task: metadata: install: pip install -e .[testing,docs]
patch: diff --git a/docs/changelog/2822.bugfix.rst b/docs/changelog/2822.bugfix.rst
new file mode 100644
index 00000000..3c0dc9d8
--- /dev/null
+++ b/docs/changelog/2822.bugfix.rst
@@ -0,0 +1,1 @@
+Require space after colon before factor filter expansion, unless it is the last character of the line - by :user:`pdecat`.
diff --git a/src/tox/config/loader/ini/factor.py b/src/tox/config/loader/ini/factor.py
index e13b5ec9..c429efb1 100644
--- a/src/tox/config/loader/ini/factor.py
+++ b/src/tox/config/loader/ini/factor.py
@@ -50,7 +50,7 @@ def expand_factors(value: str) -> Iterator[tuple[list[list[tuple[str, bool]]] |
     for line in value.split("\n"):
         factors: list[list[tuple[str, bool]]] | None = None
         marker_at, content = line.find(":"), line
-        if marker_at != -1:
+        if marker_at != -1 and (len(line) == marker_at + 1 or line[marker_at + 1] == " "):
             try:
                 factors = list(find_factor_groups(line[:marker_at].strip()))
             except ValueError:

problem_statement: tox-docker configuration parsing broken since tox 4.0.13
## Issue

tox-docker plugin configuration parsing of `ports`  is broken since tox 4.0.13.

`ports` configuration option is documented as:

> A multi-line list of port mapping specifications, as `HOST_PORT:CONTAINER_PORT/PROTO`, ...

With 4.0.12, the host port is properly set on the started container and forwarded to the container port.

But with tox 4.0.13, host port of the started container is random.
Given the short changelog for that release, I suspect it to be caused by https://github.com/tox-dev/tox/pull/2744
Same issue occurs with 4.0.15, 4.0.19, and 4.2.2.

## Environment

Provide at least:

- OS: Ubuntu 22.10
- `pip list` of the host Python where `tox` is installed:

```console
# poetry run pip list
Package            Version     Editable project location
------------------ ----------- -------------------------------------------------------------------------------------
attrs              21.4.0
black              22.3.0
boto3              1.23.6
botocore           1.26.6
cachetools         5.2.0
certifi            2022.5.18.1
cfgv               3.3.1
chardet            5.1.0
charset-normalizer 2.0.12
click              8.1.3
colorama           0.4.6
distlib            0.3.6
docker             5.0.3
filelock           3.9.0
flake8             4.0.1
freezegun          1.2.1
identify           2.5.1
idna               3.3
iniconfig          1.1.1
jmespath           1.0.0
mccabe             0.6.1
mock               4.0.3
mypy-extensions    0.4.3
nodeenv            1.6.0
packaging          22.0
pathspec           0.9.0
pip                22.3.1
platformdirs       2.6.2
pluggy             1.0.0
pre-commit         2.19.0
py                 1.11.0
pycodestyle        2.8.0
pyflakes           2.4.0
pyparsing          3.0.9
pyproject_api      1.4.0
pytest             6.2.5
pytest-mock        3.7.0
python-dateutil    2.8.2
PyYAML             6.0
requests           2.27.1
s3transfer         0.5.2
setuptools         65.6.3
six                1.16.0
toml               0.10.2
tomli              2.0.1
tox                4.2.2
tox-docker         4.0.0a2
urllib3            1.26.9
virtualenv         20.17.1
websocket-client   1.3.2
wheel              0.38.4
```

