TOX_OVERRIDE=testenv.pass_env=+FOO drops config values from testenv.passenv in tox.ini

[vlotorev]

Issue

Create tox.ini with contents:

$ cat tox.ini
[testenv]
passenv = FOO

This output matches expected - FOO var is present in pass_env:

$ tox config -k pass_env | grep --extended-regexp 'FOO|BAR'
  FOO

This output matches expected - both FOO and BAR in pass_env:

$ TOX_OVERRIDE=testenv.passenv+=BAR tox config -k pass_env | grep --extended-regexp 'FOO|BAR'
  BAR
  FOO

This output doesn't match expected - only BAR is present, but FOO from tox.ini is missing (note that TOX_OVERRIDE is using pass_env, tox.ini declares passenv):

$ TOX_OVERRIDE=testenv.pass_env+=BAR tox config -k pass_env | grep --extended-regexp 'FOO|BAR'
  BAR

Environment

• OS: CentOS Stream 9

$ pip list
Package       Version
------------- -------
cachetools    5.5.0
chardet       5.2.0
colorama      0.4.6
distlib       0.3.8
filelock      3.16.1
packaging     24.1
pip           23.2.1
platformdirs  4.3.6
pluggy        1.5.0
pyproject-api 1.8.0
tox           4.20.0
virtualenv    20.26.5

