Avoid warning when loading YAMLColumn generated by old versions of Rails on Ruby 2.7

Author: rafaelfranca

activerecord/lib/active_record/coders/yaml_column.rb

@@ -15,6 +15,17 @@ def initialize(attr_name, object_class = Object, permitted_classes: [], unsafe_l
         check_arity_of_constructor
       end
 
+      def init_with(coder) # :nodoc:
+        # This is just to avoid the warning about trying to use instance variables before defining them
+        # when loading from an YAML generated in a Rails version before 7.1.
+        #
+        # This method can be removed when we drop support to Ruby 2.7.
+        @attr_name = coder["attr_name"]
+        @object_class = coder["object_class"]
+        @permitted_classes = coder["permitted_classes"] || []
+        @unsafe_load = coder["unsafe_load"]
+      end
+
       def dump(obj)
         return if obj.nil?
 
@@ -42,11 +53,23 @@ def assert_valid_value(obj, action:)
 
       private
         def permitted_classes
-          [*ActiveRecord.yaml_column_permitted_classes, *@permitted_classes]
+          # This `defined?` check is just to avoid the warning about trying to use instance variables before defining
+          # them when loading from an Marshal object generated in a Rails version before 7.1.
+          #
+          # The `defined?` can be removed when we drop support to Ruby 2.7.
+          if defined?(@permitted_classes)
+            ActiveRecord.yaml_column_permitted_classes + @permitted_classes
+          else
+            ActiveRecord.yaml_column_permitted_classes
+          end
         end
 
         def unsafe_load?
-          @unsafe_load.nil? ? ActiveRecord.use_yaml_unsafe_load : @unsafe_load
+          # This `defined?` check is just to avoid the warning about trying to use instance variables before defining
+          # them when loading from an Marshal object generated in a Rails version before 7.1.
+          #
+          # The `defined?` can be removed when we drop support to Ruby 2.7.
+          defined?(@unsafe_load) && !@unsafe_load.nil? ? @unsafe_load : ActiveRecord.use_yaml_unsafe_load
         end
 
         def check_arity_of_constructor