attribute_changed? returns true when assigning a float to a BigDecimal

[matiasgarcia]

Steps to reproduce

# frozen_string_literal: true

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"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  # Activate the gem you are reporting the issue against.
  gem "activerecord", "5.1.4"
  gem "sqlite3"
end

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

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# 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 :prices, force: true do |t|
    t.decimal :amount, precision: 63, scale: 30
  end
end

class Price < ActiveRecord::Base

end

class BugTest < Minitest::Test
  def test_big_decimal_change
    amount = 0.00005
    price = Price.create!(amount: amount)
    price.amount = amount
    assert_equal false, price.attribute_changed?(:amount)
  end

  def test_previous_value_and_new_value
    amount = 0.00005
    price = Price.create!(amount: amount)
    price.amount = amount
    previous_value, new_value = price.changes[:amount]
    refute_equal previous_value, new_value
  end
end

Result of running this:

  1) Failure:
BugTest#test_big_decimal_change [test.rb:46]:
Expected: false
  Actual: true

  2) Failure:
BugTest#test_previous_value_and_new_value [test.rb:54]:
Expected 0.5e-4 to not be equal to 0.5e-4.

Expected behavior

attribute_changed?(:amount) should return false.

Actual behavior

attribute_changed?(:amount) returns true despite previous value and new_value are the same.

System configuration

Rails version: 5.1.4

Ruby version: 2.4.1

[yskkin]

diff --git a/activemodel/lib/active_model/type/helpers/numeric.rb b/activemodel/lib/active_model/type/helpers/numeric.rb
index 16e14f9e5f..724dc06d2d 100644
--- a/activemodel/lib/active_model/type/helpers/numeric.rb
+++ b/activemodel/lib/active_model/type/helpers/numeric.rb
@@ -29,7 +29,7 @@ def non_numeric_string?(value)
             # 'wibble'.to_i will give zero, we want to make sure
             # that we aren't marking int zero to string zero as
             # changed.
-            value.to_s !~ /\A-?\d+\.?\d*\z/
+            value.to_s !~ /\A-?\d+\.?\d*(e[-+]\d+)?\z/
           end
       end
     end

This seems to fix the issue.

[matiasgarcia]

That fix makes sense I guess. Hope it's merged soon.