use env config path for system config path when no system config path

[minrk]

SYSTEM_CONFIG_PATH hasn't technically been guaranteed to be non-empty, but jupyter-server has assumed it is: jupyter-server/jupyter_server#1527 and in practice, it ~always has been until 5.8 because the empty case was weird and rare.

We already use sys.prefix for SYSTEM_JUPYTER_PATH in a similar situation, so it's probably simplest to do the same in config path.

cc @krassowski

I can do a 5.8.1 with this.

[krassowski]

I'm not sure if this will not have any unintended side-effects, but it sounds like it's a better situation than having jupyter server extension not work at all.

We already use sys.prefix for SYSTEM_JUPYTER_PATH in a similar situation, so it's probably simplest to do the same in config path.

I could not find that maybe I am just too tired), can you leave a reference for posterity?

[minrk]

Sure, the same condition is here for Jupyter path:

jupyter_core/jupyter_core/paths.py

Line 243 in cca263a

SYSTEM_JUPYTER_PATH = [str(Path(sys.prefix, "share", "jupyter"))]

[minrk]

I looked around, and jupyter-server/jupyter_server#1527 is the only reference to SYSTEM_CONFIG_PATH I can find that would be sensitive to this. All readers of this path rely on jupyter_config_path which handles this and avoids duplicate entries (with a test verifying it), so I think this should be safe.