find_by_id causes stack overflow in after_find callback

[johnnaegle]

Steps to reproduce

An executable test case is below. It demonstrates that find_by_id behaves differently than find(id), where(:id => id).first, and find_by(:id => id). find_by_id is raising a SystemStackError when including has_many relationships and that relationship has an after_find callback that access the parent object.

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"
  gem "rails", github: "rails/rails"
  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 :foods, force: true do |t|
  end

  create_table :measurements, force: true do |t|
    t.integer :food_id
    t.string :name
    t.boolean :default
  end
end

class Food < ActiveRecord::Base
  has_many :measurements, :inverse_of => :food
end

class Measurement < ActiveRecord::Base
  belongs_to :food, :inverse_of => :measurements

  after_find do
    puts "Triggered after find"
    self.name = 'serving' if name.blank? && default? && food.present?
  end
end

class BugTest < Minitest::Test
  def setup
    @food = Food.create!
    @measurement = @food.measurements.create!(:default => true)
  end

  def test_find_does_not_stack_overflow
    Food.includes(:measurements).find(@food.id)
  end

  def test_where_does_not_stack_overflow
    Food.includes(:measurements).where(:id => @food.id).first
  end

  def test_find_by_does_not_stack_overflow
    Food.includes(:measurements).find_by(:id => @food.id)
  end

  def test_find_by_id_does_not_stack_overflow
    Food.find_by_id(@food.id)
  end

  def test_find_by_id_with_joins_does_not_stack_overflow
    Food.joins(:measurements).find_by_id(@food.id)
  end

  def test_find_by_id_with_includes_does_not_stack_overflow
    begin
      Food.includes(:measurements).find_by_id(@food.id)
    rescue SystemStackError => e
      raise "find_by_id with includes produced a stack overflow"
    end
  end

  def test_find_by_id_with_joins_and_includes_does_not_stack_overflow
    begin
      Food.joins(:measurements).includes(:measurements).find_by_id(@food.id)
    rescue SystemStackError => e
      raise "find_by_id with includes and joins produced a stack overflow"
    end
  end
end

This test fails with:

Finished in 1.063656s, 6.5811 runs/s, 0.0000 assertions/s.

  1) Error:
BugTest#test_find_by_id_with_joins_and_includes_does_not_stack_overflow:
RuntimeError: find_by_id with includes and joins produced a stack overflow
    wtfrails.rb:84:in `rescue in test_find_by_id_with_joins_and_includes_does_not_stack_overflow'
    wtfrails.rb:81:in `test_find_by_id_with_joins_and_includes_does_not_stack_overflow'


  2) Error:
BugTest#test_find_by_id_with_includes_does_not_stack_overflow:
RuntimeError: find_by_id with includes produced a stack overflow
    wtfrails.rb:76:in `rescue in test_find_by_id_with_includes_does_not_stack_overflow'
    wtfrails.rb:73:in `test_find_by_id_with_includes_does_not_stack_overflow'

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

Expected behavior

find_by_id, where(:id => id).first, find_by(:id => id) and find should all have the same callback behavior. They should not raise SystemStackError

Actual behavior

SystemStackError is raised.

System configuration

Rails version:

• activerecord 5.1.0.alpha
• activerecord 4.2.6

Ruby version:

• ruby 2.3.1p112