Re: [PATCH] unpack-trees: fix sparse directory recursion check

> From: Victoria Dye <vdye@github.com>
> 
> Ensure 'is_sparse_directory_entry()' receives a valid 'name_entry *' if one
> exists in the list of tree(s) being unpacked in 'unpack_callback()'.
> 
> Currently, 'is_sparse_directory_entry()' is called with the first
> 'name_entry' in the 'names' list of entries on 'unpack_callback()'. However,
> this entry may be empty even when other elements of 'names' are not (such as
> when switching from an orphan branch back to a "normal" branch). As a
> result, 'is_sparse_directory_entry()' could incorrectly indicate that a
> sparse directory is *not* actually sparse because the name of the index
> entry does not match the (empty) 'name_entry' path.
> 
> Fix the issue by using the existing 'name_entry *p' value in
> 'unpack_callback()', which points to the first non-empty entry in 'names'.
> Because 'p' is 'const', also update 'is_sparse_directory_entry()'s
> 'name_entry *' argument to be 'const'.
> 
> Finally, add a regression test case.
> 
> Reported-by: Derrick Stolee <derrickstolee@github.com>
> Signed-off-by: Victoria Dye <vdye@github.com>

> ---
>     unpack-trees: fix sparse directory recursion check
>     
>     This issue was found when the updates from v2.37.3 introduced a test
>     failure in a downstream test suite.
>     
>     The issue stems from the fact that, before v2.37.3, 'unpack_callback()'
>     could previously "assume" that 'names[0]' was non-empty if a cache entry
>     was unpacked as a sparse index. When b15207b8cf (unpack-trees: unpack
>     new trees as sparse directories, 2022-08-08)) was introduced, it
>     invalidated that assumption by allowing sparse directories to be
>     unpacked based on the contents of other 'names' entries, rather than
>     unnecessarily recursing into them and unpacking files individually. As a
>     result, certain scenarios could cause a sparse directory to be unpacked
>     then also recursively unpacked via 'traverse_trees_recursive()',
>     creating duplicate index entries.
> 
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1344%2Fvdye%2Fbugfix%2Fsparse-index-orphan-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1344/vdye/bugfix/sparse-index-orphan-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/1344
> 
>  t/t1092-sparse-checkout-compatibility.sh | 9 +++++++++
>  unpack-trees.c                           | 4 ++--
>  2 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
> index 0302e36fd66..b9350c075c2 100755
> --- a/t/t1092-sparse-checkout-compatibility.sh
> +++ b/t/t1092-sparse-checkout-compatibility.sh
> @@ -380,6 +380,15 @@ test_expect_success 'checkout with modified sparse directory' '
>  	test_all_match git checkout base
>  '
>  
> +test_expect_success 'checkout orphan then non-orphan' '
> +	init_repos &&
> +
> +	test_all_match git checkout --orphan test-orphan &&
> +	test_all_match git status --porcelain=v2 &&
> +	test_all_match git checkout base &&
> +	test_all_match git status --porcelain=v2
> +'
> +
>  test_expect_success 'add outside sparse cone' '
>  	init_repos &&
>  
> diff --git a/unpack-trees.c b/unpack-trees.c
> index 90b92114be8..bae812156c4 100644
> --- a/unpack-trees.c
> +++ b/unpack-trees.c
> @@ -1423,7 +1423,7 @@ static void debug_unpack_callback(int n,
>   * from the tree walk at the given traverse_info.
>   */
>  static int is_sparse_directory_entry(struct cache_entry *ce,
> -				     struct name_entry *name,
> +				     const struct name_entry *name,
>  				     struct traverse_info *info)
>  {
>  	if (!ce || !name || !S_ISSPARSEDIR(ce->ce_mode))
> @@ -1562,7 +1562,7 @@ static int unpack_callback(int n, unsigned long mask, unsigned long dirmask, str
>  			}
>  		}
>  
> -		if (!is_sparse_directory_entry(src[0], names, info) &&
> +		if (!is_sparse_directory_entry(src[0], p, info) &&
>  		    !is_new_sparse_dir &&
>  		    traverse_trees_recursive(n, dirmask, mask & ~dirmask,
>  						    names, info) < 0) {
> 
> base-commit: d42b38dfb5edf1a7fddd9542d722f91038407819