[PATCH 1/4] ref-cache.c: fix prefix matching in ref iteration

From: Victoria Dye <vdye@github.com>

Update 'cache_ref_iterator_advance' to skip over refs that are not matched by the given prefix.

Currently, a ref entry is considered "matched" if the entry name is fully contained within the prefix:

* prefix: "refs/heads/v1"
* entry: "refs/heads/v1.0"

OR if the prefix is fully contained in the entry name:

* prefix: "refs/heads/v1.0"
* entry: "refs/heads/v1"

The first case is always correct, but the second is only correct if the ref cache entry is a directory, for example:

* prefix: "refs/heads/example"
* entry: "refs/heads/"

Modify the logic in 'cache_ref_iterator_advance' to reflect these expectations:

1. If 'overlaps_prefix' returns 'PREFIX_EXCLUDES_DIR', then the prefix and
   ref cache entry do not overlap at all. Skip this entry.
2. If 'overlaps_prefix' returns 'PREFIX_WITHIN_DIR', then the prefix matches
   inside this entry if it is a directory. Skip if the entry is not a
   directory, otherwise iterate over it.
3. Otherwise, 'overlaps_prefix' returned 'PREFIX_CONTAINS_DIR', indicating
   that the cache entry (directory or not) is fully contained by or equal to
   the prefix. Iterate over this entry.

Note that condition 2 relies on the names of directory entries having the appropriate trailing slash. The existing function documentation of 'create_dir_entry' explicitly calls out the trailing slash requirement, so this is a safe assumption to make.

Signed-off-by: Victoria Dye <vdye@github.com>
---
 refs/ref-cache.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)