Raise `RecordNotDestroyed` when children can't be replaced

Fixes #12812
Raise `ActiveRecord::RecordNotDestroyed` when a child marked with
`dependent: destroy` can't be destroyed.

The following code:
```ruby
class Post < ActiveRecord::Base
  has_many :comments, dependent: :destroy
end

class Comment < ActiveRecord::Base
  before_destroy do
    return false
  end
end

post = Post.create!(comments: [Comment.create!])
post.comments = [Comment.create!]
````

would result in a `post` with two `comments`.
With this commit, the same code would raise a `RecordNotDestroyed`
exception, keeping the `post` with the same `comment`.

1 files changed, 11 insertions, 0 deletions

diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index a025d49fa3..45bc974025 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -1770,4 +1770,15 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal [bulb1], car.bulbs
     assert_equal [bulb1, bulb2], car.all_bulbs.sort_by(&:id)
   end
+
+  test "raises RecordNotDestroyed when replaced child can't be destroyed" do
+    car = Car.create!
+    original_child = FailedBulb.create!(car: car)
+
+    assert_raise(ActiveRecord::RecordNotDestroyed) do
+      car.failed_bulbs = [FailedBulb.create!]
+    end
+
+    assert_equal [original_child], car.reload.failed_bulbs
+  end
 end