Fixes methods defined on included modules after remountable APIs (#1818)

Author: myxoh

CHANGELOG.md

@@ -4,7 +4,7 @@
 
 * Your contribution here.
 * [#1813](https://github.com/ruby-grape/grape/pull/1813): Add ruby 2.5 support, drop 2.2. Update rails version in travis - [@darren987469](https://github.com/darren987469).
-* [#1803](https://github.com/ruby-grape/grape/pull/1803): Adds the ability to re-mount all endpoints in any location - [@myxoh](https://github.com/bschmeck).
+* [#1803](https://github.com/ruby-grape/grape/pull/1803): Adds the ability to re-mount all endpoints in any location - [@myxoh](https://github.com/myxoh).
 * [#1795](https://github.com/ruby-grape/grape/pull/1795): Fix vendor/subtype parsing of an invalid Accept header - [@bschmeck](https://github.com/bschmeck).
 * [#1791](https://github.com/ruby-grape/grape/pull/1791): Support `summary`, `hidden`, `deprecated`, `is_array`, `nickname`, `produces`, `consumes`, `tags` options in `desc` block - [@darren987469](https://github.com/darren987469).
 

lib/grape/api.rb

@@ -7,7 +7,8 @@ module Grape
   class API
     # Class methods that we want to call on the API rather than on the API object
     NON_OVERRIDABLE = %I[define_singleton_method instance_variable_set inspect class is_a? ! kind_of?
-                         respond_to? const_defined? const_missing parent parent_name name equal? to_s parents].freeze
+                         respond_to? respond_to_missing? const_defined? const_missing parent
+                         parent_name name equal? to_s parents].freeze
 
     class << self
       attr_accessor :base_instance, :instances
@@ -81,6 +82,19 @@ def respond_to?(method, include_private = false)
         super(method, include_private) || base_instance.respond_to?(method, include_private)
       end
 
+      def respond_to_missing?(method, include_private = false)
+        base_instance.respond_to?(method, include_private)
+      end
+
+      def method_missing(method, *args, &block)
+        # If there's a missing method, it may be defined on the base_instance instead.
+        if respond_to_missing?(method)
+          base_instance.send(method, *args, &block)
+        else
+          super
+        end
+      end
+
       private
 
       # Adds a new stage to the set up require to get a Grape::API up and running

spec/grape/api_spec.rb

@@ -3209,6 +3209,43 @@ def static
           expect { a.mount b }.to_not raise_error
         end
       end
+
+      context 'when including a module' do
+        let(:included_module) do
+          Module.new do
+            def self.included(base)
+              base.extend(ClassMethods)
+            end
+            module ClassMethods
+              def my_method
+                @test = true
+              end
+            end
+          end
+        end
+
+        it 'should correctly include module in nested mount' do
+          module_to_include = included_module
+          v1 = Class.new(Grape::API) do
+            version :v1, using: :path
+            include module_to_include
+            my_method
+          end
+          v2 = Class.new(Grape::API) do
+            version :v2, using: :path
+          end
+          segment_base = Class.new(Grape::API) do
+            mount v1
+            mount v2
+          end
+
+          Class.new(Grape::API) do
+            mount segment_base
+          end
+
+          expect(v1.my_method).to be_truthy
+        end
+      end
     end
   end