What is a subproject commit?

Solution 1:

A submodule commit is a gitlink, special entry recorded in the index, created when you add a submodule to your repo;

It records the SHA1 currently referenced by the parent repo.

A git submodule update --init is enough to populate the laravel subdirectory in your repo.

Once it is filled, note that your submodule repo is in a detached HEAD mode.

As shown here, when switching branches in the parent repo, your submodule gitlink will change accordingly, but your submodule content won't change until you make again a git submodule update (after the git checkout)

Solution 2:

It means the repository uses Submodules.

To pull down the Laravel code, try

git submodule init
git submodule update

Submodules are notoriously prickly; I recommend reading up on them before working too much on a project that uses them. The link above should be a good starting point.