Add command support for applying a stashed commit

Applies the changes in a stashed commit to the local working
directory and index

Bug: 309355
Change-Id: I9fd5ede8affc7f0060ffa7c5cec34573b6fa2b1b
Signed-off-by: Chris Aniszczyk <zx@twitter.com>

5 files changed, 567 insertions, 10 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/StashApplyCommandTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/StashApplyCommandTest.java
new file mode 100644
index 0000000000..0b17972223
--- /dev/null
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/api/StashApplyCommandTest.java
@@ -0,0 +1,346 @@
+/*
+ * Copyright (C) 2012, GitHub Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.api;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+import java.io.File;
+
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.RepositoryTestCase;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.util.FileUtils;
+import org.junit.Before;
+import org.junit.Test;
+
+/**
+ * Unit tests of {@link StashApplyCommand}
+ */
+public class StashApplyCommandTest extends RepositoryTestCase {
+
+	private static final String PATH = "file.txt";
+
+	private RevCommit head;
+
+	private Git git;
+
+	private File committedFile;
+
+	@Before
+	public void setUp() throws Exception {
+		super.setUp();
+		git = Git.wrap(db);
+		committedFile = writeTrashFile(PATH, "content");
+		git.add().addFilepattern(PATH).call();
+		head = git.commit().setMessage("add file").call();
+		assertNotNull(head);
+	}
+
+	@Test
+	public void workingDirectoryDelete() throws Exception {
+		deleteTrashFile(PATH);
+		assertFalse(committedFile.exists());
+		RevCommit stashed = git.stashCreate().call();
+		assertNotNull(stashed);
+		assertEquals("content", read(committedFile));
+
+		ObjectId unstashed = git.stashApply().call();
+		assertEquals(stashed, unstashed);
+		assertFalse(committedFile.exists());
+
+		Status status = git.status().call();
+		assertTrue(status.getAdded().isEmpty());
+		assertTrue(status.getChanged().isEmpty());
+		assertTrue(status.getConflicting().isEmpty());
+		assertTrue(status.getModified().isEmpty());
+		assertTrue(status.getUntracked().isEmpty());
+		assertTrue(status.getRemoved().isEmpty());
+
+		assertEquals(1, status.getMissing().size());
+		assertTrue(status.getMissing().contains(PATH));
+	}
+
+	@Test
+	public void indexAdd() throws Exception {
+		String addedPath = "file2.txt";
+		File addedFile = writeTrashFile(addedPath, "content2");
+		git.add().addFilepattern(addedPath).call();
+
+		RevCommit stashed = Git.wrap(db).stashCreate().call();
+		assertNotNull(stashed);
+		assertFalse(addedFile.exists());
+
+		ObjectId unstashed = git.stashApply().call();
+		assertEquals(stashed, unstashed);
+		assertTrue(addedFile.exists());
+		assertEquals("content2", read(addedFile));
+
+		Status status = git.status().call();
+		assertTrue(status.getChanged().isEmpty());
+		assertTrue(status.getConflicting().isEmpty());
+		assertTrue(status.getMissing().isEmpty());
+		assertTrue(status.getModified().isEmpty());
+		assertTrue(status.getRemoved().isEmpty());
+		assertTrue(status.getUntracked().isEmpty());
+
+		assertEquals(1, status.getAdded().size());
+		assertTrue(status.getAdded().contains(addedPath));
+	}
+
+	@Test
+	public void indexDelete() throws Exception {
+		git.rm().addFilepattern("file.txt").call();
+
+		RevCommit stashed = Git.wrap(db).stashCreate().call();
+		assertNotNull(stashed);
+		assertEquals("content", read(committedFile));
+
+		ObjectId unstashed = git.stashApply().call();
+		assertEquals(stashed, unstashed);
+		assertFalse(committedFile.exists());
+
+		Status status = git.status().call();
+		assertTrue(status.getAdded().isEmpty());
