Revert "CommitBuilder should check for duplicate parents"

This reverts commit 6bc48cdc62.

Until git v1.7.10.2~29^2~1 (builtin/merge.c: reduce parents early,
2012-04-17), C git merge would make merge commits with duplicate parents
when asked to with a series of commands like the following:

  git checkout origin/master
  git merge --no-ff origin/master

Nowadays "git merge" removes redundant parents more aggressively
(whenever one parent is an ancestor of another and not just when
duplicates exist) but merges with duplicate parents are still permitted
and can be created with git fast-import or git commit-tree and history
viewers need to be able to cope with them.

CommitBuilder is an interface analagous to commit-tree, so it should
allow duplicate parents.  (That said, an option to automatically remove
redundant parents would be useful.)

Reported-by: Dave Borowitz <dborowitz@google.com>
Change-Id: Ia682238397eb1de8541802210fa875fdd50f62f0
Signed-off-by: Jonathan Nieder <jrn@google.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/SimpleMergeTest.java

 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.fail;
 
 import java.io.IOException;
-import java.util.Arrays;
-import java.util.List;
 
 import org.eclipse.jgit.dircache.DirCache;
 import org.eclipse.jgit.dircache.DirCacheBuilder;
-import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.CommitBuilder;
 import org.eclipse.jgit.lib.FileMode;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectInserter;
 import org.eclipse.jgit.lib.PersonIdent;
-import org.eclipse.jgit.revwalk.RevCommit;
-import org.eclipse.jgit.revwalk.RevWalk;
 import org.eclipse.jgit.test.resources.SampleDataRepositoryTestCase;
 import org.eclipse.jgit.treewalk.TreeWalk;
 import org.junit.Test;
 		assertEquals("02ba32d3649e510002c21651936b7077aa75ffa9",ourMerger.getResultTreeId().name());
 	}
 
