Following on from my comments at https://github.com/wikimedia/composer-merge-plugin/pull/189#issuecomment-771280032...
`ComposerJson::getRequiredDependencies` only gets the `"require"` items from the root composer.json... We don't do anything to make sure the requires of files included in `composer.local.json` via the composer merge-plugin are actually installed/resolved...
composer-merge-plugin is in requires itself... Can we make MW call code to check things are all resolved nicely?
It would seem useful for the edge cases of the plugin and composer upgrades in one go... And also when someone adds something to composer.local.json, but then never run `composer update`... It's certainly possible their wiki may break from not having had an extensions composer requirements resolved and installed...