attr.c: read attributes in a sparse directory

Before this patch, git check-attr was unable to read the attributes from
a .gitattributes file within a sparse directory. The original comment
was operating under the assumption that users are only interested in
files or directories inside the cones. Therefore, in the original code,
in the case of a cone-mode sparse-checkout, we didn't load the
.gitattributes file.

However, this behavior can lead to missing attributes for files inside
sparse directories, causing inconsistencies in file handling.

To resolve this, revise 'git check-attr' to allow attribute reading for
files in sparse directories from the corresponding .gitattributes files:

1.Utilize path_in_cone_mode_sparse_checkout() and index_name_pos_sparse
to check if a path falls within a sparse directory.

2.If path is inside a sparse directory, employ the value of
index_name_pos_sparse() to find the sparse directory containing path and
path relative to sparse directory. Proceed to read attributes from the
tree OID of the sparse directory using read_attr_from_blob().

3.If path is not inside a sparse directory，ensure that attributes are
fetched from the index blob with read_blob_data_from_index().

Change the test 'check-attr with pathspec outside sparse definition' to
'test_expect_success' to reflect that the attributes inside a sparse
directory can now be read. Ensure that the sparse index case works
correctly for git check-attr to illustrate the successful handling of
attributes within sparse directories.

Helped-by: Victoria Dye <vdye@github.com>
Signed-off-by: Shuqi Liang <cheskaqiqi@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index 2d7fa65d81..dc84b3e2e1 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -2271,7 +2271,7 @@ test_expect_success 'check-attr with pathspec inside sparse definition' '
 	test_all_match git check-attr -a --cached -- deep/a
 '
 
-test_expect_failure 'check-attr with pathspec outside sparse definition' '
+test_expect_success 'check-attr with pathspec outside sparse definition' '
 	init_repos &&
 
 	echo "a -crlf myAttr" >>.gitattributes &&
@@ -2288,6 +2288,14 @@ test_expect_failure 'check-attr with pathspec outside sparse definition' '
 	test_all_match git check-attr -a --cached -- folder1/a
 '
 
+# NEEDSWORK: The 'diff --check' test is left as 'test_expect_failure' due
+# to an underlying issue in oneway_diff() within diff-lib.c.
+# 'do_oneway_diff()' is not called as expected for paths that could match
+# inside of a sparse directory. Specifically, the 'ce_path_match()' function
+# fails to recognize files inside a sparse directory (e.g., when 'folder1/'
+# is a sparse directory, 'folder1/a' cannot be recognized). The goal is to
+# proceed with 'do_oneway_diff()' if the pathspec could match inside of a
+# sparse directory.
 test_expect_failure 'diff --check with pathspec outside sparse definition' '
 	init_repos &&