Ensure numericality validations work with mutation

The detection of in-place changes caused a weird unexpected issue with
numericality validations. That validator (out of necessity) works on the
`_before_type_cast` version of the attribute, since on an `:integer`
type column, a non-numeric string would type cast to 0.

However, strings are mutable, and we changed strings to ensure that the
post type cast version of the attribute was a different instance than
the before type cast version (so the mutation detection can work
properly).

Even though strings are the only mutable type for which a numericality
validation makes sense, special casing strings would feel like a strange
change to make here. Instead, we can make the assumption that for all
mutable types, we should work on the post-type-cast version of the
attribute, since all cases which would return 0 for non-numeric strings
are immutable.

Fixes #17852

1 files changed, 13 insertions, 0 deletions

diff --git a/activerecord/test/cases/validations_test.rb b/activerecord/test/cases/validations_test.rb
index db8159eff8..959c58aa85 100644
--- a/activerecord/test/cases/validations_test.rb
+++ b/activerecord/test/cases/validations_test.rb
@@ -149,4 +149,17 @@ class ValidationsTest < ActiveRecord::TestCase
     assert_equal 1, Company.validators_on(:name).size
   end
 
+  def test_numericality_validation_with_mutation
+    Topic.class_eval do
+      attribute :wibble, ActiveRecord::Type::String.new
+      validates_numericality_of :wibble, only_integer: true
+    end
+
+    topic = Topic.new(wibble: '123-4567')
+    topic.wibble.gsub!('-', '')
+
+    assert topic.valid?
+  ensure
+    Topic.reset_column_information
+  end
 end