Anything that depends on `RSpec.configuration` can't go in rspec-support (unless it is tolerant of it not being loaded) because `RSpec.configuration` is exposed by rspec-core and the other gems need to be usable on their own without rspec-core.

What I would do is something like:

``` ruby
module RSpec
  if respond_to?(:configuration)
    def self.deprecate(deprecated, data = {})
      # version that depends on RSpec.configuration
    end
  else
    def self.deprecate(deprecated, data = {})
      # version that does not depend on RSpec.configuration
    end
  end
end
```

(Really, the conditional should probably wrap multiple method defs here since multiple use `RSpec.configuration`.)