sparse-checkout and symlinks?

Dear git list,

sparse-checkout interacts badly with symlinks within a git repository: if b/file is a symlink to a/file, and the user asks for a sparse-checkout with only b/, they get a dead link (b/file points to nothing).

I initially assumed that replacing a file by a symlink to another file with the same content would not be observable by other users of the repository. This assumption is incorrect in presence of sparse checkouts.

I would find it natural to have sparse-checkout "follow symlinks". When checking b/file as the user requests, git would notice that it is a symlink and do one of the following:

1. if the link target a/file is not in the specified sparse checkout 
set, copy its content instead of creating a dead symlink
    (Downside: this could lead to duplication if several in-checkout 
files point to a/file.)
2. or add a/file to the sparse checkout set
    (Note: simply checking it out silently is not enough as 'reapply' 
would then drop it)

Does this sound reasonable to you? Would you have recommendations on 
what the interface for such a feature should look like?
- which of the alternatives above would you recommend?
- should this be enabled only by a new configuration or command-line 
option (to which subcommand?), how would you name it?

Thanks in advance

## More details on the use-case

I'm trying to reduce the working directory size of a gigabyte-large git repository ( https://github.com/typst/packages <https://github.com/typst/packages> ) which contains a substantial amount of duplicated files, by replacing duplicates by symlinks. The repository uses a continuous integration script to run automated tests on each proposed change, which uses sparse-checkout on only the directories listed as containing modified files.(The directories correspond to independent "packages" so it makes sense to check them separately.) This breaks when the modified directories contain symlinks to other, non-modified directories.