Support kwargs for named scopes

[jhawthorn]

Previously Ruby 2.7 would generate a warning when trying to define a named scope which took keyword arguments.

class Books
  scope :with_attributes, -> (author: nil, title: nil) {
    # ...
  }
end

This should allow those scopes to be defined and run without warnings.

cc @eileencodes @kytrinyx @HParker

[kamipo]

Can you use singleton_class.send(:ruby2_keywords, name) if respond_to?(:ruby2_keywords, true)?

diff --git a/activerecord/lib/active_record/scoping/named.rb b/activerecord/lib/active_record/scoping/named.rb
index e2167881e5..8ffdadae54 100644
--- a/activerecord/lib/active_record/scoping/named.rb
+++ b/activerecord/lib/active_record/scoping/named.rb
@@ -195,6 +195,7 @@ def scope(name, body, &block)
               scope
             end
           end
+          singleton_class.send(:ruby2_keywords, name) if respond_to?(:ruby2_keywords, true)
 
           generate_relation_method(name)
         end

Strictly speaking, *args to *args, **kwargs is not perfectly compatible except Ruby 3.0, ruby2_keywords is only way to do that as long as support Ruby 2.x.

[jhawthorn]

Seems like ruby2_keywords is only valid for methods taking kwargs or a splat.

named.rb:198: warning: Skipping set of ruby2_keywords flag for tagged_with (method accepts keywords or method does not accept argument splat)

I also wanted to avoid this because we should see warnings in 2.7 if a named scope takes kwargs but is passed a hash.

A agree that the *args, **kwargs doesn't quite work here. It might be that the only way to do this is using some if RUBY_VERSION >= checks and duplicating these two methods 😩

[kamipo]

I've added test case for generate_relation_method 7ce3451, it also demonstrates a regression for this PR.

Can you apply the above patch singleton_class.send(:ruby2_keywords, name) if respond_to?(:ruby2_keywords, true) in lib/active_record/scoping/named.rb instead of this PR? That patch is only way to pass 7ce3451 and address kwargs warnings in Ruby 2.7.

[jhawthorn]

Per my last comment we can't use that here as it causes even more warnings.

[jhawthorn]

Closed for #39199