## Output of running tox

Provide the output of `tox -rvv`:

```console
tox -rvv
/home/patrick/workspaces/myproject/.venv/lib/python3.10/site-packages/requests/__init__.py:102: RequestsDependencyWarning: urllib3 (1.26.9) or chardet (5.1.0)/charset_normalizer (2.0.12) doesn't match a supported version!
  warnings.warn("urllib3 ({}) or chardet ({})/charset_normalizer ({}) doesn't match a supported "
py39: 298 W remove tox env folder /home/patrick/workspaces/myproject/.tox/py39 [tox/tox_env/api.py:321]
py39: 308 I find interpreter for spec PythonSpec(major=3, minor=9) [virtualenv/discovery/builtin.py:56]
py39: 308 D discover exe for PythonInfo(spec=CPython3.10.6.final.0-64, exe=/home/patrick/workspaces/myproject/.venv/bin/python, platform=linux, version='3.10.6 (main, Nov 14 2022, 16:10:14) [GCC 11.3.0]', encoding_fs_io=utf-8-utf-8) in /usr [virtualenv/discovery/py_info.py:437]
py39: 308 D filesystem is case-sensitive [virtualenv/info.py:24]
py39: 310 D got python info of /usr/bin/python3.10 from /home/patrick/.local/share/virtualenv/py_info/1/8a94588eda9d64d9e9a351ab8144e55b1fabf5113b54e67dd26a8c27df0381b3.json [virtualenv/app_data/via_disk_folder.py:129]
py39: 310 I proposed PythonInfo(spec=CPython3.10.6.final.0-64, system=/usr/bin/python3.10, exe=/home/patrick/workspaces/myproject/.venv/bin/python, platform=linux, version='3.10.6 (main, Nov 14 2022, 16:10:14) [GCC 11.3.0]', encoding_fs_io=utf-8-utf-8) [virtualenv/discovery/builtin.py:63]
py39: 310 D discover PATH[0]=/home/patrick/workspaces/myproject/.venv/bin [virtualenv/discovery/builtin.py:108]
py39: 311 D got python info of /home/patrick/workspaces/myproject/.venv/bin/python3 from /home/patrick/.local/share/virtualenv/py_info/1/f40e8b45bd8922e09aa5a9356903620c1975d00691ae8ec9747c29426f7f443d.json [virtualenv/app_data/via_disk_folder.py:129]
py39: 311 D discover exe from cache /usr - exact False: PythonInfo({'architecture': 64, 'base_exec_prefix': '/usr', 'base_prefix': '/usr', 'distutils_install': {}, 'exec_prefix': '/usr', 'executable': '/home/patrick/workspaces/myproject/.venv/bin/python', 'file_system_encoding': 'utf-8', 'has_venv': True, 'implementation': 'CPython', 'max_size': 9223372036854775807, 'original_executable': '/usr/bin/python3.10', 'os': 'posix', 'path': ['/home/patrick/.local/pipx/venvs/tox/lib/python3.10/site-packages/virtualenv/discovery', '/usr/lib/python310.zip', '/usr/lib/python3.10', '/usr/lib/python3.10/lib-dynload', '/home/patrick/.local/lib/python3.10/site-packages', '/usr/local/lib/python3.10/dist-packages', '/usr/lib/python3/dist-packages'], 'platform': 'linux', 'prefix': '/usr', 'real_prefix': None, 'stdout_encoding': 'utf-8', 'sysconfig': {'makefile_filename': '/usr/lib/python3.10/config-3.10-x86_64-linux-gnu/Makefile'}, 'sysconfig_paths': {'data': '{base}', 'include': '{installed_base}/include/python{py_version_short}{abiflags}', 'platlib': '{platbase}/{platlibdir}/python{py_version_short}/site-packages', 'platstdlib': '{platbase}/{platlibdir}/python{py_version_short}', 'purelib': '{base}/lib/python{py_version_short}/site-packages', 'scripts': '{base}/bin', 'stdlib': '{installed_base}/{platlibdir}/python{py_version_short}'}, 'sysconfig_scheme': 'posix_prefix', 'sysconfig_vars': {'PYTHONFRAMEWORK': '', 'abiflags': '', 'base': '/usr', 'installed_base': '/usr', 'platbase': '/usr', 'platlibdir': 'lib', 'py_version_short': '3.10'}, 'system_executable': '/usr/bin/python3.10', 'system_stdlib': '/usr/lib/python3.10', 'system_stdlib_platform': '/usr/lib/python3.10', 'version': '3.10.6 (main, Nov 14 2022, 16:10:14) [GCC 11.3.0]', 'version_info': VersionInfo(major=3, minor=10, micro=6, releaselevel='final', serial=0), 'version_nodot': '310'}) [virtualenv/discovery/py_info.py:435]
py39: 311 D discover exe from cache /usr - exact False: PythonInfo({'architecture': 64, 'base_exec_prefix': '/usr', 'base_prefix': '/usr', 'distutils_install': {}, 'exec_prefix': '/usr', 'executable': '/home/patrick/workspaces/myproject/.venv/bin/python3', 'file_system_encoding': 'utf-8', 'has_venv': True, 'implementation': 'CPython', 'max_size': 9223372036854775807, 'original_executable': '/usr/bin/python3.10', 'os': 'posix', 'path': ['/home/patrick/.local/pipx/venvs/tox/lib/python3.10/site-packages/virtualenv/discovery', '/usr/lib/python310.zip', '/usr/lib/python3.10', '/usr/lib/python3.10/lib-dynload', '/home/patrick/.local/lib/python3.10/site-packages', '/usr/local/lib/python3.10/dist-packages', '/usr/lib/python3/dist-packages'], 'platform': 'linux', 'prefix': '/usr', 'real_prefix': None, 'stdout_encoding': 'utf-8', 'sysconfig': {'makefile_filename': '/usr/lib/python3.10/config-3.10-x86_64-linux-gnu/Makefile'}, 'sysconfig_paths': {'data': '{base}', 'include': '{installed_base}/include/python{py_version_short}{abiflags}', 'platlib': '{platbase}/{platlibdir}/python{py_version_short}/site-packages', 'platstdlib': '{platbase}/{platlibdir}/python{py_version_short}', 'purelib': '{base}/lib/python{py_version_short}/site-packages', 'scripts': '{base}/bin', 'stdlib': '{installed_base}/{platlibdir}/python{py_version_short}'}, 'sysconfig_scheme': 'posix_prefix', 'sysconfig_vars': {'PYTHONFRAMEWORK': '', 'abiflags': '', 'base': '/usr', 'installed_base': '/usr', 'platbase': '/usr', 'platlibdir': 'lib', 'py_version_short': '3.10'}, 'system_executable': '/usr/bin/python3.10', 'system_stdlib': '/usr/lib/python3.10', 'system_stdlib_platform': '/usr/lib/python3.10', 'version': '3.10.6 (main, Nov 14 2022, 16:10:14) [GCC 11.3.0]', 'version_info': VersionInfo(major=3, minor=10, micro=6, releaselevel='final', serial=0), 'version_nodot': '310'}) [virtualenv/discovery/py_info.py:435]

