Offer a way to pass configuration structures to plugins

[atrauzzi]

One particular plugin I have in mind is to integrate with my application framework ( https://github.com/atrauzzi/protoculture ).

To do this, I need to instantiate a subclass of my "root" application class which would live inside the gatsby project itself. If I made a gatsby plugin as an npm package, I'd need some way to inform the plugin where it can find that root subclass from the current gatsby project. Something like:

• Root subclass is found at: src/Protoculture.ts
• [the configuration feature desired] imports and holds a reference to the root subclass constructor
• My gatsby-browser.tsx somehow receives and inspects this config
• My gatsby-browser.tsx instantiates the root application in onClientEntry, which kicks off into my DI ecosystem allowing me to resolve out things like redux and other goodies

( Cheap plug: @KyleAMathews - feel free to look at protoculture for inspiration as it's all about application structure. It might offer you some ideas for things like #858 . FWIW, protoculture is inspired by the laravel web framework and countless other DI systems. )

[KyleAMathews]

Perhaps I'm missing something? Plugins can take options.

[atrauzzi]

Haha, oh! Where do you set the options? I think I'm the one not seeing it at this point, lol.

#hiimnew