How to write an odd case version constraint for composer?

Question

The constraint that I am interested in is

"require":{ "php": "..."

Is there a way to target php 7.1 for the project packages in composer.json even though I'm running 7.2 when I call composer update/install on the command line?

Answer 1

You can use platform configuration from Composer: https://getcomposer.org/doc/06-config.md#platform

Basically, your composer.json would look like this:

{
    "require": {
        ...
    },
    "config": {
        "platform": {
            "php": "7.1"
        }
    }
}

This will make sure that you install only packages compatible with PHP 7.1, no matter which PHP version you use to actually install the packages.