-	@Test
-	public void testDuplicateParents() throws Exception {
-		ObjectId commitId;
-		RevCommit newCommit;
-		final ObjectInserter ow = db.newObjectInserter();
-		RevWalk rw = new RevWalk(db);
-		ObjectId parentA = db.resolve("a");
-		ObjectId parentB = db.resolve("b");
-		ObjectId[] parentIds_AA = new ObjectId[] { parentA, parentA };
-		ObjectId[] parentIds_AB = new ObjectId[] { parentA, parentB };
-		ObjectId[] parentIds_BA = new ObjectId[] { parentB, parentA };
-		ObjectId[] parentIds_BBAB = new ObjectId[] { parentB, parentB, parentA,
-				parentB };
-
-		try {
-			commitId = commit(ow, db.readDirCache(), parentA, parentA);
-			fail("an expected exception did not occur");
-		} catch (IllegalArgumentException e) {
-			//
-		}
-
-		commitId = commit(ow, db.readDirCache(), parentA, parentB);
-		newCommit = rw.parseCommit(commitId);
-		assertEquals(2, newCommit.getParentCount());
-
-		commitId = commit(ow, db.readDirCache(), parentB, parentA);
-		newCommit = rw.parseCommit(commitId);
-		assertEquals(2, newCommit.getParentCount());
-
-		try {
-			commitId = commit(ow, db.readDirCache(), parentIds_AA);
-			fail("an expected exception did not occur");
-		} catch (IllegalArgumentException e) {
-			//
-		}
-
-		commitId = commit(ow, db.readDirCache(), parentIds_AB);
-		newCommit = rw.parseCommit(commitId);
-		assertEquals(2, newCommit.getParentCount());
-
-		commitId = commit(ow, db.readDirCache(), parentIds_BA);
-		newCommit = rw.parseCommit(commitId);
-		assertEquals(2, newCommit.getParentCount());
-
-		try {
-			commitId = commit(ow, db.readDirCache(), parentIds_BBAB);
-			fail("an expected exception did not occur");
-		} catch (IllegalArgumentException e) {
-			//
-		}
-
-		try {
-			commitId = commit(ow, db.readDirCache(),
-					Arrays.asList(parentIds_AA));
-			fail("an expected exception did not occur");
-		} catch (IllegalArgumentException e) {
-			//
-		}
-
-		commitId = commit(ow, db.readDirCache(), parentIds_AB);
-		newCommit = rw.parseCommit(commitId);
-		assertEquals(2, newCommit.getParentCount());
-
-		commitId = commit(ow, db.readDirCache(), parentIds_BA);
-		newCommit = rw.parseCommit(commitId);
-		assertEquals(2, newCommit.getParentCount());
-
-		try {
-			commitId = commit(ow, db.readDirCache(), parentIds_BBAB);
-			fail("an expected exception did not occur");
-		} catch (IllegalArgumentException e) {
-			//
-		}
-	}
-
 	@Test
 	public void testTrivialTwoWay_disjointhistories() throws IOException {
 		Merger ourMerger = MergeStrategy.SIMPLE_TWO_WAY_IN_CORE.newMerger(db);
 		odi.flush();
 		return id;
 	}
-
-	private ObjectId commit(final ObjectInserter odi, final DirCache treeB,
-			final AnyObjectId parentId1, final AnyObjectId parentId2)
-			throws Exception {
-		final CommitBuilder c = new CommitBuilder();
-		c.setTreeId(treeB.writeTree(odi));
-		c.setAuthor(new PersonIdent("A U Thor", "a.u.thor", 1L, 0));
-		c.setCommitter(c.getAuthor());
-		c.setParentIds(parentId1, parentId2);
-		c.setMessage("Tree " + c.getTreeId().name());
-		ObjectId id = odi.insert(c);
-		odi.flush();
-		return id;
-	}
-
-	private ObjectId commit(final ObjectInserter odi, final DirCache treeB,
-			List<ObjectId> parents) throws Exception {
-		final CommitBuilder c = new CommitBuilder();
-		c.setTreeId(treeB.writeTree(odi));
-		c.setAuthor(new PersonIdent("A U Thor", "a.u.thor", 1L, 0));
-		c.setCommitter(c.getAuthor());
-		c.setParentIds(parents);
-		c.setMessage("Tree " + c.getTreeId().name());
-		ObjectId id = odi.insert(c);
-		odi.flush();
-		return id;
-	}
 }

org.eclipse.jgit.test/tst/org/eclipse/jgit/revplot/PlotCommitListTest.java

 		test.noMoreCommits();
 	}
 
+	// test a history where a merge commit has two time the same parent
+	@Test
+	public void testDuplicateParents() throws Exception {
+		final RevCommit m1 = commit();
+		final RevCommit m2 = commit(m1);
+		final RevCommit m3 = commit(m2, m2);
+
+		final RevCommit s1 = commit(m2);
+		final RevCommit s2 = commit(s1);
+
+		PlotWalk pw = new PlotWalk(db);
+		pw.markStart(pw.lookupCommit(m3));
+		pw.markStart(pw.lookupCommit(s2));
+		PlotCommitList<PlotLane> pcl = new PlotCommitList<PlotLane>();
+		pcl.source(pw);
+		pcl.fillTo(Integer.MAX_VALUE);
+
+		CommitListAssert test = new CommitListAssert(pcl);
+		test.commit(s2).nrOfPassingLanes(0);
+		test.commit(s1).nrOfPassingLanes(0);
+		test.commit(m3).nrOfPassingLanes(1);
+		test.commit(m2).nrOfPassingLanes(0);
+		test.commit(m1).nrOfPassingLanes(0);
+		test.noMoreCommits();
+	}
+
 	/**
 	 * The graph shows the problematic original positioning. Due to this some
 	 * lanes are no straight lines here, but they are with the new layout code)

