Kenji Integration: declare input validations declaratively vs. run them as code

[kballenegger]

Crazy idea:

In Kenji, an input validation might be written declaratively, above the route, instead of as code within the route.

Code could look like this:

validate! do
  # symbols are path params
  validates_type_of :id, is: Blah
  # string are body keys
  validates_type_of 'name', is: String
end
post '/friends/:id' do 
  # method body
end

Or:

post '/friends/:id',
  validate: -> {
    # symbols are path params
    validates_type_of :id, is: Blah
    # string are body keys
    validates_type_of 'name', is: String
  } do
  # method body
end

Here, we gain the ability to:

1. validate path params, and passed vars, instead of only body
2. run validations only with no additional code (magic VALIDATE http method)