Re: [PATCH v2 0/3] Fix behavior of worktree config in submodules

> About a year ago, discussion on the sparse index integration of 'git grep'
> surfaced larger incompatibilities between sparse-checkout and submodules
> [1]. This series fixes one of the underlying issues to that incompatibility,
> which is that the worktree config of the submodule (where
> 'core.sparseCheckout', 'core.sparseCheckoutCone', and 'index.sparse' are
> set) is not used when operating on the submodule from its super project
> (e.g., in a command with '--recurse-submodules').
> 
> The outcome of this series is that 'extensions.worktreeConfig' and the
> contents of the repository's worktree config are read and applied to (and
> only to) the relevant repo when working in a super project/submodule setup.
> This alone doesn't fix sparse-checkout/submodule interoperability; the
> additional changes needed for that will be submitted in a later series. I'm
> also hoping this will help (or at least not hurt) the work to avoid use of
> global state in config parsing [2].
> 
> 
> Changes since V1
> ================
> 
>  * In 't3007', replaced manual 'git config'/'test_when_finished "git config
>    --unset"' pairs with 'test_config' helper. Updated 'test_config' to
>    handle the '--worktree' option.
>  * Updated commit messages & test comments to better explain the purpose and
>    more subtle functionality details to the new tests
>  * Added a commit to move 'struct repository' out of 'git_config_source',
>    rather than creating a dummy 'config_source' just to hold a repository
>    instance.
>  * Changed the config setting in the new tests from 'feature.experimental'
>    to 'index.sparse' to tie these changes to their intended use case.
>  * "super project" -> "superproject"