MONGOID-5664 [Monkey Patch Removal] Remove Object#__setter__ monkey-patch (#5707)

* Remove Object#__setter__ monkey-patch. This is a trivial method so I've just inlined it. (It was already inlined in several other places.)

* deprecate __setter__ instead of removing it

---------

Co-authored-by: Jamis Buck <[email protected]>

Author: johnnyshields

lib/mongoid/association/relatable.rb

@@ -81,7 +81,7 @@ def get_callbacks(callback_type)
       #
       # @return [ String ] The type setter method.
       def type_setter
-        @type_setter ||= type.__setter__
+        @type_setter ||= "#{type}=" if type
       end
 
       # Whether trying to bind an object using this association should raise
@@ -233,7 +233,7 @@ def path(document)
       #
       # @return [ String ] The name of the setter.
       def inverse_type_setter
-        @inverse_type_setter ||= inverse_type.__setter__
+        @inverse_type_setter ||= "#{inverse_type}=" if inverse_type
       end
 
       # Get the name of the method to check if the foreign key has changed.

lib/mongoid/extensions/nil_class.rb

@@ -3,19 +3,19 @@
 
 module Mongoid
   module Extensions
-
     # Adds type-casting behavior to NilClass.
     module NilClass
-
       # Try to form a setter from this object.
       #
       # @example Try to form a setter.
       #   object.__setter__
       #
       # @return [ nil ] Always nil.
+      # @deprecated
       def __setter__
         self
       end
+      Mongoid.deprecate(self, :__setter__)
 
       # Get the name of a nil collection.
       #
@@ -30,4 +30,4 @@ def collectionize
   end
 end
 
-::NilClass.__send__(:include, Mongoid::Extensions::NilClass)
+NilClass.include Mongoid::Extensions::NilClass

lib/mongoid/extensions/object.rb

@@ -50,9 +50,11 @@ def __mongoize_time__
       #   object.__setter__
       #
       # @return [ String ] The object as a string plus =.
+      # @deprecated
       def __setter__
         "#{self}="
       end
+      Mongoid.deprecate(self, :__setter__)
 
       # Get the value of the object as a mongo friendly sort value.
       #