Forward HOME by default

[gschaffner]

this ensures that os.path.expanduser and pathlib.Path.expanduser work by default inside a tox environment on non-Windows systems, including those without /etc/passwd.

fixes #2702.

this patch is analogous to #519.

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• ran the linter to address style issues (tox -e fix)
• wrote descriptive pull request text
• ensured there are test(s) validating the fix
  • i haven't done this because it is nontrivial to add tests that run on a system without /etc/passwd. the easiest way to get such a system is an OCI container, e.g.

    #!/usr/bin/env -S sh -c '< "$0" podman run --rm -i -v "$(dirname "$(realpath "$0")")":/tox-ro:ro nixery.dev/bash/coreutils/python311/git bash "$@"'
    
    set -o errexit -o errtrace -o nounset -o pipefail
    shopt -s inherit_errexit
    
    cd "$(mktemp -d)"
    python -m venv .venv &> /dev/null
    . .venv/bin/activate
    cp -r /tox-ro /tox
    
    set -o xtrace
    
    pip install -q /tox
    mkdir proj
    cd proj
    mkdir -p src/hello
    touch pyproject.toml src/hello/__init__.py
    printenv HOME
    cat /etc/passwd || true
    tox --colored yes

    but it's perhaps not worth the overhead to do that for this somewhat esoteric test.
• added news fragment in docs/changelog folder
• updated/extended the documentation
  • i haven't done this because the default pass_env on various platforms is not documented:

    tox/docs/config.rst

    Lines 279 to 281 in 079f839

    	.. conf::
    	:keys: pass_env, passenv
    	:default: <empty list>

[gschaffner]

the pre-commit isort failure is unrelated to these changes; see #2908.

[gaborbernat]

I'd rather pass this on all platforms.

[gschaffner]

if https://superuser.com/a/607110 and https://stackoverflow.com/a/36392591 are correct, HOME isn't relevant on windows and USERPROFILE is the windows equivalent of it. USERPROFILE is already forwarded on windows:

tox/src/tox/tox_env/api.py

Lines 224 to 233 in 4408cff

	if sys.platform == "win32": # pragma: win32 cover
	env.extend(
	[
	"TEMP", # temporary file location
	"TMP", # temporary file location
	"USERPROFILE", # needed for `os.path.expanduser()`
	"PATHEXT", # needed for discovering executables
	"MSYSTEM", # controls paths printed format
	],
	)

[gaborbernat]

True, but for consistency what's the harm passing the HOME universally?

[gschaffner]

none that i know of :)

do you want me to update this patch so it changes TMPDIR to be forwarded on windows too?

[gaborbernat]

Not that one.