Composer require inline alias

Here’s a feature of composer that I didn’t know about until a few days ago – require inline alias.  Here’s the example from the documentation:

{
    "repositories": [
        {
            "type": "vcs",
            "url": "https://github.com/you/monolog"
        }
    ],
    "require": {
        "symfony/monolog-bundle": "2.0",
        "monolog/monolog": "dev-bugfix as 1.0.x-dev"
    }
}

This is super useful when you have dependencies in your project that require a particular version of a third-party library or plugin, and you want to try a branch of that library or plugin. Switching to the branch alias doesn’t solve the problem, as everything that has version constraints on that requirement, will complain. With inline alias, you can alias a particular branch of the dependency as a particular version.

With inline alias, composer will fetch the branch that you want, but will assume that that branch works as a particular version that you specify, and thus satisfy all the other dependencies that require that particular version.

In my particular case, I was working on the CakePHP-based application, which was using a few CakePHP plugins (installed via composer).  Those plugins require CakePHP v3+.  I wanted to test a branch of CakePHP which had a particular fix I was interested in, but without disabling all the plugins.  Switching my application’s composer to require a branch dissatisfied all the plugins, as now composer didn’t know if the branch that I am requiring is of the CakePHP v3 or not.  Aliasing the branch to v3.4.1 (current stable version at the time) worked like a charm.