Extend merge support for bare repositories

Optional inCore parameter to Resolver/Strategy will
instruct it to perform all the operations in memory
and avoid modifying working folder even if there is one.

Change-Id: I5b873dead3682f79110f58d7806e43f50bcc5045

org.eclipse.jgit/src/org/eclipse/jgit/merge/MergeStrategy.java

@@ -143,4 +143,18 @@ public abstract class MergeStrategy {
 	 * @return the new merge instance which implements this strategy.
 	 */
 	public abstract Merger newMerger(Repository db);
+
+	/**
+	 * Create a new merge instance.
+	 * 
+	 * @param db
+	 *            repository database the merger will read from, and eventually
+	 *            write results back to.
+	 * @param inCore
+	 *            the merge will happen in memory, working folder will not be
+	 *            modified, in case of a non-trivial merge that requires manual
+	 *            resolution, the merger will fail.
+	 * @return the new merge instance which implements this strategy.
+	 */
+	public abstract Merger newMerger(Repository db, boolean inCore);
 }

org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java

@@ -128,6 +128,8 @@ public class ResolveMerger extends ThreeWayMerger {
 
 	private boolean enterSubtree;
 
+	private boolean inCore;
+
 	private DirCache dircache;
 
 	private WorkingTreeIterator workingTreeIt;
@@ -135,11 +137,24 @@ public class ResolveMerger extends ThreeWayMerger {
 
 	/**
 	 * @param local
+	 * @param inCore
 	 */
-	protected ResolveMerger(Repository local) {
+	protected ResolveMerger(Repository local, boolean inCore) {
 		super(local);
 		commitNames = new String[] { "BASE", "OURS", "THEIRS" };
 		oi = getObjectInserter();
+		this.inCore = inCore;
+
+		if (inCore) {
+			dircache = DirCache.newInCore();
+		}
+	}
+
+	/**
+	 * @param local
+	 */
+	protected ResolveMerger(Repository local) {
+		this(local, false);
 	}
 
 	@Override
@@ -178,12 +193,11 @@ public class ResolveMerger extends ThreeWayMerger {
 					tw.enterSubtree();
 			}
 
+			if (!inCore) {
 				// All content-merges are successfully done. If we can now write the
-			// new
-			// index we are on quite safe ground. Even if the checkout of files
-			// coming from "theirs" fails the user can work around such failures
-			// by
-			// checking out the index again.
+				// new index we are on quite safe ground. Even if the checkout of
+				// files coming from "theirs" fails the user can work around such
+				// failures by checking out the index again.
 				if (!builder.commit()) {
 					cleanUp();
 					throw new IndexWriteException();
@@ -194,6 +208,11 @@ public class ResolveMerger extends ThreeWayMerger {
 				// all files from "theirs" which have been selected to go into the
 				// new index.
 				checkout();
+			} else {
+				builder.finish();
+				builder = null;
+			}
+
 			if (getUnmergedPathes().isEmpty()) {
 				resultTree = dircache.writeTree(oi);
 				return true;
@@ -234,13 +253,19 @@ public class ResolveMerger extends ThreeWayMerger {
 	/**
 	 * Reverts the worktree after an unsuccessful merge. We know that for all
 	 * modified files the old content was in the old index and the index
-	 * contained only stage 0
+	 * contained only stage 0. In case if inCore operation just clear
+	 * the history of modified files.
 	 *
 	 * @throws IOException
 	 * @throws CorruptObjectException
 	 * @throws NoWorkTreeException
 	 */
 	private void cleanUp() throws NoWorkTreeException, CorruptObjectException, IOException {
+		if (inCore) {
+			modifiedFiles.clear();
+			return;
+		}
+
 		DirCache dc = db.readDirCache();
 		ObjectReader or = db.getObjectDatabase().newReader();
 		Iterator<String> mpathsIt=modifiedFiles.iterator();
@@ -391,15 +416,18 @@ public class ResolveMerger extends ThreeWayMerger {
 		}
 
 		if (nonTree(modeO) && nonTree(modeT)) {
-			// We are going to update the worktree. Make sure the worktree is
-			// not modified
+			if (!inCore) {
+				// We are going to update the worktree. Make sure the worktree
+				// is not modified
 				if (work != null
-					&& (!nonTree(work.getEntryRawMode()) || work.isModified(
-							index.getDirCacheEntry(), true, true, db.getFS()))) {
+						&& (!nonTree(work.getEntryRawMode()) || work
+								.isModified(index.getDirCacheEntry(), true,
+										true, db.getFS()))) {
 					failingPathes.put(tw.getPathString(),
 							MergeFailureReason.DIRTY_WORKTREE);
 					return false;
 				}
+			}
 
 			if (!contentMerge(base, ours, theirs)) {
 				unmergedPathes.add(tw.getPathString());
@@ -421,24 +449,41 @@ public class ResolveMerger extends ThreeWayMerger {
 				getRawText(ours.getEntryObjectId(), db),
 				getRawText(theirs.getEntryObjectId(), db));
 
