scope_leak.rb

# Activate the gem you are reporting the issue against.
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 :posts do |t|
    t.string :title
  end
end

class Post < ActiveRecord::Base
  def self.total_post_count
    Post.count
  end
end

class BugTest < Minitest::Test
  def test_scope_leak
    Post.create! title: "one"
    Post.create! title: "two"
    Post.create! title: "three"

    assert_equal 3, Post.total_post_count
    assert_equal 3, Post.where(title: "one").total_post_count
  end
end

Fails with:

  1) Failure:
BugTest#test_scope_leak [bug.rb:29]:
Expected: 3
  Actual: 1

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

the relevant SQL is:

D, [2013-09-03T17:36:00.071743 #33892] DEBUG -- :    (0.1ms)  SELECT COUNT(*) FROM "posts"
D, [2013-09-03T17:36:00.083370 #33892] DEBUG -- :    (0.1ms)  SELECT COUNT(*) FROM "posts"  WHERE "posts"."title" = 'one'

Investigation related to https://meta.discourse.org/t/search-not-working-for-staff-users/11371/7