Support receiving dry-validation contracts directly

lib/hanami/action/validatable.rb

@@ -187,12 +187,22 @@ def params(klass = nil, &block)
         # @api public
         # @since 2.2.0
         def contract(klass = nil, &block)
+          # TODO:
+          # 1. assign the contract class to the action
+          # 2. in .new, initialize the contract from its class and assign to an ivar
+          #    (this should mean we can support contracts with their own deps)
+          # 3. in #call, inject the contract instance into the params, which can then call it
           if klass.nil?
-            klass = const_set(PARAMS_CLASS_NAME, Class.new(Params))
-            klass.contract(&block)
+            params_class = const_set(PARAMS_CLASS_NAME, Class.new(Params))
+            params_class.contract(&block)
+          elsif klass < Dry::Validation::Contract
+            params_class = const_set(PARAMS_CLASS_NAME, Class.new(Params))
+            params_class.instance_variable_set(:@_validator, klass.new)
+          else
+            params_class = klass
           end
 
-          @params_class = klass
+          @params_class = params_class
         end
       end
     end

spec/support/fixtures.rb

@@ -1930,23 +1930,21 @@ def handle(request, response)
   end
 end
 
-class ExternalContractParams < Hanami::Action::Params
-  contract do
-    params do
-      required(:birth_date).filled(:date)
-      required(:book).schema do
-        required(:title).filled(:str?)
-      end
+class ExternalContract < Dry::Validation::Contract
+  params do
+    required(:birth_date).filled(:date)
+    required(:book).schema do
+      required(:title).filled(:str?)
     end
+  end
 
-    rule(:birth_date) do
-      key.failure("you must be 18 years or older") if value < Date.today << (12 * 18)
-    end
+  rule(:birth_date) do
+    key.failure("you must be 18 years or older") if value < Date.today << (12 * 18)
   end
 end
 
 class ExternalContractAction < ContractAction
-  contract ExternalContractParams
+  contract ExternalContract
 end
 
 class WhitelistedUploadDslContractAction < Hanami::Action

spec/unit/hanami/action/contract_spec.rb

@@ -25,7 +25,7 @@
     end
   end
 
-  describe "provided by a standlone params class using a contract" do
+  describe "provided by a standlone contract class" do
     let(:action) { ExternalContractAction.new }
 
     context "when it has errors" do