From: "byroot (Jean Boussier) via ruby-core" <ruby-core@...>
Date: 2025-04-16T23:24:08+00:00
Subject: [ruby-core:121678] [Ruby Feature#21269] Opt in to raise for modification of chilled strings returned from `Symbol#to_s`

Issue #21269 has been updated by byroot (Jean Boussier).


I understand the ask, and that's something we considered with @etienne when we implemented it, but I thought it was too weird for `--enable=frozen-string-literal` to impact something that isn't a literal.

A pattern I use a lot for this sort of things is to turn warnings into errors globally by decorating `Warning.warn`, for instance: https://github.com/rails/rails/blob/66732971111a62e5940268e1daf7d413c72a234f/tools/strict_warnings.rb

Some test frameworks like minitest have this feature built-in now: https://github.com/minitest/minitest/blob/4dcad89a788e56f8abb30952ed839a41f1b3ec6e/lib/minitest/error_on_warning.rb

----------------------------------------
Feature #21269: Opt in to raise for modification of chilled strings returned from `Symbol#to_s`
https://bugs.ruby-lang.org/issues/21269#change-112729

* Author: Earlopain (Earlopain _)
* Status: Open
----------------------------------------
Ref https://bugs.ruby-lang.org/issues/20350

```rb
begin
  :foo.to_s << "bar"
  puts "ok sym"
rescue
  puts "fail sym"
end

begin
  "foo" << "bar"
  puts "ok str"
rescue
  puts "failed str"
end
```

Output with `RUBYOPT="--enable=frozen-string-literal -W"`:
```
test.rb:2: warning: string returned by :foo.to_s will be frozen in the future
ok sym
failed str
```

`--enable=frozen-string-literal` does something for string literals, I would like the same for `Symbol#to_s`. I would suggest simply reusing `--enable=frozen-string-literal` but its name seems very clear about being about string literals, which doesn't really fit for what's going on with symbols here.

For convenience, it would be very nice to have just a single switch for this though.



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