💡 Enable metro plugin when expo is installed

[DaniFoldi]

Suggest an idea for Knip

Hi 👋,

Expo is a complicated framework, because (unlike others, eg. next or astro which rely on build tools and wrap their configuration) it uses babel/metro config files. Expo depends on @expo/metro, which depends on all the metro tools, but that's not important here.

A project does not need metro in its package.json directly installed, and thus the metro plugin is not activated, and the metro config file is reported as unused. Reference: https://docs.expo.dev/guides/customizing-metro/
Babel is in a similar situation, although in all of the RN/expo projects I've seen where babel.config.js was explicitly added (neither is required, but for customization it's supported), @babel/transform and others were directly depended upon, so it's not as useful to infer in my opinion.

I was looking at the existing expo and metro plugins, and my current best idea is to add expo to the enablers of the metro plugin - but it's possible that there is a better way, hence this issue instead of a PR. Let me know if this is the right approach, or I'd missed a way to cross-reference plugins, happy to add it.

[webpro]

That could work.

Just last week we've managed to split up React Native from Metro plugin so at least things are organized slightly better today. The matter sounds pretty similar to e.g. #1528 and #1538.

Probably a good way to go about this is to create a new minimal fixture directory that represents the real-world scenario that should be supported (see other related fixtures/tests to get the idea). Or maybe adjust an existing one if that makes sense. Make the change and make the new test pass... 🚦

Typically plugins have their own "enablers", and sometimes e.g. entry or config or resolveConfig from another plugin is referenced/used (e.g. vite just uses vitest resolveConfig).