From be995c1c35b55c5449bf0ce683724e7ce6ada036 Mon Sep 17 00:00:00 2001
From: Marc Rohloff <marc@marcrohloff.com>
Date: Fri, 8 May 2026 09:40:15 -0600
Subject: [PATCH 1/2] Feature: Handle symbol-to-proc wrappers (`&:`) that refer
 to a method created using delegation or method missing

These methods have an arity of -1
---
 CHANGELOG.md                     |  2 ++
 lib/grape_entity/entity.rb       |  3 +-
 spec/grape_entity/entity_spec.rb | 47 ++++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 98b796c..9ebd9ea 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,7 @@
 ### Next Release
 
+* [#406](https://github.com/ruby-grape/grape-entity/pull/406): Handle symbol-to-proc wrappers (`&:method_name`) where the method uses `delegate` or `method_missing`
+
 #### Features
 
 * Your contribution here.
diff --git a/lib/grape_entity/entity.rb b/lib/grape_entity/entity.rb
index cd14033..1ca44ef 100644
--- a/lib/grape_entity/entity.rb
+++ b/lib/grape_entity/entity.rb
@@ -548,7 +548,8 @@ def ensure_block_arity!(block)
       end
 
       arity = object.method(origin_method_name).arity
-      return if arity.zero?
+      # functions defined using `delegate` or `method_missing` have an arity of -1
+      return if arity <= 0
 
       raise ArgumentError, <<~MSG
         Cannot use `&:#{origin_method_name}` because that method expects #{arity} argument#{'s' if arity != 1}.
diff --git a/spec/grape_entity/entity_spec.rb b/spec/grape_entity/entity_spec.rb
index 5bdd73e..7e727fc 100644
--- a/spec/grape_entity/entity_spec.rb
+++ b/spec/grape_entity/entity_spec.rb
@@ -400,6 +400,14 @@ class BogusEntity < Grape::Entity
 
         describe 'blocks' do
           class SomeObject
+            class SomeObjectDelegate
+              def method_using_delegation
+                'delegated-result'
+              end
+            end
+
+            delegate :method_using_delegation, to: :delegate_object
+
             def method_without_args
               'result'
             end
@@ -415,6 +423,23 @@ def method_with_multiple_args(_object, _options)
             def raises_argument_error
               raise ArgumentError, 'something different'
             end
+
+            def method_missing(method, ...)
+              return 'missing-result' if method.to_sym == :method_using_missing
+
+              super
+            end
+
+            def delegate_object
+              @delegate_object ||= SomeObjectDelegate.new
+            end
+
+            private
+
+            def respond_to_missing?(method, include_private = false)
+              method.to_sym == :method_using_missing ||
+                super
+            end
           end
 
           describe 'with block passed in' do
@@ -459,6 +484,28 @@ def raises_argument_error
             end
           end
 
+          context 'with block passed in via & that uses `missing_method`' do
+            specify do
+              subject.expose :using_missing, &:method_using_missing
+
+              object = SomeObject.new
+              expect(object.method(:method_using_missing).arity).to eq(-1)
+              value = subject.represent(object).value_for(:using_missing)
+              expect(value).to eq('missing-result')
+            end
+          end
+
+          context 'with block passed in via & that uses `delegate`' do
+            specify do
+              subject.expose :using_delegation, &:method_using_delegation
+
+              object = SomeObject.new
+              expect(object.method(:method_using_delegation).arity).to eq(-1)
+              value = subject.represent(object).value_for(:using_delegation)
+              expect(value).to eq('delegated-result')
+            end
+          end
+
           context 'with block passed in via &' do
             specify do
               subject.expose :that_method_with_one_arg, &:method_with_one_arg

From 9a21bb24e474279a555347f3691dc913c43beb10 Mon Sep 17 00:00:00 2001
From: Marc Rohloff <marc@marcrohloff.com>
Date: Sat, 9 May 2026 15:28:46 -0600
Subject: [PATCH 2/2] Fix CI issues

---
 CHANGELOG.md                     | 2 +-
 CONTRIBUTING.md                  | 2 +-
 spec/grape_entity/entity_spec.rb | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9ebd9ea..6568d3d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,6 @@
 ### Next Release
 
-* [#406](https://github.com/ruby-grape/grape-entity/pull/406): Handle symbol-to-proc wrappers (`&:method_name`) where the method uses `delegate` or `method_missing`
+* [#406](https://github.com/ruby-grape/grape-entity/pull/406): Handle symbol-to-proc wrappers (`&:method_name`) where the method uses `delegate` or `method_missing` - [@marcrohloff](https://github.com/marcrohloff).
 
 #### Features
 
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 6023a84..655e94e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -44,7 +44,7 @@ Implement your feature or bug fix.
 
 Ruby style is enforced with [Rubocop](https://github.com/bbatsov/rubocop), run `bundle exec rubocop` and fix any style issues highlighted.
 
-Make sure that `bundle exec rake` completes without errors.
+Make sure that `bundle exec rake` and `rubocop` completes without errors.
 
 #### Write Documentation
 
diff --git a/spec/grape_entity/entity_spec.rb b/spec/grape_entity/entity_spec.rb
index 7e727fc..527aa5b 100644
--- a/spec/grape_entity/entity_spec.rb
+++ b/spec/grape_entity/entity_spec.rb
@@ -436,7 +436,7 @@ def delegate_object
 
             private
 
-            def respond_to_missing?(method, include_private = false)
+            def respond_to_missing?(method, include_private = false) # rubocop:disable Style/OptionalBooleanParameter
               method.to_sym == :method_using_missing ||
                 super
             end