Re: [PATCH 1/7] sparse-index: prevent repo root from becoming sparse

[Derrick Stolee <derrickstolee@github.com>]

On 2/23/2022 1:25 PM, Victoria Dye via GitGitGadget wrote:
> From: Victoria Dye <vdye@github.com>

Aside: It looks like you have the same "mailto:" email addresses in the
CC similar to a mistake I made. The root cause of my issue was that I
copy-pasted from the rendered description of another PR instead of
copying the plaintext available by clicking the "Edit" button. Perhaps
this is worth extending GGG to prevent this issue in the future.

> Prevent the repository root from being collapsed into a sparse directory by
> treating an empty path as "inside the sparse-checkout". When collapsing a
> sparse index (e.g. in 'git sparse-checkout reapply'), the root directory
> typically could not become a sparse directory due to the presence of in-cone
> root-level files and directories. However, if no such in-cone files or
> directories were present, there was no explicit check signaling that the
> "repository root path" (an empty string, in the case of
> 'convert_to_sparse(...)') was in-cone, and a sparse directory index entry
> would be created from the repository root directory.
> 
> The documentation in Documentation/git-sparse-checkout.txt explicitly states
> that the files in the root directory are expected to be in-cone for a
> cone-mode sparse-checkout. Collapsing the root into a sparse directory entry
> violates that assumption, as sparse directory entries are expected to be
> outside the sparse cone and have SKIP_WORKTREE enabled. This invalid state
> in turn causes issues with commands that interact with the index, e.g.
> 'git status'.
> 
> Treating an empty (root) path as in-cone prevents the creation of a root
> sparse directory in 'convert_to_sparse(...)'. Because the repository root is
> otherwise never compared with sparse patterns (in both cone-mode and
> non-cone sparse-checkouts), the new check does not cause additional changes
> to how sparse patterns are applied.

Good catch! I agree with everything said here.

> +	if (!strlen(path) ||

Instead of a full strlen(), could we just check "if (!*path ||" to
look for the nul byte?

Thanks,
-Stolee