+		assertTrue(status.getChanged().isEmpty());
+		assertTrue(status.getConflicting().isEmpty());
+		assertTrue(status.getModified().isEmpty());
+		assertTrue(status.getMissing().isEmpty());
+		assertTrue(status.getUntracked().isEmpty());
+
+		assertEquals(1, status.getRemoved().size());
+		assertTrue(status.getRemoved().contains(PATH));
+	}
+
+	@Test
+	public void workingDirectoryModify() throws Exception {
+		writeTrashFile("file.txt", "content2");
+
+		RevCommit stashed = Git.wrap(db).stashCreate().call();
+		assertNotNull(stashed);
+		assertEquals("content", read(committedFile));
+
+		ObjectId unstashed = git.stashApply().call();
+		assertEquals(stashed, unstashed);
+		assertEquals("content2", read(committedFile));
+
+		Status status = git.status().call();
+		assertTrue(status.getAdded().isEmpty());
+		assertTrue(status.getChanged().isEmpty());
+		assertTrue(status.getConflicting().isEmpty());
+		assertTrue(status.getMissing().isEmpty());
+		assertTrue(status.getRemoved().isEmpty());
+		assertTrue(status.getUntracked().isEmpty());
+
+		assertEquals(1, status.getModified().size());
+		assertTrue(status.getModified().contains(PATH));
+	}
+
+	@Test
+	public void workingDirectoryModifyInSubfolder() throws Exception {
+		String path = "d1/d2/f.txt";
+		File subfolderFile = writeTrashFile(path, "content");
+		git.add().addFilepattern(path).call();
+		head = git.commit().setMessage("add file").call();
+
+		writeTrashFile(path, "content2");
+
+		RevCommit stashed = Git.wrap(db).stashCreate().call();
+		assertNotNull(stashed);
+		assertEquals("content", read(subfolderFile));
+
+		ObjectId unstashed = git.stashApply().call();
+		assertEquals(stashed, unstashed);
+		assertEquals("content2", read(subfolderFile));
+
+		Status status = git.status().call();
+		assertTrue(status.getAdded().isEmpty());
+		assertTrue(status.getChanged().isEmpty());
+		assertTrue(status.getConflicting().isEmpty());
+		assertTrue(status.getMissing().isEmpty());
+		assertTrue(status.getRemoved().isEmpty());
+		assertTrue(status.getUntracked().isEmpty());
+
+		assertEquals(1, status.getModified().size());
+		assertTrue(status.getModified().contains(path));
+	}
+
+	@Test
+	public void workingDirectoryModifyIndexChanged() throws Exception {
+		writeTrashFile("file.txt", "content2");
+		git.add().addFilepattern("file.txt").call();
+		writeTrashFile("file.txt", "content3");
+
+		RevCommit stashed = Git.wrap(db).stashCreate().call();
+		assertNotNull(stashed);
+		assertEquals("content", read(committedFile));
+
+		ObjectId unstashed = git.stashApply().call();
+		assertEquals(stashed, unstashed);
+		assertEquals("content3", read(committedFile));
+
+		Status status = git.status().call();
+		assertTrue(status.getAdded().isEmpty());
+		assertTrue(status.getConflicting().isEmpty());
+		assertTrue(status.getMissing().isEmpty());
+		assertTrue(status.getRemoved().isEmpty());
+		assertTrue(status.getUntracked().isEmpty());
+
+		assertEquals(1, status.getChanged().size());
+		assertTrue(status.getChanged().contains(PATH));
+		assertEquals(1, status.getModified().size());
+		assertTrue(status.getModified().contains(PATH));
+	}
+
+	@Test
+	public void workingDirectoryCleanIndexModify() throws Exception {
+		writeTrashFile("file.txt", "content2");
+		git.add().addFilepattern("file.txt").call();
+		writeTrashFile("file.txt", "content");
+
+		RevCommit stashed = Git.wrap(db).stashCreate().call();
+		assertNotNull(stashed);
+		assertEquals("content", read(committedFile));
+
+		ObjectId unstashed = git.stashApply().call();
+		assertEquals(stashed, unstashed);
+		assertEquals("content2", read(committedFile));
+
+		Status status = git.status().call();
