I'm not sure I completely understand but I can imagine it doesn't make sense to use any gui backend if the user is not logged in and hence has no display.

The quick fix is for nix to set the MPLBACKEND=agg env for those packages when running tests.

For linux we have a helper to detect if we have a usable display and if not, the auto-backend selection falls back to a non-interactive backend. I suspect that something similar is possible for OSX to detect if we have a usable GUI display.

I tried to reproduce this by sshing into a mac without being logged in, but that failed in other ways (blocking show() blocked...forever and there was no window even after I logged in).

I think this is a good first issue because it will be adding a private helper function + one or two calls to it in the backend selection logic and/or the backend start up code.

Tasks:

• sort out if there is a way (could be in objective-c) to detect if we can actually make a window
• skip GUI backends on OSX if we do not have a functioning display
• work out a way to test this (we do have OSX CI jobs and standard ways of running tests in sub-processes) or make a good case as to why we can not test this under CI / developer machines (e.g. we need elevated privileges / to make a new user / log the user out to drive the system to a broken state)

I would say this is medium difficulty as it is possible that there is a call in the OSX SDK that just answers this question, but might require research to find it. You will also have to understand the auto backend selection logic.

Good first issue - notes for new contributors

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I labeled this as 3.9 to keep it out of our 3.8 wrap up workstream for now. If this ends up being simple no problem in backporting it to 3.8.x .

Thank you for responding! I cobbled together these reproduction steps on my macOS 13.4.1 M1 machine:

1. Suppose we are currently logged in with username me.
2. Set up test directory:

cd ~
mkdir matplotlib-test
cd matplotlib-test
python -m venv env
source env/bin/activate
pip install matplotlib

3. Create a script test.py:

import matplotlib.pyplot as plt

figure = plt.figure()

4. Verify that python test.py does not crash.
5. Create a new user named someuser:

sudo dscl . -create /Users/someuser
sudo dscl . -create /Users/someuser UserShell /bin/bash
sudo dscl . -create /Users/someuser RealName "Some User"
sudo dscl . -create /Users/someuser UniqueID "1010"
sudo dscl . -create /Users/someuser PrimaryGroupID 80
sudo dscl . -create /Users/someuser NFSHomeDirectory /Users/someuser
sudo dscl . -passwd /Users/someuser password
sudo mkdir /Users/someuser

6. Temporarily give access to me's home directory:

sudo chmod 777 /Users/me

7. Become someuser (password is password):

su - someuser
cd /Users/me/matplotlib-test
source env/bin/activate

8. Verify that python test.py crashes:

(env) -bash-3.2$ python test.py
Matplotlib created a temporary cache directory at /tmp/matplotlib-m4igy099 because the default path (/Users/someuser/.matplotlib) is not a writable directory; it is highly recommended to set the MPLCONFIGDIR environment variable to a writable directory, in particular to speed up the import of Matplotlib and to better support multiprocessing.
2023-07-12 09:53:30.523 Python[87901:57870394] XType: Using static font registry.
Trace/BPT trap: 5

9. Restore everything:

sudo chmod 750 /Users/me
sudo dscl . -delete /Users/someuser
sudo rm -rf /Users/someuser

Thank you for the reproduction examples but that is not something we can put in the test suite!

I wonder if we look at the list of screens, it would be empty in this case?