Address warning: literal string will be frozen in the future warnings

[yahonda]

This commit addresses the warning: literal string will be frozen in the future warnings appeared at Rails CI https://buildkite.com/rails/rails-nightly/builds/1122#019263a3-2200-4e62-a6a8-028cffa60aaf

Here are the warnings appeared:

/usr/local/lib/ruby/gems/3.4.0+0/bundler/gems/httpclient-d57cc6d5ffee/lib/httpclient.rb:1256: warning: literal string will be frozen in the future
/usr/local/lib/ruby/gems/3.4.0+0/bundler/gems/httpclient-d57cc6d5ffee/lib/httpclient/http.rb:580: warning: literal string will be frozen in the future
/usr/local/lib/ruby/gems/3.4.0+0/bundler/gems/httpclient-d57cc6d5ffee/lib/httpclient/session.rb:954: warning: literal string will be frozen in the future
/usr/local/lib/ruby/gems/3.4.0+0/bundler/gems/httpclient-d57cc6d5ffee/lib/httpclient/util.rb:71: warning: literal string will be frozen in the future

There should be some warnings remained because Rails CI does not use all of httpclient code. I'll open some pull requests later to address remaining ones.

Ref: https://bugs.ruby-lang.org/issues/20205

[hartator]

I think we should reasonably push back on these new warnings and the restriction itself.

I don't think they realized how big of an impact it will be while negatively impacting performance at least in the short term.

I have added a note: https://bugs.ruby-lang.org/issues/20205#note-55

[hsbt]

I also found warnings by stdlib with @yahonda:

/Users/hsbt/.local/share/rbenv/versions/ruby-dev/lib/ruby/3.4.0+0/open-uri.rb:455: warning: literal string will be frozen in the future
/Users/hsbt/.local/share/rbenv/versions/ruby-dev/lib/ruby/3.4.0+0/logger/log_device.rb:45: warning: literal string will be frozen in the future

@mame found open-uri warning caused by

def set_body_encoding
  if type = self.content_type
    OpenURI::Meta.init(o = '')
    o.meta_add_field('content-type', type)
    @body_encoding = o.encoding
  end
end

from https://github.com/nahi/httpclient/blob/master/lib/httpclient/http.rb#L241

It's hard to fix that from open-uri warnings.

[byroot]

The warning isn't really from open-uri but from passing a literal to a method that mutate the argument.

The fix is to do: OpenURI::Meta.init(o = ''.dup)

[byroot]

Suggested change

	content = block ? nil : String.new('')
	content = block ? nil : ''.dup

Why not a simple .dup?

[yahonda]

Since these strings starts out as an empty string and the string is added later with the << method, I was feeling like it seemed more appropriate to create empty string via String.new than duplicating an empty string. However, I do not have strong opinion on this so let me update them to use dup.

[byroot]

An easy way to solve these warnings is to run ruby with --enable-frozen-string-literal --debug-frozen-string-literal, this will include the location where the string was allocated in the FrozenError message.

[jeremy]

Looks like HTTP::Message::Body#dump and #dump_chunked need to be fixed as well. Both have frozen empty strings as default args.

[jeremy]

Covered other cases in #465