+		assertTrue(status.getAdded().isEmpty());
+		assertTrue(status.getConflicting().isEmpty());
+		assertTrue(status.getMissing().isEmpty());
+		assertTrue(status.getModified().isEmpty());
+		assertTrue(status.getRemoved().isEmpty());
+		assertTrue(status.getUntracked().isEmpty());
+
+		assertEquals(1, status.getChanged().size());
+		assertTrue(status.getChanged().contains(PATH));
+	}
+
+	@Test
+	public void workingDirectoryDeleteIndexAdd() throws Exception {
+		String path = "file2.txt";
+		File added = writeTrashFile(path, "content2");
+		assertTrue(added.exists());
+		git.add().addFilepattern(path).call();
+		FileUtils.delete(added);
+		assertFalse(added.exists());
+
+		RevCommit stashed = Git.wrap(db).stashCreate().call();
+		assertNotNull(stashed);
+		assertFalse(added.exists());
+
+		ObjectId unstashed = git.stashApply().call();
+		assertEquals(stashed, unstashed);
+		assertEquals("content2", read(added));
+
+		Status status = git.status().call();
+		assertTrue(status.getChanged().isEmpty());
+		assertTrue(status.getConflicting().isEmpty());
+		assertTrue(status.getMissing().isEmpty());
+		assertTrue(status.getModified().isEmpty());
+		assertTrue(status.getRemoved().isEmpty());
+		assertTrue(status.getUntracked().isEmpty());
+
+		assertEquals(1, status.getAdded().size());
+		assertTrue(status.getAdded().contains(path));
+	}
+
+	@Test
+	public void workingDirectoryDeleteIndexEdit() throws Exception {
+		writeTrashFile(PATH, "content2");
+		git.add().addFilepattern(PATH).call();
+		FileUtils.delete(committedFile);
+		assertFalse(committedFile.exists());
+
+		RevCommit stashed = Git.wrap(db).stashCreate().call();
+		assertNotNull(stashed);
+		assertEquals("content", read(committedFile));
+
+		ObjectId unstashed = git.stashApply().call();
+		assertEquals(stashed, unstashed);
+		assertFalse(committedFile.exists());
+
+		Status status = git.status().call();
+		assertTrue(status.getAdded().isEmpty());
+		assertTrue(status.getChanged().isEmpty());
+		assertTrue(status.getConflicting().isEmpty());
+		assertTrue(status.getMissing().isEmpty());
+		assertTrue(status.getModified().isEmpty());
+		assertTrue(status.getUntracked().isEmpty());
+
+		assertEquals(1, status.getRemoved().size());
+		assertTrue(status.getRemoved().contains(PATH));
+	}
+
+	@Test
+	public void multipleEdits() throws Exception {
+		String addedPath = "file2.txt";
+		git.rm().addFilepattern(PATH).call();
+		File addedFile = writeTrashFile(addedPath, "content2");
+		git.add().addFilepattern(addedPath).call();
+
+		RevCommit stashed = Git.wrap(db).stashCreate().call();
+		assertNotNull(stashed);
+		assertTrue(committedFile.exists());
+		assertFalse(addedFile.exists());
+
+		ObjectId unstashed = git.stashApply().call();
+		assertEquals(stashed, unstashed);
+
+		Status status = git.status().call();
+		assertTrue(status.getChanged().isEmpty());
+		assertTrue(status.getConflicting().isEmpty());
+		assertTrue(status.getMissing().isEmpty());
+		assertTrue(status.getModified().isEmpty());
+		assertTrue(status.getUntracked().isEmpty());
+
+		assertEquals(1, status.getRemoved().size());
+		assertTrue(status.getRemoved().contains(PATH));
+		assertEquals(1, status.getAdded().size());
+		assertTrue(status.getAdded().contains(addedPath));
+	}
+}
diff --git a/org.eclipse.jgit/resources/org/eclipse/jgit/JGitText.properties b/org.eclipse.jgit/resources/org/eclipse/jgit/JGitText.properties
index 5a916f5a43..b796c736ce 100644
--- a/org.eclipse.jgit/resources/org/eclipse/jgit/JGitText.properties
+++ b/org.eclipse.jgit/resources/org/eclipse/jgit/JGitText.properties
@@ -423,7 +423,11 @@ sourceRefDoesntResolveToAnyObject=Source ref {0} doesn't resolve to any object.
