reset: make sparse-aware (except --mixed)

Remove `ensure_full_index` guard on `prime_cache_tree` and update
`prime_cache_tree_rec` to correctly reconstruct sparse directory entries in
the cache tree. While processing a tree's entries, `prime_cache_tree_rec`
must determine whether a directory entry is sparse or not by searching for
it in the index (*without* expanding the index). If a matching sparse
directory index entry is found, no subtrees are added to the cache tree
entry and the entry count is set to 1 (representing the sparse directory
itself). Otherwise, the tree is assumed to not be sparse and its subtrees
are recursively added to the cache tree.

Helped-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/cache.h b/cache.h
index 3e5658c..5212ea2 100644
--- a/cache.h
+++ b/cache.h
@@ -817,6 +817,16 @@ struct cache_entry *index_file_exists(struct index_state *istate, const char *na
 int index_name_pos(struct index_state *, const char *name, int namelen);
 
 /*
+ * Determines whether an entry with the given name exists within the
+ * given index. The return value is 1 if an exact match is found, otherwise
+ * it is 0. Note that, unlike index_name_pos, this function does not expand
+ * the index if it is sparse. If an item exists within the full index but it
+ * is contained within a sparse directory (and not in the sparse index), 0 is
+ * returned.
+ */
+int index_entry_exists(struct index_state *, const char *name, int namelen);
+
+/*
  * Some functions return the negative complement of an insert position when a
  * precise match was not found but a position was found where the entry would
  * need to be inserted. This helper protects that logic from any integer