Literal string will be frozen deprecation warning in Ruby 3.4

[NGMarmaduke]

Using Ruby version 3.4.1 and add Warning[:deprecated] = true to spec_helper.rb results in numerous deprecation warnings due to the mutation of literal strings.

One example:

/Users/nick/projects/phony/lib/phony/country_codes.rb:158: warning: literal string will be frozen in the future (run with --debug-frozen-string-literal for more information)

Looking at the majority of warnings they are due to the use of String#slice!.

I started to work on a patch to fix the warnings however in some cases it seems as though the gem is relying on the mutation of arguments. I've attached a patch for one example in the 'trunk_code.rb'. Updating split to not mutate national_number causes qed test failures.

From 5ddb8251fcf7b910850a3c7ce3fd9641f280e2b0 Mon Sep 17 00:00:00 2001
From: Nick Maher <[email protected]>
Date: Mon, 30 Dec 2024 10:07:08 +0000
Subject: [PATCH] Trunk code example

---
 lib/phony/trunk_code.rb | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/phony/trunk_code.rb b/lib/phony/trunk_code.rb
index c1dfae7..cd14eb7 100644
--- a/lib/phony/trunk_code.rb
+++ b/lib/phony/trunk_code.rb
@@ -29,8 +29,10 @@ module Phony
     # its parts.
     #
     def split(national_number)
-      national_number.gsub! @trunk_code_replacement, EMPTY_STRING if @split
-      [self, national_number]
+      return [self, national_number] unless @split
+
+      without_trunk = national_number.gsub @trunk_code_replacement, EMPTY_STRING
+      [self, without_trunk]
     end
 
     # Normalize normalizes the given national number.
-- 
2.42.1