Always assume strings with non-numeric characters change numeric types

We previously only did this if the old value was zero, to make sure
numericality validations run and failed if the user gave 'wibble' as the
value, which would be type cast to 0. However, numericality validations
will fail if there are any non-numeric characters in the string, so 5 ->
'5wibble' should also be marked as changed.

activerecord/CHANGELOG.md

@@ -1,3 +1,17 @@
+*   Assume numeric types have changed if they were assigned to a value that
+    would fail numericality validation, regardless of the old value. Previously
+    this would only occur if the old value was 0.
+
+    Example:
+
+        model = Model.create!(number: 5)
+        model.number = '5wibble'
+        model.number_changed? # => true
+
+    Fixes #14731.
+
+    *Sean Griffin*
+
 *   `reload` no longer merges with the existing attributes.
     The attribute hash is fully replaced. The record is put into the same state
     as it would be with `Model.find(model.id)`.

activerecord/lib/active_record/type/numeric.rb

@@ -16,13 +16,13 @@ def type_cast(value)
       end
 
       def changed?(old_value, _new_value, new_value_before_type_cast) # :nodoc:
-        super || zero_to_non_number?(old_value, new_value_before_type_cast)
+        super || number_to_non_number?(old_value, new_value_before_type_cast)
       end
 
       private
 
-      def zero_to_non_number?(old_value, new_value_before_type_cast)
-        old_value == 0 && non_numeric_string?(new_value_before_type_cast)
+      def number_to_non_number?(old_value, new_value_before_type_cast)
+        old_value != nil && non_numeric_string?(new_value_before_type_cast)
       end
 
       def non_numeric_string?(value)

activerecord/test/cases/types_test.rb

@@ -79,11 +79,29 @@ def test_type_cast_nan_and_infinity_to_integer
         assert_nil type.type_cast_from_user(1.0/0.0)
       end
 
+      def test_changing_integers
+        type = Type::Integer.new
+
+        assert type.changed?(5, 5, '5wibble')
+        assert_not type.changed?(5, 5, '5')
+        assert_not type.changed?(5, 5, '5.0')
+        assert_not type.changed?(nil, nil, nil)
+      end
+
       def test_type_cast_float
         type = Type::Float.new
         assert_equal 1.0, type.type_cast_from_user("1")
       end
 
+      def test_changing_float
+        type = Type::Float.new
+
+        assert type.changed?(5.0, 5.0, '5wibble')
+        assert_not type.changed?(5.0, 5.0, '5')
+        assert_not type.changed?(5.0, 5.0, '5.0')
+        assert_not type.changed?(nil, nil, nil)
+      end
+
       def test_type_cast_decimal
         type = Type::Decimal.new
         assert_equal BigDecimal.new("0"), type.type_cast_from_user(BigDecimal.new("0"))