Accessing endpoint's params

Goal

I want to test params of the endpoint without making additional request because it makes tests quicker and more readable.

Context

It would be nice to be able to access param list of the endpoint just by initializing the class. If we have a class:

class MyApi < Grape::API
  params do
    requires :id, type: Integer, positive_value: true # positive_value - is a custom validation
  end
  
  get '/foo' do
    # ...
  end
end

Let's consider very simple interface to make it obvious. There can be a method MyApi.new.action_params(:get, '/foo') and it returns a list:

{ 
  id: {type: Integer, required: true, custom_validations: [:positive_value]
} 

And specs may look like:

describe 'checking GET /foo params' do
  subject { MyApi.new.action_params(:get, '/foo') }
  it { is_expected[:id].to eq((:type: 'Integer', required: true, custom_validations: []) }
end

Suggestion

Return array of classes EndpointParam:

class EndpointParam < Dry::Struct
  attribute :name, Types::String
  attribute :required, Types::Bool
  attribute :type, Types::Any
  attribute :custom_validators, Types::Array.of(EndpointParam)
end

Matcher:

describe 'checking GET /foo params' do
  subject { MyApi.new.action_params(:get, '/foo')  } 
  it { is_expected.to have_param(:id).with_type(Types::String).being_required.with_custom_validators(:positive_value) }
end

It was discussed here https://groups.google.com/forum/#!topic/ruby-grape/uww_W6c7Obs and examples are got also from there

No files, tests, or entry points are named. Start by reviewing how Grape::API currently stores endpoint parameter declarations and read the linked ruby-grape discussion; define the public inspection interface and its parameter representation before adding coverage. Done means endpoint parameters, requiredness, types, and custom validations can be inspected without an additional request.