Use String#+@ before mutating the result of Symbol#to_s

[eregon]

• String#+@ is available since Ruby 2.3.
• See the upstream Ruby change making Symbol#to_s return a frozen String
  for efficiency: Make Symbol#to_s return a frozen String, the same String for a given Symbol ruby/ruby#2437

Summary

Ruby 2.7 will return a frozen String for Symbol#to_s to avoid extra allocations:
ruby/ruby#2437
https://bugs.ruby-lang.org/issues/16150#note-18

That is currently an experimental change, but I think it would make a lot of sense and I would expect only few places need to be adapted to handle a frozen Symbol#to_s.

[eregon]

FWIW, I also tried to use only immutable Strings, but the change is then larger:

diff --git a/activesupport/lib/active_support/ordered_options.rb b/activesupport/lib/active_support/ordered_options.rb
index c4e419f546..6d61f9a38d 100644
--- a/activesupport/lib/active_support/ordered_options.rb
+++ b/activesupport/lib/active_support/ordered_options.rb
@@ -40,13 +40,11 @@ def [](key)
 
     def method_missing(name, *args)
       name_string = name.to_s
-      if name_string.chomp!("=")
-        self[name_string] = args.first
+      if name_string.end_with?('=')
+        self[name_string[0..-2]] = args.first
       else
-        bangs = name_string.chomp!("!")
-
-        if bangs
-          self[name_string].presence || raise(KeyError.new(":#{name_string} is blank"))
+        if name_string.end_with?("!")
+          self[name_string[0..-2]].presence || raise(KeyError.new("#{name.inspect} is blank"))
         else
           self[name_string]
         end

[kamipo]

Related ruby/ruby#2487.

[byroot]

I would expect only few places need to be adapted to handle a frozen Symbol#to_s.

That's the only change I had to do when I tested ruby/ruby#2175 against Redmine.

There's definitely some stuff that will break out there, but it's both relatively rare and extremely easy fixes.

[casperisfine]

👍 to this.

cc @rafaelfranca

[eregon]

Thanks for the quick merge!

[byroot]

Can we also backport it?

Assuming this experiment isn't reverted (🤞) MRI 2.7 will be released in about 3 months, so It would be better if people didn't hit that issue with the supported versions of Rails.

[kamipo]

Yeah, I will do that later today (l’m out of home now).

[eregon]

Could we backport this change to both Rails 6.0 and 5.2 so people can use Ruby 2.7 on those Rails versions? For 5.2 we can use name.to_s.dup or #37303 (comment)

[rafaelfranca]

Backported.

[eregon]

Thank you!
I added a comment on the 5.2 backport, I am not sure we can use String#+@ there for Ruby 2.2: ed81031#commitcomment-35254852