Improve --plugins resolution algorithm

[alekseykulikov]

First of all, thank you for adding the way to define plugins. It's a fantastic feature!

We've just published the lighthouse-plugin-field-performance and discovered a few issues with --plugins resolution algorithm.

The story:

1. Start local development using the recipe. It's not possible to run the current folder as a plugin since Lighthouse expects lighthouse-plugin- prefix. I have added the folder lighthouse-plugin-field-performance with all the related code.
2. Release 🎉Check the published module, but --plugins algorithm does not recognize package.json's main field and can't find the code. So we used the exact structure from the recipe and ln -s ../ node_modules/lighthouse-plugin-field-performance a symlink to use the current directory as a part of node_modules.
3. plugin.js is a wrong name since it can only resolve index.js.

The whole story explained with commit messages:

Conclusion
In order to make the development of the plugins more straightforward, it would be great to improve --plugins resolution algorithm by adding support for package.json's main field and checking if the current folder is a lighthouse plugin. (for example, checking the name in package.json).

[patrickhulce]

Thanks for filing and being such an early adopter! :D

The behavior you'd like is the current intended behavior and the lighthouse-plugin-example works locally for me using "main": "./plugin.js" so we definitely want to make sure this is the experience for plugin developers as well.

A few notes:

It's not possible to run the current folder as a plugin since Lighthouse expects lighthouse-plugin- prefix.

Right now I get this to work by doing yarn add ./path/to/lighthouse-plugin-folder at which point its put into node_modules with the proper structure.

--plugins algorithm does not recognize package.json's main field and can't find the code

Our algorithm is require.resolve so if it can be required exactly as you pass it in to --plugins then it should work with us. If that doesn't work we start falling back to some workarounds but if it's in node_modules and require.resolve works, it should work here too.

If I edit your plugin locally back to plugin.js and a main property, it works as expected when I invoke it with lighthouse https://example.com --plugins=lighthouse-plugin-field-performance. Maybe I'm missing some additional information to bump into this though?

[alekseykulikov]

Thank you for a kind detailed reply! You are absolutely right!

I've just found the typo in our package.json which uses source instead of main 🤦‍♂️
https://github.com/treosh/lighthouse-plugin-field-performance/blob/master/package.json#L8

Great tip with yarn add ./path/to/local. I will update the repo.