MONGOID-5232 Add Feature Flag: Bring Mongoid::Document's === implementation in alignment with Ruby behavior (#5142)

* MONGOID-5232 add feature flag

* MONGOID-5232 add config tests

* MONGOID-5232 add docs for feature flag

* MONGOID-5232 add note to docs about global flag

Author: neilshweky

source/reference/configuration.txt

@@ -296,6 +296,10 @@ for details on driver options.
       # existing method. (default: false)
       scope_overwrite_exception: false
 
+      # Corrects === behavior to be consistent with Ruby by only calling is_a?
+      # (default: false)
+      triple_equals_uses_is_a: false
+
       # In Mongoid 7.3.3 and earlier, when setting an embedded document, setting
       # it to nil, and then setting it again to that same original value, the
       # second update would not work and the value for the embedded document

source/release-notes/mongoid-7.4.txt

@@ -35,39 +35,45 @@ side with the left hand side as the argument:
 .. code-block:: ruby
 
   ModelClass === instance
-  
+
   # equivalent to:
   instance.is_a?(ModelClass)
 
 Previously, ``===`` returned ``true`` for some cases when the equivalent Ruby
 ``===`` implementation returned false.
 
+.. note::
+
+  In order to get this functionality, the ``Mongoid::triple_equals_uses_is_a``
+  global flag must be set to true. If it is set to false, the ``===`` operator
+  will function as it did in Mongoid 7.3.
+
 Mongoid 7.4 behavior:
 
 .. code-block:: ruby
 
   class Band
     include Mongoid::Document
   end
-  
+
   class CoverBand < Band
   end
-  
+
   band = Band.new
   cover_band = CoverBand.new
-  
+
   band === Band
   # => false
-  
+
   cover_band === Band
   # => false
-  
+
   Band === Band
   # => false
-  
+
   CoverBand === Band
   # => false
-  
+
 Mongoid 7.3 behavior:
 
 .. code-block:: ruby
@@ -77,10 +83,10 @@ Mongoid 7.3 behavior:
 
   cover_band === Band
   # => true
-  
+
   Band === Band
   # => true
-  
+
   CoverBand === Band
   # => true
 
@@ -92,7 +98,7 @@ and matches the core Ruby behavior:
 
   Band === band
   # => true
-  
+
   Band === cover_band
   # => true
 
@@ -132,11 +138,11 @@ documents, the aliases are now expanded. Given the following definitions:
     include Mongoid::Document
     embeds_many :managers
   end
-  
+
   class Manager
     include Mongoid::Document
     embedded_in :band
-    
+
     field :name, as: :n
   end