Fix crashes on rare combination of file names

The NameConflictTreeWalk class is used in merge for iterating over
entries in commits. The class uses a separate iterator for each
commit's tree. In rare cases it can incorrectly report the same entry
twice. As a result, duplicated entries are added to the merge result
and later jgit throws an exception when it tries to process merge
result.

The problem appears only when there is a directory-file conflict for
the last item in trees. Example from the bug:
Commit 1:
* subtree - file
* subtree-0 - file
Commit 2:
* subtree - directory
* subtree-0 - file
Here the names are ordered like this:
"subtree" file <"subtree-0" file < "subtree" directory.

The NameConflictTreeWalk handles similar cases correctly if there are
other files after subtree... in commits - this is processed in the
AbstractTreeIterator.min function. Existing code has a special
optimization for the case, when all trees are pointed to the same
entry name - it skips additional checks. However, this optimization
incorrectly skips checks if one of trees reached the end.

The fix processes a situation when some trees reached the end, while
others are still point to an entry.

bug: 535919
Change-Id: I62fde3dd89779fac282479c093400448b4ac5c86

0 files changed, 0 insertions, 0 deletions