CommitCommand: Don't allow amending on initial commit

Change-Id: I27b13510eb6756da21d0d359d76031da4a875e28

org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CommitCommandTest.java

@@ -50,6 +50,7 @@ import static org.junit.Assert.assertTrue;
 import java.io.File;
 import java.util.List;
 
+import org.eclipse.jgit.api.errors.WrongRepositoryStateException;
 import org.eclipse.jgit.diff.DiffEntry;
 import org.eclipse.jgit.dircache.DirCache;
 import org.eclipse.jgit.lib.ConfigConstants;
@@ -420,4 +421,10 @@ public class CommitCommandTest extends RepositoryTestCase {
 		assertEquals("commit: Squashed commit of the following:", db
 				.getReflogReader(db.getBranch()).getLastEntry().getComment());
 	}
+
+	@Test(expected = WrongRepositoryStateException.class)
+	public void commitAmendOnInitialShouldFail() throws Exception {
+		Git git = new Git(db);
+		git.commit().setAmend(true).setMessage("initial commit").call();
+	}
 }

org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties

@@ -86,6 +86,7 @@ commandWasCalledInTheWrongState=Command {0} was called in the wrong state
 commitAlreadyExists=exists {0}
 commitMessageNotSpecified=commit message not specified
 commitOnRepoWithoutHEADCurrentlyNotSupported=Commit on repo without HEAD currently not supported
+commitAmendOnInitialNotPossible=Amending is not possible on initial commit.
 compressingObjects=Compressing objects
 connectionFailed=connection failed
 connectionTimeOut=Connection time out: {0}

org.eclipse.jgit/src/org/eclipse/jgit/api/CommitCommand.java

@@ -176,6 +176,10 @@ public class CommitCommand extends GitCommand<RevCommit> {
 
 			// determine the current HEAD and the commit it is referring to
 			ObjectId headId = repo.resolve(Constants.HEAD + "^{commit}");
+			if (headId == null && amend)
+				throw new WrongRepositoryStateException(
+						JGitText.get().commitAmendOnInitialNotPossible);
+
 			if (headId != null)
 				if (amend) {
 					RevCommit previousCommit = new RevWalk(repo)

org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java

@@ -146,6 +146,7 @@ public class JGitText extends TranslationBundle {
 	/***/ public String commitAlreadyExists;
 	/***/ public String commitMessageNotSpecified;
 	/***/ public String commitOnRepoWithoutHEADCurrentlyNotSupported;
+	/***/ public String commitAmendOnInitialNotPossible;
 	/***/ public String compressingObjects;
 	/***/ public String connectionFailed;
 	/***/ public String connectionTimeOut;