Mix ActiveModel::AttributeAssignment into Base

By including the [ActiveModel::AttributeAssignment][], the `Base` class
can access the [assign_attributes][] method for bulk assignment of
attributes **without** saving them to the server (like through
`Base#update_attributes`).

```ruby
person = Person.new

person.id   # => nil
person.name # => nil

person.assign_attributes id: 1, name: "Matz"

person.id   # => 1
person.name # => "Matz"
```

Support for versions prior to 7.2.0
---

This commit includes a conditional monkey-patch of the
`_assign_attribute` method when Active Model's version is < 7.2.0:

```ruby
  # 7.1.5.2
  def _assign_attribute(k, v)
    setter = :"#{k}="
    if respond_to?(setter)
      public_send(setter, v)
    else
      raise UnknownAttributeError.new(self, k.to_s)
    end
  end

  # 7.2.0
  def _assign_attribute(k, v)
    setter = :"#{k}="
    public_send(setter, v)
  rescue NoMethodError
    if respond_to?(setter)
      raise
    else
      raise UnknownAttributeError.new(self, k.to_s)
    end
  end
```

The change is necessary because the [7.1.5.2][] version queries the
instance with `respond_to?`, whereas the [7.2.0][] version skips the
query and sends the method first, falling back to a `NoMethodError`
rescue in case that it doesn't.

[#450][] is an alternative to including the monkey patch. If merged,
it'd make `respond_to?` behavior more like `method_missing`, so the
monkey patch would be unnecessary.

[ActiveModel::AttributeAssignment]: https://edgeapi.rubyonrails.org/classes/ActiveModel/AttributeAssignment.html
[assign_attributes]: https://edgeapi.rubyonrails.org/classes/ActiveModel/AttributeAssignment.html#method-i-assign_attributes
[7.1.5.2]: https://github.com/rails/rails/blob/v7.1.5.2/activemodel/lib/active_model/attribute_assignment.rb
[7.2.0]: https://github.com/rails/rails/blob/v7.2.0/activemodel/lib/active_model/attribute_assignment.rb
[#450]: #450

Author: seanpdoyle

lib/active_resource/base.rb

@@ -1589,7 +1589,7 @@ def load(attributes, remove_root = false, persisted = false)
       attributes = Formats.remove_root(attributes) if remove_root
 
       attributes.each do |key, value|
-        @attributes[key.to_s] =
+        assign_attributes key.to_s => (
           case value
           when Array
             resource = nil
@@ -1607,6 +1607,7 @@ def load(attributes, remove_root = false, persisted = false)
           else
             value.duplicable? ? value.dup : value
           end
+        )
       end
       self
     end
@@ -1827,6 +1828,19 @@ def method_missing(method_symbol, *arguments) # :nodoc:
           super
         end
       end
+
+      if ActiveModel::VERSION::MAJOR < 8 && ActiveModel::VERSION::MINOR < 2
+        def _assign_attribute(k, v)
+          setter = :"#{k}="
+          public_send(setter, v)
+        rescue NoMethodError
+          if respond_to?(setter)
+            raise
+          else
+            raise UnknownAttributeError.new(self, k.to_s)
+          end
+        end
+      end
   end
 
   class Base
@@ -1835,7 +1849,7 @@ class Base
     extend ActiveResource::Associations
 
     include Callbacks, CustomMethods, Validations, Serialization
-    include ActiveModel::Conversion
+    include ActiveModel::Conversion, ActiveModel::AttributeAssignment
     include ActiveModel::ForbiddenAttributesProtection
     include ActiveModel::Serializers::JSON
     include ActiveModel::Serializers::Xml

test/cases/base_test.rb

@@ -1179,6 +1179,15 @@ def test_complex_clone
     assert_not_equal matz.non_ar_hash, matz_c.non_ar_hash
   end
 
+  def test_assign_attributes
+    matz = Person.new
+
+    matz.assign_attributes "id" => 1, name: "Matz"
+
+    assert_equal 1, matz.id
+    assert_equal "Matz", matz.name
+  end
+
   def test_update
     matz = Person.find(:first)
     matz.name = "David"