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.

6 files changed, 59 insertions, 5 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
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index eb65f9e74f..2d16815da8 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -2391,6 +2391,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   def test_collection_association_with_private_kernel_method
     firm = companies(:first_firm)
     assert_equal [accounts(:signals37)], firm.accounts.open
+    assert_equal [accounts(:signals37)], firm.accounts.available
   end
 
   def test_association_with_or_doesnt_set_inverse_instance_key
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 9914a61033..e471ee8039 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -1812,6 +1812,16 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal "Thank you for the welcome,Thank you again for the welcome", Post.first.comments.join(",")
   end
 
+  def test_relation_with_private_kernel_method
+    accounts = Account.all
+    assert_equal [accounts(:signals37)], accounts.open
+    assert_equal [accounts(:signals37)], accounts.available
+
+    sub_accounts = SubAccount.all
+    assert_equal [accounts(:signals37)], sub_accounts.open
+    assert_equal [accounts(:signals37)], sub_accounts.available
+  end
+
   test "#skip_query_cache!" do
     Post.cache do
       assert_queries(1) do
diff --git a/activerecord/test/models/account.rb b/activerecord/test/models/account.rb
index 0c3cd45a81..639e395743 100644
--- a/activerecord/test/models/account.rb
+++ b/activerecord/test/models/account.rb
@@ -11,9 +11,8 @@ class Account < ActiveRecord::Base
   end
 
   # Test private kernel method through collection proxy using has_many.
-  def self.open
-    where("firm_name = ?", "37signals")
-  end
+  scope :open, -> { where("firm_name = ?", "37signals") }
+  scope :available, -> { open }
 
   before_destroy do |account|
     if account.firm
@@ -32,3 +31,11 @@ class Account < ActiveRecord::Base
       "Sir, yes sir!"
     end
 end
+
+class SubAccount < Account
+  def self.instantiate_instance_of(klass, attributes, column_types = {}, &block)
+    klass = superclass
+    super
+  end
+  private_class_method :instantiate_instance_of
+end
diff --git a/activerecord/test/models/post.rb b/activerecord/test/models/post.rb
index 528585fb75..710a75ad30 100644
--- a/activerecord/test/models/post.rb
+++ b/activerecord/test/models/post.rb
@@ -297,8 +297,6 @@ end
 class FakeKlass
   extend ActiveRecord::Delegation::DelegateCache
 
-  inherited self
-
   class << self
     def connection
       Post.connection
@@ -335,5 +333,11 @@ class FakeKlass
     def predicate_builder
       Post.predicate_builder
     end
+
+    def base_class?
+      true
+    end
   end
+
+  inherited self
 end