 sourceRefNotSpecifiedForRefspec=Source ref not specified for refspec: {0}
 staleRevFlagsOn=Stale RevFlags on {0}
 startingReadStageWithoutWrittenRequestDataPendingIsNotSupported=Starting read stage without written request data pending is not supported
+stashApplyFailed=Applying stashed changes did not successfully complete
+stashApplyOnUnsafeRepository=Cannot apply stashed commit on a repository with state: {0}
+stashCommitMissingTwoParents=Stashed commit ''{0}'' does not have two parent commits
 stashFailed=Stashing local changes did not successfully complete
+stashResolveFailed=Reference ''{0}'' does not resolve to stashed commit
 statelessRPCRequiresOptionToBeEnabled=stateless RPC requires {0} to be enabled
 submoduleExists=Submodule ''{0}'' already exists in the index
 submoduleParentRemoteUrlInvalid=Cannot remove segment from remote url ''{0}''
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/JGitText.java b/org.eclipse.jgit/src/org/eclipse/jgit/JGitText.java
index 0276f68612..a75bf1fdd8 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/JGitText.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/JGitText.java
@@ -483,7 +483,11 @@ public class JGitText extends TranslationBundle {
 	/***/ public String sourceRefNotSpecifiedForRefspec;
 	/***/ public String staleRevFlagsOn;
 	/***/ public String startingReadStageWithoutWrittenRequestDataPendingIsNotSupported;
+	/***/ public String stashApplyFailed;
+	/***/ public String stashApplyOnUnsafeRepository;
+	/***/ public String stashCommitMissingTwoParents;
 	/***/ public String stashFailed;
+	/***/ public String stashResolveFailed;
 	/***/ public String statelessRPCRequiresOptionToBeEnabled;
 	/***/ public String submoduleExists;
 	/***/ public String submodulesNotSupported;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
index 0c5b56a6cc..597ce99b15 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
@@ -54,7 +54,8 @@ import org.eclipse.jgit.util.FS;
 /**
  * Offers a "GitPorcelain"-like API to interact with a git repository.
  * <p>
- * The GitPorcelain commands are described in the <a href="http://www.kernel.org/pub/software/scm/git/docs/git.html#_high_level_commands_porcelain"
+ * The GitPorcelain commands are described in the <a href=
+ * "http://www.kernel.org/pub/software/scm/git/docs/git.html#_high_level_commands_porcelain"
  * >Git Documentation</a>.
