@myronmarston how would you feel about adding: 

* `RSpec::Support.warning_message` which generates the full warning message string
* `RSpec::Support.show_warning` that just takes a string and shows it.

`RSpec.warn_with` from support can then just call these two methods.

`RSpec.warn_with` from core would then do the following things:

1. call `RSpec::Support.warning_message`
2. add its parts to the warning message
3. call `RSpec::Support.show_warning`