Use WSGI `SCRIPT_NAME` as path prefix if defined

[kmohrf]

Describe the bug

The application server (like Gunicorn) or reverse proxy may set SCRIPT_NAME, which is an WSGI environment variable that can be used to serve an application under a path prefix. This has a similar purpose and is related to, but should not be confused with Django’s own FORCE_SCRIPT_NAME setting.

When generating URLs the content of SCRIPT_NAME should be used as a prefix for the generated pathname. Django does this by default now. However, paths in schema generated by drf-spectacular’s do not have this prefix. Instead they are generated as if SCRIPT_NAME were an empty string.

To Reproduce

I’ve created a small repo with minimal configuration to demonstrate the issue:
https://github.com/kmohrf/django_script_name_test

The schema UI under /my-prefix/api/schema/ui/ is actually a nice demonstration because the schema URL directly below the header has the prefix whereas all the paths in the documentation below it don’t have it.

Expected behavior

If SCRIPT_NAME is a non-empty string, all paths in the schema should be prefixed with the content of SCRIPT_NAME.

Thank you for all your work on drf-spectacular and for your time investigating this issue.
Please let me know if I can provide any additional information!

Cheers

Konrad