Composer require local package

The way to link to a local, in-development package is to first add in your main project's composer.json a repository, like this:

"repositories": [
    {
        "type": "path",
        "url": "/full/or/relative/path/to/development/package"
    }
]

You also need to either have a version specified in your development package's composer.json or the way I do it is to require the package using @dev, like this:

composer require "vendorname/packagename @dev"

It should output:

- Installing vendor/packagename (dev-develop)
Symlinked from /full/or/relative/path/to/development/package

The @dev in the require command is important, composer uses this to pickup the source code and symlink it to your new package.

It's a stability flag added to the version constraint (see package link).

These allow you to further restrict or expand the stability of a package beyond the scope of the minimum-stability setting.

The minimum-stability flags are:

Available options (in order of stability) are dev, alpha, beta, RC, and stable.

You can use Composer's repositories feature

https://getcomposer.org/doc/05-repositories.md#path

{
  "repositories": [
    {
        "type": "path",
        "url": "../../packages/my-package"
    }
  ],
  "require": {
    "my/package": "*"
  }
}

Instead of using the http format, specify a file path on disk.