Rails/FindByOrAssignmentMemoization autocorrect behavior leads to unintuitive test failures

[liangmicha]

In our codebase, we have some code that like this:

def user =  @user ||= User.find_by(id: params.require("user_id"))

This code currently fails the Rails/FindByOrAssignmentMemoization rubocop rule.

Expected behavior

I expect that running rubocop -A will lead to changes that make sense, i.e the following, per the
rails style guide

  def user
      return @user if defined?(@user)

      @user = User.find_by(id: params.require("user_id"))
    end

Actual behavior

Instead, the result is:

    if defined?(@user)
      attr_reader :user
    end

    @user = User.find_by(id: params.require("user_id"))

This leads to a really difficult to understand issue when running bundle exec rspec for any tests on circleCI (but rspec works locally):

An error occurred while loading ./spec/services/recover_care_pathway_answers_spec.rb.
Failure/Error: require File.expand_path("../config/environment", __dir__)

FrozenError:
  can't modify frozen Array: ["/home/circleci/project/lib", "/home/circleci/project/app/channels", "/home/circleci/project/app/components", "/home/circleci/project/app/concerns", "/home/circleci/project/app/config", "/home/circleci/project/app/controllers", "/home/circleci/project/app/dashboards", "/home/circleci/project/app/fields", "/home/circleci/project/app/helpers", "/home/circleci/project/app/jobs", "/home/circleci/project/app/mailers", "/home/circleci/project/app/middleware", "/home/circleci/project/app/models", "/home/circleci/project/app/policies", "/home/circleci/project/app/revocation_strategies", "/home/circleci/project/app/serializers", "/home/circleci/project/app/services", "/home/circleci/project/app/validators", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/solid_cache-1.0.7/app/jobs", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/solid_cache-1.0.7/app/models", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/devise-4.9.4/app/controllers", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/devise-4.9.4/app/helpers", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/devise-4.9.4/app/mailers", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/administrate-0.20.1/app/controllers", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/administrate-0.20.1/app/controllers/concerns", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/administrate-0.20.1/app/helpers", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/activestorage-7.2.2.1/app/controllers", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/activestorage-7.2.2.1/app/controllers/concerns", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/activestorage-7.2.2.1/app/jobs", "/home/circleci/project/vendor/bundle/ruby/3.4.0/gems/activestorage-7.2.2.1/app/models"]

$ rubocop -A --debug
For /Users/m/<redacted>/backend: configuration from /Users/m/<redacted>/backend/.rubocop.yml
Default configuration from /Users/m/.rbenv/versions/3.4.2/lib/ruby/gems/3.4.0/gems/rubocop-1.80.2/config/default.yml
Plugin configuration from /Users/m/.rbenv/versions/3.4.2/lib/ruby/gems/3.4.0/gems/rubocop-rails-2.33.3/config/default.yml
Plugin configuration from /Users/m/.rbenv/versions/3.4.2/lib/ruby/gems/3.4.0/gems/rubocop-rspec-3.7.0/config/default.yml
Plugin configuration from /Users/m/.rbenv/versions/3.4.2/lib/ruby/gems/3.4.0/gems/rubocop-rspec_rails-2.31.0/config/default.yml
Plugin configuration from /Users/m/.rbenv/versions/3.4.2/lib/ruby/gems/3.4.0/gems/rubocop-performance-1.26.0/config/default.yml
Plugin configuration from /Users/m/.rbenv/versions/3.4.2/lib/ruby/gems/3.4.0/gems/rubocop-capybara-2.22.1/config/default.yml
Plugin configuration from /Users/m/.rbenv/versions/3.4.2/lib/ruby/gems/3.4.0/gems/rubocop-factory_bot-2.27.1/config/default.yml
Inheriting configuration from /Users/m/<redacted>/backend/.rubocop_todo.yml
Use parallel by default.
Running parallel inspection

Offenses:

app/controllers/admin/dashboard_role_creation_codes_controller.rb:35:5: C: [Corrected] Style/AmbiguousEndlessMethodDefinition: Avoid using if statements with endless methods.
    def user = return @user if defined?(@user)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:35:5: C: [Corrected] Style/MultilineIfModifier: Favor a normal if-statement over a modifier clause in a multiline statement.
    def user ...
    ^^^^^^^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:35:5: C: [Corrected] Style/TrivialAccessors: Use attr_reader to define trivial reader methods.
    def user
    ^^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:35:16: C: [Corrected] Rails/FindByOrAssignmentMemoization: Avoid memoizing find_by results with ||=.
    def user = @user ||= User.find_by(id: params.require("user_id"))
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:35:16: C: [Corrected] Style/RedundantReturn: Redundant return detected.
    def user = return @user if defined?(@user)
               ^^^^^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:36:3: C: [Corrected] Layout/IndentationWidth: Use 2 (not -2) spaces for indentation.
  return @user
  ^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:36:3: C: [Corrected] Style/RedundantReturn: Redundant return detected.
  return @user
  ^^^^^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:36:7: C: [Corrected] Style/TrivialAccessors: Use attr_reader to define trivial reader methods.
      def user
      ^^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:37:1: W: [Corrected] Layout/DefEndAlignment: end at 37, 0 is not aligned with def at 35, 4.
end if defined?(@user)
^^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:37:1: C: [Corrected] Layout/IndentationConsistency: Inconsistent indentation detected.
@user = User.find_by(id: params.require("user_id"))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:37:1: C: [Corrected] Layout/IndentationWidth: Use 2 (not -2) spaces for indentation.
@user = User.find_by(id: params.require("user_id"))
^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:39:3: C: [Corrected] Layout/IndentationWidth: Use 2 (not 6) spaces for indentation.
        @user = User.find_by(id: params.require("user_id"))
  ^^^^^^
app/controllers/admin/dashboard_role_creation_codes_controller.rb:39:9: C: [Corrected] Layout/IndentationConsistency: Inconsistent indentation detected.
        @user = User.find_by(id: params.require("user_id"))
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

3154 files inspected, 13 offenses detected, 13 offenses corrected
Finished in 1.0526759999920614 seconds

Steps to reproduce the problem

See above.

RuboCop version

1.80.2 (using Parser 3.3.9.0, Prism 1.4.0, rubocop-ast 1.46.0, analyzing as Ruby 3.4, running on ruby 3.4.2) [arm64-darwin24]
  - rubocop-rails 2.33.3
  - rubocop-rspec 3.7.0
  - rubocop-rspec_rails 2.31.0
  - rubocop-performance 1.26.0
  - rubocop-capybara 2.22.1
  - rubocop-factory_bot 2.27.1