print warning when server_name and cur_server_name don't match

[Alexis-benoist]

If the server name is misconfigured, the subdomain is '<invalid>' and no warning is printed.

werkzeug/werkzeug/routing.py

Line 1302 in d637320

if cur_server_name[offset:] != real_server_name:

An improvement could be to print a warning if the names don't match, instead of just returning 404 errors for all pages.

[npdoty]

I just spent multiple days trying to debug a Flask application that returned 404s for every request with no indication as to why the routes weren't being matched. It would help troubleshooting enormously if there were a visible warning when this mismatch occurs.

[WCICS]

I had the same issue. This should probably be an error, but there must atleast be a warning, as otherwise we have to dig through werkzeug source code just to find out that we have a config issue.