We reused the cache-tree data without verifying the tree object
still exists. Recompute in cache_tree_update() an otherwise
valid cache-tree entry when the tree object disappeared.
This is not usually a problem, but theoretically without this
fix things can break when the user does something like this:
- read-index from a side branch
- write-tree the result
- remove the side branch with "git branch -D"
- remove the unreachable objects with "git prune"
- write-tree what is in the index.
Signed-off-by: Junio C Hamano <junkio@cox.net>
The cache_tree data structure is to cache tree object names that
would result from the current index file.
The idea is to have an optional file to record each tree object
name that corresponds to a directory path in the cache when we
run write_cache(), and read it back when we run read_cache().
During various index manupulations, we selectively invalidate
the parts so that the next write-tree can bypass regenerating
tree objects for unchanged parts of the directory hierarchy.
We could perhaps make the cache-tree data an optional part of
the index file, but that would involve the index format updates,
so unless we need it for performance reasons, the current plan
is to use a separate file, $GIT_DIR/index.aux to store this
information and link it with the index file with the checksum
that is already used for index file integrity check.
Signed-off-by: Junio C Hamano <junkio@cox.net>
