Add option to allow empty commits to CommitCommand

CommitCommand should allow to specify whether empty commits (commits
having the same tree as the sole predecessor commit) are allowed or not.
Similar to native git's "--allow-empty" flag.

The defaults differ between JGit and native git even after this change.
When not specifying paths then by default JGit allows to create empty
commits while native git does not. It would be API breaking to change
this now.

Bug: 460301
Change-Id: I88feb0c3ffb2c686b1d0594e669729b065cda4cb
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/CommitCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/CommitCommand.java
index 4f9a5a3178..b5057ad282 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/CommitCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/CommitCommand.java
@@ -53,6 +53,7 @@ import java.util.List;
 
 import org.eclipse.jgit.api.errors.AbortedByHookException;
 import org.eclipse.jgit.api.errors.ConcurrentRefUpdateException;
+import org.eclipse.jgit.api.errors.EmtpyCommitException;
 import org.eclipse.jgit.api.errors.GitAPIException;
 import org.eclipse.jgit.api.errors.JGitInternalException;
 import org.eclipse.jgit.api.errors.NoFilepatternException;
@@ -130,6 +131,8 @@ public class CommitCommand extends GitCommand<RevCommit> {
 
 	private PrintStream hookOutRedirect;
 
+	private Boolean allowEmpty;
+
 	/**
 	 * @param repo
 	 */
@@ -231,6 +234,16 @@ public class CommitCommand extends GitCommand<RevCommit> {
 				if (insertChangeId)
 					insertChangeId(indexTreeId);
 
+				// Check for empty commits
+				if (headId != null && !allowEmpty.booleanValue()) {
+					RevCommit headCommit = rw.parseCommit(headId);
+					headCommit.getTree();
+					if (indexTreeId.equals(headCommit.getTree())) {
+						throw new EmtpyCommitException(
+								JGitText.get().emptyCommit);
+					}
+				}
+
 				// Create a Commit object, populate it and write it
 				CommitBuilder commit = new CommitBuilder();
 				commit.setCommitter(committer);
@@ -457,6 +470,8 @@ public class CommitCommand extends GitCommand<RevCommit> {
 
 		// there must be at least one change
 		if (emptyCommit)
+			// Would like to throw a EmptyCommitException. But this would break the API
+			// TODO(ch): Change this in the next release
 			throw new JGitInternalException(JGitText.get().emptyCommit);
 
 		// update index
@@ -510,6 +525,12 @@ public class CommitCommand extends GitCommand<RevCommit> {
 			committer = new PersonIdent(repo);
 		if (author == null && !amend)
 			author = committer;
+		if (allowEmpty == null)
+			// JGit allows empty commits by default. Only when pathes are
+			// specified the commit should not be empty. This behaviour differs
+			// from native git but can only be adapted in the next release.
+			// TODO(ch) align the defaults with native git
+			allowEmpty = (only.isEmpty()) ? Boolean.TRUE : Boolean.FALSE;
 
 		// when doing a merge commit parse MERGE_HEAD and MERGE_MSG files
 		if (state == RepositoryState.MERGING_RESOLVED
@@ -579,6 +600,27 @@ public class CommitCommand extends GitCommand<RevCommit> {
 	}
 
 	/**
+	 * @param allowEmpty
+	 *            whether it should be allowed to create a commit which has the
+	 *            same tree as it's sole predecessor (a commit which doesn't
+	 *            change anything). By default when creating standard commits
+	 *            (without specifying paths) JGit allows to create such commits.
+	 *            When this flag is set to false an attempt to create an "empty"
+	 *            standard commit will lead to an EmptyCommitException.
+	 *            <p>
+	 *            By default when creating a commit containing only specified
+	 *            paths an attempt to create an empty commit leads to a
+	 *            {@link JGitInternalException}. By setting this flag to
+	 *            <code>true</code> this exception will not be thrown.
+	 * @return {@code this}
+	 * @since 4.2
+	 */
+	public CommitCommand setAllowEmpty(boolean allowEmpty) {
+		this.allowEmpty = Boolean.valueOf(allowEmpty);
+		return this;
+	}
+
+	/**
 	 * @return the commit message used for the <code>commit</code>
 	 */
 	public String getMessage() {