Feature: Allows procs with arity 1 to validate and use custom messages (#2333)

* refactor: validate_param! method

- now allows a proc to validate and use custom messages
- adds @proc_message instance variable
- creates the skip_validation? method to pass rubocops cyclomatic error

* Adds changelog entry

* Adds PR # to the changelog

* Properly formats the changelog line

* Places the changelog line in the correct order

* Adds default changelog message for future use

* Edits the changelog with a better description

* refactor: allows procs with an arity of 1

* Adds a test for when arity is > 1

Author: TheDevJoao

CHANGELOG.md

@@ -7,6 +7,7 @@
 * [#2330](https://github.com/ruby-grape/grape/pull/2330): Use ActiveSupport inflector - [@ericproulx](https://github.com/ericproulx).
 * [#2331](https://github.com/ruby-grape/grape/pull/2331): Memory optimization when running validators - [@ericproulx](https://github.com/ericproulx).
 * [#2332](https://github.com/ruby-grape/grape/pull/2332): Use ActiveSupport configurable - [@ericproulx](https://github.com/ericproulx).
+* [#2333](https://github.com/ruby-grape/grape/pull/2333): Use custom messages in parameter validation with arity 1 - [@thedevjoao](https://github.com/TheDevJoao).
 * Your contribution here.
 
 #### Fixes

lib/grape/validations/validators/values_validator.rb

@@ -43,7 +43,7 @@ def validate_param!(attr_name, params)
           unless check_values(param_array, attr_name)
 
           raise validation_exception(attr_name, message(:values)) \
-          if @proc && !param_array.all? { |param| @proc.call(param) }
+            if @proc && !validate_proc(@proc, param_array)
         end
 
         private
@@ -68,6 +68,17 @@ def check_excepts(param_array)
           param_array.none? { |param| excepts.include?(param) }
         end
 
+        def validate_proc(proc, param_array)
+          case proc.arity
+          when 0
+            param_array.all? { |_param| proc.call }
+          when 1
+            param_array.all? { |param| proc.call(param) }
+          else
+            raise ArgumentError, 'proc arity must be 0 or 1'
+          end
+        end
+
         def except_message
           options = instance_variable_get(:@option)
           options_key?(:except_message) ? options[:except_message] : message(:except_values)

spec/grape/validations/validators/values_spec.rb

@@ -30,6 +30,10 @@ def add_except(except)
         def include?(value)
           values.include?(value)
         end
+
+        def even?(value)
+          value.to_i.even?
+        end
       end
     end
   end
@@ -241,6 +245,18 @@ def include?(value)
       end
       get '/proc/message'
 
+      params do
+        requires :number, values: { value: ->(v) { ValuesModel.even? v }, message: 'must be even' }
+      end
+      get '/proc/custom_message' do
+        { message: 'success' }
+      end
+
+      params do
+        requires :input_one, :input_two, values: { value: ->(v1, v2) { v1 + v2 > 10 } }
+      end
+      get '/proc/arity2'
+
       params do
         optional :name, type: String, values: %w[a b], allow_blank: true
       end
@@ -692,5 +708,26 @@ def app
       expect(last_response.status).to eq 400
       expect(last_response.body).to eq({ error: 'type failed check' }.to_json)
     end
+
+    context 'when proc has an arity of 1' do
+      it 'accepts a valid value' do
+        get '/proc/custom_message', number: 4
+        expect(last_response.status).to eq 200
+        expect(last_response.body).to eq({ message: 'success' }.to_json)
+      end
+
+      it 'rejects an invalid value' do
+        get '/proc/custom_message', number: 5
+        expect(last_response.status).to eq 400
+        expect(last_response.body).to eq({ error: 'number must be even' }.to_json)
+      end
+    end
+
+    context 'when arity is > 1' do
+      it 'returns an error status code' do
+        get '/proc/arity2', input_one: 2, input_two: 3
+        expect(last_response.status).to eq 400
+      end
+    end
   end
 end