  * <p>
  * This class only offers methods to construct so-called command classes. Each
@@ -109,9 +110,7 @@ public class Git {
 		RepositoryCache.FileKey key;
 
 		key = RepositoryCache.FileKey.lenient(dir, fs);
-		return wrap(new RepositoryBuilder()
-				.setFS(fs)
-				.setGitDir(key.getFile())
+		return wrap(new RepositoryBuilder().setFS(fs).setGitDir(key.getFile())
 				.setMustExist(true).build());
 	}
 
@@ -266,8 +265,8 @@ public class Git {
 	 * @see <a
 	 *      href="http://www.kernel.org/pub/software/scm/git/docs/git-add.html"
 	 *      >Git documentation about Add</a>
-	 * @return a {@link AddCommand} used to collect all optional parameters
-	 *         and to finally execute the {@code Add} command
+	 * @return a {@link AddCommand} used to collect all optional parameters and
+	 *         to finally execute the {@code Add} command
 	 */
 	public AddCommand add() {
 		return new AddCommand(repo);
@@ -279,8 +278,8 @@ public class Git {
 	 * @see <a
 	 *      href="http://www.kernel.org/pub/software/scm/git/docs/git-tag.html"
 	 *      >Git documentation about Tag</a>
-	 * @return a {@link TagCommand} used to collect all optional parameters
-	 *         and to finally execute the {@code Tag} command
+	 * @return a {@link TagCommand} used to collect all optional parameters and
+	 *         to finally execute the {@code Tag} command
 	 */
 	public TagCommand tag() {
 		return new TagCommand(repo);
@@ -331,8 +330,8 @@ public class Git {
 	 * @see <a
 	 *      href="http://www.kernel.org/pub/software/scm/git/docs/git-revert.html"
 	 *      >Git documentation about reverting changes</a>
-	 * @return a {@link RevertCommand} used to collect all optional
-	 *         parameters and to finally execute the {@code cherry-pick} command
+	 * @return a {@link RevertCommand} used to collect all optional parameters
+	 *         and to finally execute the {@code cherry-pick} command
 	 */
 	public RevertCommand revert() {
 		return new RevertCommand(repo);
@@ -583,6 +582,15 @@ public class Git {
 	}
 
 	/**
+	 * Returns a command object used to apply a stashed commit
+	 *
+	 * @return a {@link StashApplyCommand}
+	 */
+	public StashApplyCommand stashApply() {
+		return new StashApplyCommand(repo);
+	}
+
+	/**
 	 * @return the git repository this class is interacting with
 	 */
 	public Repository getRepository() {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/StashApplyCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/StashApplyCommand.java
new file mode 100644
index 0000000000..dcb04953ff
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/StashApplyCommand.java
@@ -0,0 +1,195 @@
+/*
+ * Copyright (C) 2012, GitHub Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.api;
+
+import java.io.File;
+import java.io.IOException;
+import java.text.MessageFormat;
+
+import org.eclipse.jgit.JGitText;
+import org.eclipse.jgit.api.errors.GitAPIException;
+import org.eclipse.jgit.api.errors.InvalidRefNameException;
+import org.eclipse.jgit.api.errors.JGitInternalException;
+import org.eclipse.jgit.api.errors.WrongRepositoryStateException;
+import org.eclipse.jgit.dircache.DirCache;
+import org.eclipse.jgit.dircache.DirCacheCheckout;
+import org.eclipse.jgit.dircache.DirCacheEditor;
+import org.eclipse.jgit.dircache.DirCacheEditor.DeletePath;
+import org.eclipse.jgit.dircache.DirCacheEntry;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.lib.RepositoryState;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevTree;
+import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.treewalk.AbstractTreeIterator;
+import org.eclipse.jgit.treewalk.FileTreeIterator;
+import org.eclipse.jgit.treewalk.TreeWalk;
+import org.eclipse.jgit.treewalk.filter.TreeFilter;
+import org.eclipse.jgit.util.FileUtils;
+
+/**
+ * Command class to apply a stashed commit.
