NO_CHANGE:
	return rw.parseCommit(commitId);
	case LOCK_FAILURE:
	throw new LockFailureException(
	String.format("Failed to create auto-merge of %s", merge.name()), ru);
	case IO_FAILURE:
	case NOT_ATTEMPTED:
	case REJECTED:
	case REJECTED_CURRENT_BRANCH:
	case REJECTED_MISSING_OBJECT:
	case REJECTED_OTHER_REASON:
	case RENAMED:
	default:
	throw new IOException(
	String.format(
	"Failed to create auto-merge of %s: Cannot write %s (%s)",
	merge.name(), refName, ru.getResult()));
	}
	}

	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() {}
	}
	}