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

 downloadCancelled=Download cancelled
 downloadCancelledDuringIndexing=Download cancelled during indexing
 duplicateAdvertisementsOf=duplicate advertisements of {0}
-duplicateParents=The following parent was specified multiple times: {0}
 duplicateRef=Duplicate ref: {0}
 duplicateRemoteRefUpdateIsIllegal=Duplicate remote ref update is illegal. Affected remote name: {0}
 duplicateStagesNotAllowed=Duplicate stages not allowed

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

 	/***/ public String downloadCancelled;
 	/***/ public String downloadCancelledDuringIndexing;
 	/***/ public String duplicateAdvertisementsOf;
-	/***/ public String duplicateParents;
 	/***/ public String duplicateRef;
 	/***/ public String duplicateRemoteRefUpdateIsIllegal;
 	/***/ public String duplicateStagesNotAllowed;

org.eclipse.jgit/src/org/eclipse/jgit/lib/CommitBuilder.java

 import java.io.OutputStreamWriter;
 import java.io.UnsupportedEncodingException;
 import java.nio.charset.Charset;
-import java.text.MessageFormat;
 import java.util.List;
 
-import org.eclipse.jgit.internal.JGitText;
-
 /**
  * Mutable builder to construct a commit recording the state of a project.
  *
 	 *            branch being merged into the current branch.
 	 */
 	public void setParentIds(AnyObjectId parent1, AnyObjectId parent2) {
-		if (!parent1.equals(parent2))
-			parentIds = new ObjectId[] { parent1.copy(), parent2.copy() };
-		else
-			throw new IllegalArgumentException(MessageFormat.format(
-					JGitText.get().duplicateParents, parent1.getName()));
+		parentIds = new ObjectId[] { parent1.copy(), parent2.copy() };
 	}
 
 	/**
 	 *            the entire list of parents for this commit.
 	 */
 	public void setParentIds(ObjectId... newParents) {
-		ObjectId[] tmpIds = new ObjectId[newParents.length];
-
-		int newParentCount = 0;
-		for (int i = 0; i < newParents.length; i++) {
-			for (int j = 0; j < newParentCount; j++)
-				if (tmpIds[j].equals(newParents[i]))
-					throw new IllegalArgumentException(MessageFormat.format(
-							JGitText.get().duplicateParents,
-							tmpIds[j].getName()));
-			tmpIds[newParentCount++] = newParents[i].copy();
-		}
-		parentIds = tmpIds;
+		parentIds = new ObjectId[newParents.length];
+		for (int i = 0; i < newParents.length; i++)
+			parentIds[i] = newParents[i].copy();
 	}
 
 	/**
 	 *            the entire list of parents for this commit.
 	 */
 	public void setParentIds(List<? extends AnyObjectId> newParents) {
-		ObjectId[] tmpIds = new ObjectId[newParents.size()];
-
-		int newParentCount = 0;
-		for (AnyObjectId newId : newParents) {
-			for (int j = 0; j < newParentCount; j++)
-				if (tmpIds[j].equals(newId))
-					throw new IllegalArgumentException(MessageFormat.format(
-							JGitText.get().duplicateParents,
-							tmpIds[j].getName()));
-			tmpIds[newParentCount++] = newId.copy();
-		}
-		parentIds = tmpIds;
+		parentIds = new ObjectId[newParents.size()];
+		for (int i = 0; i < newParents.size(); i++)
+			parentIds[i] = newParents.get(i).copy();
 	}
 
 	/**
 		if (parentIds.length == 0) {
 			setParentId(additionalParent);
 		} else {
-			for (int i = 0; i < parentIds.length; i++)
-				if (parentIds[i].equals(additionalParent))
-					throw new IllegalArgumentException(MessageFormat.format(
-							JGitText.get().duplicateParents,
-							parentIds[i].getName()));
 			ObjectId[] newParents = new ObjectId[parentIds.length + 1];
 			System.arraycopy(parentIds, 0, newParents, 0, parentIds.length);
 			newParents[parentIds.length] = additionalParent.copy();