+ *
+ * @see <a href="http://www.kernel.org/pub/software/scm/git/docs/git-stash.html"
+ *      >Git documentation about Stash</a>
+ */
+public class StashApplyCommand extends GitCommand<ObjectId> {
+
+	private static final String DEFAULT_REF = Constants.STASH + "@{0}";
+
+	private String stashRef;
+
+	/**
+	 * Create command to apply the changes of a stashed commit
+	 *
+	 * @param repo
+	 */
+	public StashApplyCommand(final Repository repo) {
+		super(repo);
+	}
+
+	/**
+	 * Set the stash reference to apply
+	 * <p>
+	 * This will default to apply the latest stashed commit (stash@{0}) if
+	 * unspecified
+	 *
+	 * @param stashRef
+	 * @return {@code this}
+	 */
+	public StashApplyCommand setStashRef(final String stashRef) {
+		this.stashRef = stashRef;
+		return this;
+	}
+
+	/**
+	 * Apply the changes in a stashed commit to the working directory and index
+	 *
+	 * @return id of stashed commit that was applied
+	 */
+	public ObjectId call() throws GitAPIException, JGitInternalException {
+		checkCallable();
+
+		if (repo.getRepositoryState() != RepositoryState.SAFE)
+			throw new WrongRepositoryStateException(MessageFormat.format(
+					JGitText.get().stashApplyOnUnsafeRepository,
+					repo.getRepositoryState()));
+
+		final String revision = stashRef != null ? stashRef : DEFAULT_REF;
+		final ObjectId stashId;
+		try {
+			stashId = repo.resolve(revision);
+		} catch (IOException e) {
+			throw new JGitInternalException(JGitText.get().stashApplyFailed, e);
+		}
+		if (stashId == null)
+			throw new InvalidRefNameException(MessageFormat.format(
+					JGitText.get().stashResolveFailed, revision));
+
+		ObjectReader reader = repo.newObjectReader();
+		try {
+			RevWalk revWalk = new RevWalk(reader);
+			RevCommit wtCommit = revWalk.parseCommit(stashId);
+			if (wtCommit.getParentCount() != 2)
+				throw new JGitInternalException(MessageFormat.format(
+						JGitText.get().stashCommitMissingTwoParents,
+						stashId.name()));
+
+			// Apply index changes
+			RevTree indexTree = revWalk.parseCommit(wtCommit.getParent(1))
+					.getTree();
+			DirCacheCheckout dco = new DirCacheCheckout(repo,
+					repo.lockDirCache(), indexTree, new FileTreeIterator(repo));
+			dco.setFailOnConflict(true);
+			dco.checkout();
+
+			// Apply working directory changes
+			RevTree headTree = revWalk.parseCommit(wtCommit.getParent(0))
+					.getTree();
+			DirCache cache = repo.lockDirCache();
+			DirCacheEditor editor = cache.editor();
+			try {
+				TreeWalk treeWalk = new TreeWalk(reader);
+				treeWalk.setRecursive(true);
+				treeWalk.addTree(headTree);
+				treeWalk.addTree(indexTree);
+				treeWalk.addTree(wtCommit.getTree());
+				treeWalk.setFilter(TreeFilter.ANY_DIFF);
+				File workingTree = repo.getWorkTree();
+				while (treeWalk.next()) {
+					String path = treeWalk.getPathString();
+					File file = new File(workingTree, path);
+					AbstractTreeIterator headIter = treeWalk.getTree(0,
+							AbstractTreeIterator.class);
+					AbstractTreeIterator indexIter = treeWalk.getTree(1,
+							AbstractTreeIterator.class);
+					AbstractTreeIterator wtIter = treeWalk.getTree(2,
+							AbstractTreeIterator.class);
+					if (wtIter != null) {
+						DirCacheEntry entry = new DirCacheEntry(
+								treeWalk.getRawPath());
+						entry.setObjectId(wtIter.getEntryObjectId());
+						DirCacheCheckout.checkoutEntry(repo, file, entry);
+					} else {
+						if (indexIter != null && headIter != null
+								&& !indexIter.idEqual(headIter))
+							editor.add(new DeletePath(path));
+						FileUtils.delete(file, FileUtils.RETRY
+								| FileUtils.SKIP_MISSING);
+					}
+				}
+			} finally {
+				editor.commit();
+				cache.unlock();
+			}
+		} catch (IOException e) {
+			throw new JGitInternalException(JGitText.get().stashApplyFailed, e);
+		} finally {
+			reader.release();
+		}
+		return stashId;
+	}
+}