Cannot commit this package when installed via composer

[mlambley]

Good day,

My composer file looks like the following:

{
    "minimum-stability": "dev",
    "prefer-stable": true,
    "require": {
        "psr/http-message": "1.0",
        "slim/slim": "^3.8.1",
        "respect/validation": "^1.1",
        "rszrama/negotiation-middleware": "dev-master"
    }
}

When I do composer update and install, the files install on my machine. That is not the problem. But with every other package in my vendor directory, I can commit the full source code to my own project, without the need for submodule unpacking. Instead, git is reporting that these files are "under version control" and won't commit them.

Am I supposed to be retrieving this package via a submodule? I see no options for installing via a submodule in this package's readme - only via composer.

I would prefer to install this package via composer and commit the full code to my project like I do with every other. Please assist with this. Thank you.