Support freezing string literals in templates

[mitchellhenke]

Feature request

While I was working with config.action_view.frozen_string_literal in Rails (rails/rails#43725), I noticed that in some of our views we were still allocating identical strings repeatedly. I was kind of curious why, and noticed that it was due to our usage of view_component and string literals in view_component templates were not being frozen. As mentioned in the linked PR, the string literals can be significant parts of templates.

It would be neat to have the performance gain available here too!

Motivation

This would strictly be a performance improvement as I understand it.

[camertron]

Hey @mitchellhenke, fantastic idea, thank you! We would welcome a PR that introduces this capability. I would look specifically to inject the # frozen_string_literal: true comment anywhere we're using class_eval in the compiler, for example here.

I verified that the magic comment works with class_eval as well as eval:

class Foo
  class_eval(<<~END)
    # frozen_string_literal: true
    def foo
      "foo"
    end
  END
end

irb> Foo.new.foo.frozen?
=> true

[camertron]

Oh lol I totally missed the PR you submitted for this, carry on!