Handle frozen conditions in validate

Co-authored-by: Rafael França <rafael@franca.dev>

activemodel/lib/active_model/validations.rb

@@ -163,10 +163,10 @@ module ActiveModel
         if options.key?(:on)
           options = options.dup
           options[:on] = Array(options[:on])
-          options[:if] = Array(options[:if])
-          options[:if].unshift ->(o) {
-            !(options[:on] & Array(o.validation_context)).empty?
-          }
+          options[:if] = [
+            ->(o) { !(options[:on] & Array(o.validation_context)).empty? },
+            *options[:if]
+          ]
         end
 
         set_callback(:validate, *args, options, &block)

activemodel/test/cases/validations_test.rb

@@ -159,6 +159,12 @@ class ValidationsTest < ActiveModel::TestCase
     assert_equal ["will never be valid"], t.errors["title"]
   end
 
+  def test_validates_with_array_condition_does_not_mutate_the_array
+    opts = []
+    Topic.validate(if: opts, on: :create) { }
+    assert_empty opts
+  end
+
   def test_invalid_validator
     Topic.validate :i_dont_exist
     assert_raises(NoMethodError) do