env: Add detection for environment using systemd-nspawn

Signed-off-by: Nathan Chancellor <[email protected]>

fish/functions/using_nspawn.fish

@@ -0,0 +1,7 @@
+#!/usr/bin/env fish
+# SPDX-License-Identifier: MIT
+# Copyright (C) 2022-2023 Nathan Chancellor
+
+function using_nspawn -d "Checks if host is using systemd-nspawn for development container"
+    PYTHONPATH=$PYTHON_FOLDER python3 -c 'import lib.utils, sys; sys.exit(0 if lib.utils.using_nspawn() else 1)'
+end

python/lib/utils.py

@@ -101,6 +101,12 @@ def in_container():
         '/.dockerenv').is_file()
 
 
+def in_nspawn():
+    # An nspawn container has to have systemd-detect-virt but this may not
+    # always run where systemd-detect-virt exists.
+    return shutil.which('systemd-detect-virt') and detect_virt('-c') == 'systemd-nspawn'
+
+
 def path_and_text(*args):
     if (path := Path(*args)).exists():
         return path, path.read_text(encoding='utf-8')
@@ -184,6 +190,11 @@ def run_check_rc_zero(*args, **kwargs):
     return chronic(*args, **kwargs, check=False).returncode == 0
 
 
+def using_nspawn():
+    etc_nspawn = Path('/etc/systemd/nspawn')
+    return etc_nspawn.exists() and list(etc_nspawn.iterdir())
+
+
 def print_or_run_cmd(cmd, dryrun, end='\n\n'):
     if dryrun:
         print_cmd(cmd, end=end)