key merge strategy

[pi0]

(this is a primary draft to explain the idea)

Related: #138, #87

Sometime default defu merging strategy is not ideal. We could allow a custom defu merger but it is not initiative.

I was thinking to try with an object syntax like this:

{
  mergeStrategy: {
    modules: (a, b) => a.concat(b)
  }
}

(it could be backported to defu)

[cpreston321]

So you are thinking if mergeStrategy is defined in the user config vs the c12 config? Then we could eventually put this back in defu to then use defuFn & defuArray to then automatically handle this.

[pi0]

c12 config (controlled by nuxt for example). Yes we need a defuFn wrapper to use consistently every place in c12, that extends defuArray-like behavior and allows overriding behavior per-key with simple object. So for example nuxt can do reverse merge on modules array.

[cpreston321]

I'll try to implement this and give it a shot for a POC 💯 Thanks for the feedback

[pi0]

Implemented as simpler merger function so that end-users have full control #160