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, 16 insertions, 5 deletions

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