GSoC week5-6

week5-6

This week, I started to delve into the source code of git check-attr with the goal of creating an effective test. git_check_attr operates by iterating over all attributes listed in the attr_check structure. It checks the values of these attributes for a specific file and subsequently stores the results back into the attr_check structure. This mechanism enables simultaneous querying of multiple attributes, eliminating the need for repeated function calls. After examining the source code, I crafted my first test which, to my delight, passed in its entirety. This led me to believe that this command had been successfully integrated with the sparse command at some point. However, this assumption was later proven incorrect.

test_expect_success 'check-attr with pathspec inside sparse definition' '
    init_repos &&

    echo "a -crlf myAttr" >>.gitattributes &&
    run_on_all cp ../.gitattributes . &&

     git check-attr -a -- deep/a &&

    test_all_match git add deep/.gitattributes &&
    test_all_match git check-attr -a --cached -- deep/a
'

test_expect_success 'check-attr with pathspec inside sparse definition' '
    init_repos &&

     "a -crlf myAttr" >>.gitattributes &&
    run_on_all cp ../.gitattributes . &&

    test_all_match git check-attr -a -- folder1/a &&

    test_all_match git add folder1/.gitattributes &&
    test_all_match git check-attr -a --cached -- folder1/a
'

In the context of the read_attr function, when direction is set to GIT_ATTR_INDEX, the attributes are fetched from the index. If the direction is GIT_ATTR_CHECKOUT, an attempt is made to read the attributes from the index first, and if unsuccessful, the function tries to retrieve them from the file. Similarly, if the direction is GIT_ATTR_CHECKIN, the attributes are initially attempted to be read from the file, and if this fails, the function tries to fetch them from the index.

The process of extracting attributes from the index is carried out by the read_attr_from_index function. It utilizes the path_in_cone_mode_sparse_checkout function to verify if the specified path falls within the sparse checkout scope. If it doesn’t, the function returns NULL. This sheds light on why the aforementioned test was successful; instead of searching for attributes in the index, we were traversing the working tree for the ‘.gitattributes’ file in all instances of this test.

My mentor, Victoria, identified a limitation in this code. She explained that if someone need to read the attributes of a file located within a sparse directory, it’s necessary to read attributes from any ‘.gitattributes’ files that might be present in that sparse directory. She suggested that I should read the blob OIDs from the tree entry of the sparse directory, citing the example of “builtin/grep.c: integrate with sparse index”.