```
Way too verbose to post completely.

## Minimal example

If possible, provide a minimal reproducer for the issue:

With this tox.ini:
```ini
[docker:dynamoDB]
image = amazon/dynamodb-local:latest
ports = 8000:8000/tcp

[testenv]
docker =
    dynamoDB
commands =
    pytest tests/ {posargs}
```

With tox 4.0.12:
```console
# docker ps
CONTAINER ID   IMAGE                          COMMAND                  CREATED         STATUS        PORTS                                       NAMES
d3c1a6403b59   amazon/dynamodb-local:latest   "java -jar DynamoDBL…"   2 seconds ago   Up 1 second   0.0.0.0:8000->8000/tcp, :::8000->8000/tcp   dynamoDB-tox-364494
```

With tox 4.0.13 and higher:
```console
# docker ps
CONTAINER ID   IMAGE                          COMMAND                  CREATED         STATUS         PORTS                                         NAMES
4de548f795c3   amazon/dynamodb-local:latest   "java -jar DynamoDBL…"   2 seconds ago   Up 2 seconds   0.0.0.0:32790->8000/tcp, :::32790->8000/tcp   dynamoDB-tox-363635
```
repo: tox-dev/tox
test_cmd: pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
test_patch: diff --git a/tests/config/loader/ini/test_factor.py b/tests/config/loader/ini/test_factor.py
index 00aa83c9..cec786b3 100644
--- a/tests/config/loader/ini/test_factor.py
+++ b/tests/config/loader/ini/test_factor.py
@@ -30,6 +30,7 @@ def complex_example() -> str:
     py, d: space
     extra: extra
     more-default
+    no:space
     """,
     )
 
@@ -73,6 +74,7 @@ def test_factor_env_filter(env: str, complex_example: str) -> None:
     assert "default" in result
     assert "lines" in result
     assert "more-default" in result
+    assert "no:space" in result
     if "py" in env:
         assert "py only" in result
         assert "not py" not in result