Generate delegation methods to named scope in the definition time

The delegation methods to named scope are defined when `method_missing`
is invoked on the relation.

Since #29301, the receiver in the named scope is changed to the relation
like others (e.g. `default_scope`, etc) for consistency.

Most named scopes would be delegated from relation by `method_missing`,
since we don't allow scopes to be defined which conflict with instance
methods on `Relation` (#31179). But if a named scope is defined with the
same name as any method on the `superclass` (e.g. `Kernel.open`), the
`method_missing` on the relation is not invoked.

To address the issue, make the delegation methods to named scope is
generated in the definition time.

Fixes #34098.

2 files changed, 32 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/relation/delegation.rb b/activerecord/lib/active_record/relation/delegation.rb
index 8f657840f5..383dc1bf4b 100644
--- a/activerecord/lib/active_record/relation/delegation.rb
+++ b/activerecord/lib/active_record/relation/delegation.rb
@@ -17,6 +17,7 @@ module ActiveRecord
           delegate = Class.new(klass) {
             include ClassSpecificRelation
           }
+          include_relation_methods(delegate)
           mangled_name = klass.name.gsub("::", "_")
           const_set mangled_name, delegate
           private_constant mangled_name
@@ -29,6 +30,35 @@ module ActiveRecord
         child_class.initialize_relation_delegate_cache
         super
       end
+
+      protected
+        def include_relation_methods(delegate)
+          superclass.include_relation_methods(delegate) unless base_class?
+          delegate.include generated_relation_methods
+        end
+
+      private
+        def generated_relation_methods
+          @generated_relation_methods ||= Module.new.tap do |mod|
+            mod_name = "GeneratedRelationMethods"
+            const_set mod_name, mod
+            private_constant mod_name
+          end
+        end
+
+        def generate_relation_method(method)
+          if /\A[a-zA-Z_]\w*[!?]?\z/.match?(method)
+            generated_relation_methods.module_eval <<-RUBY, __FILE__, __LINE__ + 1
+              def #{method}(*args, &block)
+                scoping { klass.#{method}(*args, &block) }
+              end
+            RUBY
+          else
+            generated_relation_methods.send(:define_method, method) do |*args, &block|
+              scoping { klass.public_send(method, *args, &block) }
+            end
+          end
+        end
     end
 
     extend ActiveSupport::Concern
diff --git a/activerecord/lib/active_record/scoping/named.rb b/activerecord/lib/active_record/scoping/named.rb
index 573d97b819..d5cc5db97e 100644
--- a/activerecord/lib/active_record/scoping/named.rb
+++ b/activerecord/lib/active_record/scoping/named.rb
@@ -191,6 +191,8 @@ module ActiveRecord
               scope
             end
           end
+
+          generate_relation_method(name)
         end
 
         private