Add tests ensuring CurrentAttributes eagerly define class methods

activesupport/lib/active_support/current_attributes.rb

@@ -117,6 +117,9 @@ def attribute(*names, default: NOT_SET)
           raise ArgumentError, "Restricted attribute names: #{invalid_attribute_names.join(", ")}"
         end
 
+        Delegation.generate(singleton_class, names, to: :instance, nilable: false, signature: "")
+        Delegation.generate(singleton_class, names.map { |n| "#{n}=" }, to: :instance, nilable: false, signature: "value")
+
         ActiveSupport::CodeGenerator.batch(generated_attribute_methods, __FILE__, __LINE__) do |owner|
           names.each do |name|
             owner.define_cached_method(name, namespace: :current_attributes) do |batch|
@@ -134,9 +137,6 @@ def attribute(*names, default: NOT_SET)
           end
         end
 
-        Delegation.generate(singleton_class, names, to: :instance, nilable: false, signature: "")
-        Delegation.generate(singleton_class, names.map { |n| "#{n}=" }, to: :instance, nilable: false, signature: "value")
-
         self.defaults = defaults.merge(names.index_with { default })
       end
 
@@ -185,9 +185,16 @@ def respond_to_missing?(name, _)
 
         def method_added(name)
           super
+
+          # We try to generate instance delegators early to not rely on method_missing.
           return if name == :initialize
+
+          # If the added method isn't public, we don't delegate it.
           return unless public_method_defined?(name)
+
+          # If we already have a class method by that name, we don't override it.
           return if singleton_class.method_defined?(name) || singleton_class.private_method_defined?(name)
+
           Delegation.generate(singleton_class, [name], to: :instance, as: self, nilable: false)
         end
     end

activesupport/test/current_attributes_test.rb

@@ -276,4 +276,35 @@ def foo; end # Sets the cache because of a `method_added` hook
 
     assert_instance_of(Hash, current.bar)
   end
+
+  test "instance delegators are eagerly defined" do
+    current = Class.new(ActiveSupport::CurrentAttributes) do
+      def self.name
+        "MyCurrent"
+      end
+
+      def regular
+        :regular
+      end
+
+      attribute :attr, default: :att
+    end
+
+    assert current.singleton_class.method_defined?(:attr)
+    assert current.singleton_class.method_defined?(:attr=)
+    assert current.singleton_class.method_defined?(:regular)
+  end
+
+  test "attribute delegators have precise signature" do
+    current = Class.new(ActiveSupport::CurrentAttributes) do
+      def self.name
+        "MyCurrent"
+      end
+
+      attribute :attr, default: :att
+    end
+
+    assert_equal [], current.method(:attr).parameters
+    assert_equal [[:req, :value]], current.method(:attr=).parameters
+  end
 end