Output of running tox

Output of tox -rvv

$ tox -rvv
py: 90 W remove tox env folder /home/vlotorev/tmp/tox/.tox/py [tox/tox_env/api.py:324]
py: 94 I find interpreter for spec PythonSpec(path=/home/vlotorev/tmp/tox/venv/bin/python3.12) [virtualenv/discovery/builtin.py:72]
py: 94 D filesystem is case-sensitive [virtualenv/info.py:25]
py: 95 D got python info of %s from (PosixPath('/usr/bin/python3.12'), PosixPath('/home/vlotorev/.local/share/virtualenv/py_info/1/f0d7a494a3f776233427cb85a7e198c7cf4913b50a203c6febc678cc4f5bf265.json')) [virtualenv/app_data/via_disk_folder.py:131]
py: 95 I proposed PythonInfo(spec=CPython3.12.1.final.0-64, system=/usr/bin/python3.12, exe=/home/vlotorev/tmp/tox/venv/bin/python3.12, platform=linux, version='3.12.1 (main, Feb 19 2024, 00:00:00) [GCC 11.4.1 20231218 (Red Hat 11.4.1-3)]', encoding_fs_io=utf-8-utf-8) [virtualenv/discovery/builtin.py:79]
py: 95 D accepted PythonInfo(spec=CPython3.12.1.final.0-64, system=/usr/bin/python3.12, exe=/home/vlotorev/tmp/tox/venv/bin/python3.12, platform=linux, version='3.12.1 (main, Feb 19 2024, 00:00:00) [GCC 11.4.1 20231218 (Red Hat 11.4.1-3)]', encoding_fs_io=utf-8-utf-8) [virtualenv/discovery/builtin.py:81]
py: 108 I create virtual environment via CPython3Posix(dest=/home/vlotorev/tmp/tox/.tox/py, clear=False, no_vcs_ignore=False, global=False) [virtualenv/run/session.py:50]
py: 109 D create folder /home/vlotorev/tmp/tox/.tox/py/bin [virtualenv/util/path/_sync.py:12]
py: 109 D create folder /home/vlotorev/tmp/tox/.tox/py/lib/python3.12/site-packages [virtualenv/util/path/_sync.py:12]
py: 109 D create folder /home/vlotorev/tmp/tox/.tox/py/lib64/python3.12/site-packages [virtualenv/util/path/_sync.py:12]
py: 109 D write /home/vlotorev/tmp/tox/.tox/py/pyvenv.cfg [virtualenv/create/pyenv_cfg.py:33]
py: 109 D       home = /usr/bin [virtualenv/create/pyenv_cfg.py:38]
py: 109 D       implementation = CPython [virtualenv/create/pyenv_cfg.py:38]
py: 109 D       version_info = 3.12.1.final.0 [virtualenv/create/pyenv_cfg.py:38]
py: 109 D       virtualenv = 20.26.5 [virtualenv/create/pyenv_cfg.py:38]
py: 109 D       include-system-site-packages = false [virtualenv/create/pyenv_cfg.py:38]
py: 109 D       base-prefix = /usr [virtualenv/create/pyenv_cfg.py:38]
py: 109 D       base-exec-prefix = /usr [virtualenv/create/pyenv_cfg.py:38]
py: 109 D       base-executable = /usr/bin/python3.12 [virtualenv/create/pyenv_cfg.py:38]
py: 109 D symlink /usr/bin/python3.12 to /home/vlotorev/tmp/tox/.tox/py/bin/python [virtualenv/util/path/_sync.py:32]
py: 109 D create virtualenv import hook file /home/vlotorev/tmp/tox/.tox/py/lib/python3.12/site-packages/_virtualenv.pth [virtualenv/create/via_global_ref/api.py:91]
py: 110 D create /home/vlotorev/tmp/tox/.tox/py/lib/python3.12/site-packages/_virtualenv.py [virtualenv/create/via_global_ref/api.py:94]
py: 110 D ============================== target debug ============================== [virtualenv/run/session.py:52]
py: 110 D debug via /home/vlotorev/tmp/tox/.tox/py/bin/python /home/vlotorev/tmp/tox/venv/lib64/python3.12/site-packages/virtualenv/create/debug.py [virtualenv/create/creator.py:200]
py: 110 D {
  "sys": {
    "executable": "/home/vlotorev/tmp/tox/.tox/py/bin/python",
    "_base_executable": "/usr/bin/python3.12",
    "prefix": "/home/vlotorev/tmp/tox/.tox/py",
    "base_prefix": "/usr",
    "real_prefix": null,
    "exec_prefix": "/home/vlotorev/tmp/tox/.tox/py",
    "base_exec_prefix": "/usr",
    "path": [
      "/usr/lib64/python312.zip",
      "/usr/lib64/python3.12",
      "/usr/lib64/python3.12/lib-dynload",
      "/home/vlotorev/tmp/tox/.tox/py/lib64/python3.12/site-packages",
      "/home/vlotorev/tmp/tox/.tox/py/lib/python3.12/site-packages"
    ],
    "meta_path": [
      "<class '_virtualenv._Finder'>",
      "<class '_frozen_importlib.BuiltinImporter'>",
      "<class '_frozen_importlib.FrozenImporter'>",
      "<class '_frozen_importlib_external.PathFinder'>"
    ],
    "fs_encoding": "utf-8",
    "io_encoding": "utf-8"
  },
  "version": "3.12.1 (main, Feb 19 2024, 00:00:00) [GCC 11.4.1 20231218 (Red Hat 11.4.1-3)]",
  "makefile_filename": "/usr/lib64/python3.12/config-3.12-x86_64-linux-gnu/Makefile",
  "os": "<module 'os' (frozen)>",
  "site": "<module 'site' (frozen)>",
  "datetime": "<module 'datetime' from '/usr/lib64/python3.12/datetime.py'>",
  "math": "<module 'math' from '/usr/lib64/python3.12/lib-dynload/math.cpython-312-x86_64-linux-gnu.so'>",
  "json": "<module 'json' from '/usr/lib64/python3.12/json/__init__.py'>"
} [virtualenv/run/session.py:53]
py: 125 I add seed packages via FromAppData(download=False, pip=bundle, via=copy, app_data_dir=/home/vlotorev/.local/share/virtualenv) [virtualenv/run/session.py:57]
py: 125 D got embed update of distribution %s from ('pip', PosixPath('/home/vlotorev/.local/share/virtualenv/wheel/3.12/embed/3/pip.json')) [virtualenv/app_data/via_disk_folder.py:131]
py: 126 D install pip from wheel /home/vlotorev/tmp/tox/venv/lib64/python3.12/site-packages/virtualenv/seed/wheels/embed/pip-24.2-py3-none-any.whl via CopyPipInstall [virtualenv/seed/embed/via_app_data/via_app_data.py:49]
py: 127 D copy directory /home/vlotorev/.local/share/virtualenv/wheel/3.12/image/1/CopyPipInstall/pip-24.2-py3-none-any/pip-24.2.dist-info to /home/vlotorev/tmp/tox/.tox/py/lib/python3.12/site-packages/pip-24.2.dist-info [virtualenv/util/path/_sync.py:40]
py: 128 D copy /home/vlotorev/.local/share/virtualenv/wheel/3.12/image/1/CopyPipInstall/pip-24.2-py3-none-any/pip-24.2.virtualenv to /home/vlotorev/tmp/tox/.tox/py/lib/python3.12/site-packages/pip-24.2.virtualenv [virtualenv/util/path/_sync.py:40]
py: 129 D copy directory /home/vlotorev/.local/share/virtualenv/wheel/3.12/image/1/CopyPipInstall/pip-24.2-py3-none-any/pip to /home/vlotorev/tmp/tox/.tox/py/lib/python3.12/site-packages/pip [virtualenv/util/path/_sync.py:40]
py: 236 D generated console scripts pip3.12 pip pip-3.12 pip3 [virtualenv/seed/embed/via_app_data/pip_install/base.py:43]
py: 236 I add activators for Bash, CShell, Fish, Nushell, PowerShell, Python [virtualenv/run/session.py:63]
py: 238 D write /home/vlotorev/tmp/tox/.tox/py/pyvenv.cfg [virtualenv/create/pyenv_cfg.py:33]
py: 238 D       home = /usr/bin [virtualenv/create/pyenv_cfg.py:38]
py: 239 D       implementation = CPython [virtualenv/create/pyenv_cfg.py:38]
py: 239 D       version_info = 3.12.1.final.0 [virtualenv/create/pyenv_cfg.py:38]
py: 239 D       virtualenv = 20.26.5 [virtualenv/create/pyenv_cfg.py:38]
py: 239 D       include-system-site-packages = false [virtualenv/create/pyenv_cfg.py:38]
py: 239 D       base-prefix = /usr [virtualenv/create/pyenv_cfg.py:38]
py: 239 D       base-exec-prefix = /usr [virtualenv/create/pyenv_cfg.py:38]
py: 239 D       base-executable = /usr/bin/python3.12 [virtualenv/create/pyenv_cfg.py:38]