Merge branch 'vd/sparse-reset' into ld/sparse-diff-blame

* vd/sparse-reset:
  unpack-trees: improve performance of next_cache_entry
  reset: make --mixed sparse-aware
  reset: make sparse-aware (except --mixed)
  reset: integrate with sparse index
  reset: expand test coverage for sparse checkouts
  sparse-index: update command for expand/collapse test
  reset: preserve skip-worktree bit in mixed reset
  reset: rename is_missing to !is_in_reset_tree

cache.h

@@ -816,6 +816,16 @@ 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