Implement `HashWithIndifferentAccess#to_proc`

Previously, calling `#to_proc` on `HashWithIndifferentAccess` object used inherited `#to_proc`
method from the `Hash` class, which was not able to access values using indifferent keys.

Fixes #48770.

activesupport/CHANGELOG.md

@@ -1,2 +1,8 @@
+*   Implement `HashWithIndifferentAccess#to_proc`.
+
+    Previously, calling `#to_proc` on `HashWithIndifferentAccess` object used inherited `#to_proc`
+    method from the `Hash` class, which was not able to access values using indifferent keys.
+
+    *fatkodima*
 
 Please check [7-1-stable](https://github.com/rails/rails/blob/7-1-stable/activesupport/CHANGELOG.md) for previous changes.

activesupport/lib/active_support/hash_with_indifferent_access.rb

@@ -387,6 +387,10 @@ module ActiveSupport
       _new_hash
     end
 
+    def to_proc
+      proc { |key| self[key] }
+    end
+
     private
       if Symbol.method_defined?(:name)
         def convert_key(key)

activesupport/test/hash_with_indifferent_access_test.rb

@@ -965,4 +965,13 @@ class HashWithIndifferentAccessTest < ActiveSupport::TestCase
     assert_equal :bar, hash_wia[:foo]
     assert_equal :baz, hash_wia[:missing]
   end
+
+  def test_indifferent_to_proc
+    @strings = @strings.with_indifferent_access
+    proc = @strings.to_proc
+
+    assert_equal 1, proc["a"]
+    assert_equal 1, proc[:a]
+    assert_nil proc[:no_such]
+  end
 end