I really like where this is going, in fact I love it, but before we merge this maybe we can do even better?

Lets say I want to enable for an entire API. How would I do that?

I feel like this is a DSL opportunity. For example declared params do ... or required params do or only params do or even strong params do? What do you think?

Doing this at a top level for an entire API (across multiple endpoints) is an interesting idea for those who really want to lock things down. But I think you meant applying it at the level of a single param block and all subordinate blocks. If we were going to do that, I'd probably opt for something like params allow_undeclared: false do. (Similar to allow_blank for individual params.)

That said, I've just realized that there's a bug with route_param that I need to fix -- so don't merge this yet!

I like allow_undeclared: true/false a lot more, thanks @jlfaber. Don't love the name but don't feel strongly about it. Maybe allow_any? Again no strong feelings.

I did mean for the entire API. If I were building a brand new service I'd want this to be the default behavior of all my params. I would do this through an extension:

class MyAPI < Grape::API
   include Grape::Params::AllowAny::False

end

@jlfaber Can I help with this? Lets finish it for 1.0?

This is awesome, and would help our QA team a lot with mistakes in cURL payloads when testing endpoints.

Is there anything I can do to help move this towards completion?

If anyone would like to pick this up, I'm absolutely good with it. I put the brakes on earlier because (IIRC) there were still issues dealing with inherited params (route params and explicit ones), especially when using mounted APIs. It's a bit fuzzy.

We ended up going in a different direction (JSON Schema) to accomplish what we needed so I can't prioritize working this issue right now. So if someone would like to pick up the torch, you absolutely have my blessing! Sorry to have left this hanging so long!

No worries @jlfaber - thanks for the info!

I'll see about carrying on the work you started.

I've rebased your branch with master and raised a new PR at #1729 - this PR can be closed.

Awesome! Thanks!