+		File of = null;
+		FileOutputStream fos;
+		if (!inCore) {
 			File workTree = db.getWorkTree();
 			if (workTree == null)
 				// TODO: This should be handled by WorkingTreeIterators which
 				// support write operations
 				throw new UnsupportedOperationException();
 
-		File of = new File(workTree, tw.getPathString());
-		FileOutputStream fos = new FileOutputStream(of);
+			of = new File(workTree, tw.getPathString());
+			fos = new FileOutputStream(of);
 			try {
 				fmt.formatMerge(fos, result, Arrays.asList(commitNames),
 						Constants.CHARACTER_ENCODING);
 			} finally {
 				fos.close();
 			}
+		}
+		else if (!result.containsConflicts()) {
+			// When working inCore, only trivial merges can be handled,
+			// so we generate objects only in conflict free cases
+			of = File.createTempFile("merge_", "_temp", null);
+			fos = new FileOutputStream(of);
+			try {
+				fmt.formatMerge(fos, result, Arrays.asList(commitNames),
+						Constants.CHARACTER_ENCODING);
+			} finally {
+				fos.close();
+			}
+		}
+
 		if (result.containsConflicts()) {
 			// a conflict occured, the file will contain conflict markers
 			// the index will be populated with the three stages and only the
-			// workdir contains the halfways merged content
+			// workdir (if used) contains the halfways merged content
 			add(tw.getRawPath(), base, DirCacheEntry.STAGE_1);
 			add(tw.getRawPath(), ours, DirCacheEntry.STAGE_2);
 			add(tw.getRawPath(), theirs, DirCacheEntry.STAGE_3);
@@ -457,6 +502,8 @@ public class ResolveMerger extends ThreeWayMerger {
 						is));
 			} finally {
 				is.close();
+				if (inCore)
+					of.delete();
 			}
 			builder.add(dce);
 			return true;

org.eclipse.jgit/src/org/eclipse/jgit/merge/StrategyOneSided.java

@@ -84,6 +84,11 @@ public class StrategyOneSided extends MergeStrategy {
 		return new OneSide(db, treeIndex);
 	}
 
+	@Override
+	public Merger newMerger(final Repository db, boolean inCore) {
+		return new OneSide(db, treeIndex);
+	}
+
 	static class OneSide extends Merger {
 		private final int treeIndex;
 

org.eclipse.jgit/src/org/eclipse/jgit/merge/StrategyResolve.java

@@ -49,9 +49,15 @@ import org.eclipse.jgit.lib.Repository;
  * A three-way merge strategy performing a content-merge if necessary
  */
 public class StrategyResolve extends ThreeWayMergeStrategy {
+
 	@Override
 	public ThreeWayMerger newMerger(Repository db) {
-		return new ResolveMerger(db);
+		return new ResolveMerger(db, false);
+	}
+
+	@Override
+	public ThreeWayMerger newMerger(Repository db, boolean inCore) {
+		return new ResolveMerger(db, inCore);
 	}
 
 	@Override

org.eclipse.jgit/src/org/eclipse/jgit/merge/StrategySimpleTwoWayInCore.java

@@ -83,6 +83,12 @@ public class StrategySimpleTwoWayInCore extends ThreeWayMergeStrategy {
 		return new InCoreMerger(db);
 	}
 
+	@Override
+	public ThreeWayMerger newMerger(Repository db, boolean inCore) {
+		// This class is always inCore, so ignore the parameter
+		return newMerger(db);
+	}
+
 	private static class InCoreMerger extends ThreeWayMerger {
 		private static final int T_BASE = 0;
 
@@ -193,4 +199,5 @@ public class StrategySimpleTwoWayInCore extends ThreeWayMergeStrategy {
 			return resultTree;
 		}
 	}
+
 }

org.eclipse.jgit/src/org/eclipse/jgit/merge/ThreeWayMergeStrategy.java

@@ -49,4 +49,7 @@ import org.eclipse.jgit.lib.Repository;
 public abstract class ThreeWayMergeStrategy extends MergeStrategy {
 	@Override
 	public abstract ThreeWayMerger newMerger(Repository db);
+
+	@Override
+	public abstract ThreeWayMerger newMerger(Repository db, boolean inCore);
 }

org.eclipse.jgit/src/org/eclipse/jgit/merge/ThreeWayMerger.java

@@ -66,6 +66,18 @@ public abstract class ThreeWayMerger extends Merger {
 		super(local);
 	}
 
+	/**
+	 * Create a new merge instance for a repository.
+	 *
+	 * @param local
+	 *            the repository this merger will read and write data on.
+	 * @param inCore
+	 *            perform the merge in core with no working folder involved
+	 */
+	protected ThreeWayMerger(final Repository local, boolean inCore) {
+		this(local);
+	}
+
 	/**
 	 * Set the common ancestor tree.
 	 *