validation: fix active_model should not fail on undeclared attributes

README.md

@@ -65,7 +65,9 @@ evaluated in the context of a class. I advise to keep things simple; `attribute`
 and `validates` should be all you need in order to do basic validation.
 
 `contract` will dynamically create a class, will create the object initializing
-it with the context's key/value pairs as attributes, then it will be validated.
+it with the context's key/value pairs also declared as attributes in the contract
+(in composition a single interactor can't be responsible to validate the whole
+context, but just the data it needs), then it will be validated.
 
 If the context is invalid it's errors messages will be copied into context's
 `errors`, thus making it a failed one.

lib/i_do_not_need_interactor/contract/active_model.rb

@@ -7,7 +7,7 @@ module Contract
     module ActiveModel # rubocop:disable Style/Documentation
       def self.included(descendant) # rubocop:disable Metrics/MethodLength
         class << descendant
-          def contract(&block)
+          def contract(&block) # rubocop:disable Metrics/MethodLength
             caller = self
             @contract = Class.new do
               set_temporary_name("#{caller.inspect.downcase}::contract")
@@ -18,15 +18,25 @@ def contract(&block)
               def self.model_name
                 ::ActiveModel::Name.new(self, nil, "temp")
               end
+
+              def self.build_for_interactor_validation(ctx)
+                contract = new
+                declared_attributes = contract.attribute_names.each(&:to_sym)
+                context_attributes_to_validate = ctx.slice(declared_attributes)
+                contract.assign_attributes(context_attributes_to_validate)
+                contract
+              end
             end
             @contract.class_exec(&block)
           end
         end
       end
 
       def validate(ctx)
-        self.class.instance_variable_get(:@contract).new(**ctx).validate!
-      rescue ::ActiveModel::ValidationError, ::ActiveModel::UnknownAttributeError => e
+        self.class.instance_variable_get(:@contract)
+            .build_for_interactor_validation(ctx)
+            .validate!
+      rescue ::ActiveModel::ValidationError => e
         ctx.errors << e.message
       end
     end

test/test_i_do_not_need_interactor.rb

@@ -134,10 +134,11 @@ def test_contract_active_model_integration
     assert_equal ["Validation failed: Test can't be blank"], outcome.errors
   end
 
-  def test_contract_active_model_integration_with_unknown_attribute
-    outcome = InteractorWithActiveModelContract.call(foo: 1)
+  def test_contract_active_model_integration_validates_only_declared_attributes
+    undeclared_attribute = { foo: 1 }
+    outcome = InteractorWithActiveModelContract.call(undeclared_attribute)
 
-    assert_equal ["unknown attribute 'foo' for interactorwithactivemodelcontract::contract."], outcome.errors
+    assert_equal ["Validation failed: Test can't be blank"], outcome.errors
   end
 
   def test_contract_dry_validation_integration
@@ -146,6 +147,13 @@ def test_contract_dry_validation_integration
     assert_equal [{ test: ["is missing"] }], outcome.errors
   end
 
+  def test_contract_dry_validation_integration_validates_only_declared_attributes
+    undeclared_attribute = { foo: 1 }
+    outcome = InteractorWithDryValidationContract.call(undeclared_attribute)
+
+    assert_equal [{ test: ["is missing"] }], outcome.errors
+  end
+
   def test_manual_validation
     outcome = InteractorWithManualValidation.call