Should `uri_for` avoid prepending the base URI to absolute URIs?

[fgabolde]

Currently if you do something weird like

$request->uri_for('http://example.com')

it just tries to rebase the argument anyway:

http://localhost:5000/mountpoint/http://example.com

I'd argue that this is never what the user wants, so the method should either throw an exception or not rebase the argument (returning "http://example.com" unchanged).

For selfish reasons I prefer the second option. Possibly both options should be provided by different methods.