Linting `traits: true` on nested factories made from traits causes those traits to be called twice in one build

[Henry Blyth]

Description

Calling FactoryBot.lint([my_factory], traits: true) will create a factory with every trait it has defined.

For most factories and traits, this is fine. However, when a nested factory uses a trait, the trait is run twice: once in the definition of the factory, and again because the trait is passed in to the strategy call.

Reproduction Steps

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"
  git_source(:github) { |repo| "https://github.com/#{repo}.git" }
  gem "factory_bot", "~> 6.0"
  gem "activerecord"
  gem "sqlite3"
end

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

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :post_authors, force: true do |t|
    t.string :name
    t.integer :post_id
    t.index ["name", "post_id"], name: "index_post_author_unique", unique: true
  end
  create_table :posts, force: true do |t|
    t.string :title
    t.string :body
    t.boolean :approved
  end
  add_foreign_key "post_authors", "posts"
end

class PostAuthor < ActiveRecord::Base
  belongs_to :post
end

class Post < ActiveRecord::Base
  has_many :post_authors
end

FactoryBot.define do
  factory :post_author # has a unique index on post_id and name

  factory :post do
    title { "A title" }

    trait :with_authors do
      transient do
        author_names { ['Björn', 'Benny', 'Agnetha', 'Frida'] }
      end

      after(:create) do |post, evaluator|
        # Running this twice will cause an index violation.
        evaluator.author_names.each { |name| create(:post_author, post: post, name: name) }
      end
    end

    factory :approved_post do
      with_authors

      approved { true }
    end
  end
end

# Override strategy method so we can see what happens under the hood.
module FactoryBot
  def self.create(*args, **kwargs)
    puts "calling create with args: #{args} and kwargs: #{kwargs}"
    super
  end
end

class FactoryBotTest < Minitest::Test
  def test_factory_bot_lint
    FactoryBot.factories.each do |factory|
      puts "Lint #{factory.name}"
      ActiveRecord::Base.transaction do
        FactoryBot.lint([factory]) # passes
        raise ActiveRecord::Rollback
      end
    end
  end

  def test_factory_bot_lint_with_traits
    FactoryBot.factories.each do |factory|
      puts "Lint #{factory.name} with traits"
      ActiveRecord::Base.transaction do
        FactoryBot.lint([factory], traits: true) # fails for approved_post
        raise ActiveRecord::Rollback
      end
    end
  end
end

# Run the tests with `ruby <filename>`

Expected behavior

Factories defined with traits from parent factories should not be linted with those traits. This is the same as saying the following:

create(:post, :with_author_names) # this is fine
create(:approved_post) # this is also fine

# One would refrain from doing this, but calling it shouldn't double up the `:with_author_names` trait.
create(:post, :with_author_names, :with_author_names)

# Knowledge of the app being developed would cause one to refrain against this, but calling it shouldn't
# double up the `:with_author_names` trait.
create(:approved_post, :with_author_names)

All tests pass. The only create calls that are logged are:

calling create with args: [:post_author] and kwargs: {}
calling create with args: [:post] and kwargs: {}
calling create with args: [:post, "with_authors"] and kwargs: {}
calling create with args: [:approved_post] and kwargs: {}

Actual behavior

One test fails:

Finished in 0.009972s, 200.5616 runs/s, 0.0000 assertions/s.

  1) Error:
FactoryBotTest#test_factory_bot_lint_with_traits:
FactoryBot::InvalidFactoryError: The following factories are invalid:

* approved_post+with_authors - SQLite3::ConstraintException: UNIQUE constraint failed: post_authors.name, post_authors.post_id (ActiveRecord::RecordNotUnique)
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/factory_bot-6.2.1/lib/factory_bot/linter.rb:13:in `lint!'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/factory_bot-6.2.1/lib/factory_bot.rb:70:in `lint'
    factory_bot_test.rb:89:in `block (2 levels) in test_factory_bot_lint_with_traits'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/activerecord-6.1.7/lib/active_record/connection_adapters/abstract/database_statements.rb:320:in `block in transaction'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/activerecord-6.1.7/lib/active_record/connection_adapters/abstract/transaction.rb:319:in `block in within_new_transaction'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/activesupport-6.1.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb:26:in `block (2 levels) in synchronize'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/activesupport-6.1.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb:25:in `handle_interrupt'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/activesupport-6.1.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb:25:in `block in synchronize'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/activesupport-6.1.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb:21:in `handle_interrupt'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/activesupport-6.1.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb:21:in `synchronize'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/activerecord-6.1.7/lib/active_record/connection_adapters/abstract/transaction.rb:317:in `within_new_transaction'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/activerecord-6.1.7/lib/active_record/connection_adapters/abstract/database_statements.rb:320:in `transaction'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/activerecord-6.1.7/lib/active_record/transactions.rb:209:in `transaction'
    factory_bot_test.rb:88:in `block in test_factory_bot_lint_with_traits'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/factory_bot-6.2.1/lib/factory_bot/registry.rb:19:in `each'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/factory_bot-6.2.1/lib/factory_bot/registry.rb:19:in `each'
    /Users/henry/.rbenv/versions/2.6.10/gemsets/bookwhen_admin/gems/factory_bot-6.2.1/lib/factory_bot/decorator.rb:21:in `method_missing'
    factory_bot_test.rb:86:in `test_factory_bot_lint_with_traits'

2 runs, 0 assertions, 0 failures, 1 errors, 0 skips

The incorrect create call that was logged is:

calling create with args: [:approved_post, "with_authors"] and kwargs: {}

System configuration

factory_bot version: 6.0.2 (tested on latest 6.2.1 as bundler inline downloaded "~6.0")
rails version: 6.0.5.1
ruby version: 2.6.10