Remove --debug flag

[Kludex]

• Closes Phase out debug in favour of reload #480

I've created #1190 some time ago, but at the time I didn't remember why I was creating that PR.

The goal of this PR is to remove the --debug flag. This flag is actually hidden, so to be aware of its existence, you need to check uvicorns source code.

There's also a conditional on the DebugMiddleware, that makes the flag only useful if the exception happens before the http.response.start is sent from the application.

Consider the application:

async def app(scope, send, receive):
    raise Exception("HAHAH")

What the --debug flag returns for the client is:

❯ http GET :8000/         
HTTP/1.1 500 Internal Server Error
Transfer-Encoding: chunked
content-type: text/plain; charset=utf-8
date: Sun, 11 Sep 2022 12:15:46 GMT
server: uvicorn

Traceback (most recent call last):
  File "/home/marcelo/Development/encode/uvicorn/uvicorn/middleware/debug.py", line 104, in __call__
    await self.app(scope, receive, inner_send)
  File "/home/marcelo/Development/test/./main.py", line 2, in app
    raise Exception("HAHAH")
Exception: HAHAH

Without the flag, we have the same log on the server side, but the client receives the normal:

❯ http GET :8000/
HTTP/1.1 500 Internal Server Error
Transfer-Encoding: chunked
connection: close
content-type: text/plain; charset=utf-8
date: Sun, 11 Sep 2022 12:26:05 GMT
server: uvicorn

Internal Server Error

If we are using a web framework that handles exceptions, like Starlette, the --debug flag is completely useless, as the application already sets the Internal Server Error by default, see:

from starlette.applications import Starlette
from starlette.routing import Route


async def endpoint(request):
    raise Exception("haha")


app = Starlette(routes=[Route("/", endpoint)])

With the above application, and the --debug flag set, we have the following on the client side:

❯ http GET :8000/
HTTP/1.1 500 Internal Server Error
content-length: 21
content-type: text/plain; charset=utf-8
date: Sun, 11 Sep 2022 12:28:52 GMT
server: uvicorn

Internal Server Error

To summarize: this flag is not used, it doesn't bring much benefit, and we have a 3 years old issue to remove it.

[euri10]

agreed, just need to fix the coverage, not sure why removing all that code makes it drop..

[Kludex]

This is quite interesting actually... I have a different behavior on line 193 in the config.py file on two different python versions... I didn't expect that. There must be something there that I'm not aware... Which is not related to this PR.

I'll check later on.

[Kludex]

I've rerun the pipeline and the line that was marked as not covered on Python 3.7 is now covered, and another line became uncovered... What's happening here... 😅

[Kludex]

There's some random behavior on the reload_directory_structure for Python 3.7.

I'm dropping 0.04 coverage for this. It would be cool to increase this number to 100%. 😞

[Kludex]

agreed, just need to fix the coverage, not sure why removing all that code makes it drop..

Answering this... If you have 100 potatoes, and 10 are bad potatoes, 90% are good. If you eat 10 potatoes, you have 80 potatoes, 80/90 = 88.8% potatoes are good. Same idea when removing lines of code that are covered.

[edmorley]

@Kludex Hi! Should the middleware file itself be deleted too? It's currently both unused and untested:
https://github.com/encode/uvicorn/blob/master/uvicorn/middleware/debug.py

[Kludex]

That's why the coverage dropped...

Yes. I missed that. Would you like to create a PR @edmorley ? 👀