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

[Victoria Dye <vdye@github.com>]

Derrick Stolee wrote:
> 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

I'll reroll with corrected CC's & make the `strlen` -> `*path` change.
Thanks!