`create_or_find_by` creates record when parent is not persisted

[jenshenny]

Steps to reproduce

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"
  gem "rails", github: "rails/rails", branch: "main"
  gem "sqlite3"
end

require "active_record"
require "minitest/autorun"
require "logger"

# This connection will do for database-independent bug reports
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :authors do |t|
    t.string :name
    t.timestamps
  end

  create_table :books do |t|
    t.string :name
    t.references :author
    t.timestamps
  end
end

class Author < ActiveRecord::Base
  has_many :books
end

class Book < ActiveRecord::Base
  belongs_to :author
end

class BugTest < Minitest::Test
  def test_find_or_create_by_with_destroyed_owner
    author = Author.create!(name: "Test Author")
    author.destroy!

    assert_raises(ActiveRecord::RecordNotSaved) do
      author.books.create_or_find_by!(name: "Test Book")
    end
  end
end

Expected behavior

A ActiveRecord::RecordNotSaved is raised with You cannot call create unless the parent is saved. I'd expect create_or_find_by to act like create and raise this error.

Actual behavior

The new record is created.

System configuration

Rails version:
Rails main since #54845

cc: @Edouard-chin

[Edouard-chin]

Thanks, I'll have a look