From d1df4c100fee09efe85acb6663bfebcfa7036485 Mon Sep 17 00:00:00 2001
From: Marcelo Lauxen <marcelolauxen16@gmail.com>
Date: Wed, 21 Jul 2021 08:45:09 -0300
Subject: [PATCH] Fix dirty check for Float::NaN and BigDecimal::NaN

Float::NaN and BigDecimal::NaN in Ruby are [special values](https://bugs.ruby-lang.org/issues/1720) and can't be compared with `==`.
---
 activemodel/CHANGELOG.md                             |  7 +++++++
 activemodel/lib/active_model/type/helpers/numeric.rb | 10 +++++++++-
 activemodel/test/cases/type/decimal_test.rb          |  2 ++
 activemodel/test/cases/type/float_test.rb            |  2 ++
 4 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/activemodel/CHANGELOG.md b/activemodel/CHANGELOG.md
index 0659793575..9138bcabad 100644
--- a/activemodel/CHANGELOG.md
+++ b/activemodel/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Fix dirty check for Float::NaN and BigDecimal::NaN.
+
+    Float::NaN and BigDecimal::NaN in Ruby are [special values](https://bugs.ruby-lang.org/issues/1720) 
+    and can't be compared with `==`.
+
+    *Marcelo Lauxen*
+
 *   Fix `to_json` for `ActiveModel::Dirty` object.
 
     Exclude `mutations_from_database` attribute from json as it lead to recursion.
diff --git a/activemodel/lib/active_model/type/helpers/numeric.rb b/activemodel/lib/active_model/type/helpers/numeric.rb
index 5b1db1f36b..7a5c0e681e 100644
--- a/activemodel/lib/active_model/type/helpers/numeric.rb
+++ b/activemodel/lib/active_model/type/helpers/numeric.rb
@@ -25,10 +25,18 @@ module ActiveModel
         end
 
         def changed?(old_value, _new_value, new_value_before_type_cast) # :nodoc:
-          super || number_to_non_number?(old_value, new_value_before_type_cast)
+          (super || number_to_non_number?(old_value, new_value_before_type_cast)) &&
+            !equal_nan?(old_value, new_value_before_type_cast)
         end
 
         private
+          def equal_nan?(old_value, new_value)
+            (old_value.is_a?(::Float) || old_value.is_a?(BigDecimal)) &&
+              old_value.nan? &&
+              old_value.instance_of?(new_value.class) &&
+              new_value.nan?
+          end
+
           def number_to_non_number?(old_value, new_value_before_type_cast)
             old_value != nil && non_numeric_string?(new_value_before_type_cast.to_s)
           end
diff --git a/activemodel/test/cases/type/decimal_test.rb b/activemodel/test/cases/type/decimal_test.rb
index 38941ba8b5..384bae1d90 100644
--- a/activemodel/test/cases/type/decimal_test.rb
+++ b/activemodel/test/cases/type/decimal_test.rb
@@ -66,6 +66,8 @@ module ActiveModel
         assert_not type.changed?(5.0, 5.0, "5.0")
         assert_not type.changed?(-5.0, -5.0, "-5.0")
         assert_not type.changed?(5.0, 5.0, "0.5e+1")
+        assert_not type.changed?(BigDecimal("0.0") / 0, BigDecimal("0.0") / 0, BigDecimal("0.0") / 0)
+        assert type.changed?(BigDecimal("0.0") / 0, 0.0 / 0.0, 0.0 / 0.0)
       end
 
       def test_scale_is_applied_before_precision_to_prevent_rounding_errors
diff --git a/activemodel/test/cases/type/float_test.rb b/activemodel/test/cases/type/float_test.rb
index 230a8dda32..ca18e125d2 100644
--- a/activemodel/test/cases/type/float_test.rb
+++ b/activemodel/test/cases/type/float_test.rb
@@ -28,6 +28,8 @@ module ActiveModel
         assert_not type.changed?(5.0, 5.0, "5.0")
         assert_not type.changed?(500.0, 500.0, "0.5E+4")
         assert_not type.changed?(nil, nil, nil)
+        assert_not type.changed?(0.0 / 0.0, 0.0 / 0.0, 0.0 / 0.0)
+        assert type.changed?(0.0 / 0.0, BigDecimal("0.0") / 0, BigDecimal("0.0") / 0)
       end
     end
   end