Ensure that inverse associations are set before running callbacks

If a parent association was accessed in an `after_find` or
`after_initialize` callback, it would always end up loading the
association, and then immediately overwriting the association we just
loaded. If this occurred in a way that the parent's `current_scope` was
set to eager load the child, this would result in an infinite loop and
eventually overflow the stack.

For records that are created with `.new`, we have a mechanism to
perform an action before the callbacks are run. I've introduced the same
code path for records created with `instantiate`, and updated all code
which sets inverse instances on newly loaded associations to use this
block instead.

Fixes #26320.

1 files changed, 4 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/association_relation.rb b/activerecord/lib/active_record/association_relation.rb
index 2da2d968b9..de2d03cd0b 100644
--- a/activerecord/lib/active_record/association_relation.rb
+++ b/activerecord/lib/active_record/association_relation.rb
@@ -29,7 +29,10 @@ module ActiveRecord
     private
 
       def exec_queries
-        super.each { |r| @association.set_inverse_instance r }
+        super do |r|
+          @association.set_inverse_instance r
+          yield r if block_given?
+        end
       end
   end
 end