Chain with a single task group

[edwardreed81]

Checklist

• I have verified that the issue exists against the main branch of Celery.
• This has already been asked to the discussions forum first.
• I have read the relevant section in the
  contribution guide
  on reporting bugs.
• I have checked the issues list
  for similar or identical bug reports.
• I have checked the pull requests list
  for existing proposed fixes.
• I have checked the commit log
  to find out if the bug was already fixed in the main branch.
• I have included all related issues and possible duplicate issues
  in this issue (If there are none, check this box anyway).
• I have tried to reproduce the issue with pytest-celery and added the reproduction script below.

Mandatory Debugging Information

• I have included the output of celery -A proj report in the issue.
  (if you are not able to do this, then at least specify the Celery
  version affected).
• I have verified that the issue exists against the main branch of Celery.
• I have included the contents of pip freeze in the issue.
• I have included all the versions of all the external dependencies required
  to reproduce this bug.

Optional Debugging Information

• I have tried reproducing the issue on more than one Python version
  and/or implementation.
• I have tried reproducing the issue on more than one message broker and/or
  result backend.
• I have tried reproducing the issue on more than one version of the message
  broker and/or result backend.
• I have tried reproducing the issue on more than one operating system.
• I have tried reproducing the issue on more than one workers pool.
• I have tried reproducing the issue with autoscaling, retries,
  ETA/Countdown & rate limits disabled.
• I have tried reproducing the issue after downgrading
  and/or upgrading Celery and its dependencies.

Related Issues and Possible Duplicates

Related Issues

• None

Possible Duplicates

• None

Environment & Settings

Celery version: 5.3.6 (emerald-rush)

celery report Output:

software -> celery:5.3.6 (emerald-rush) kombu:5.3.6 py:3.11.8
            billiard:4.2.0 py-amqp:5.2.0
platform -> system:Linux arch:64bit, ELF
            kernel version:6.1.66-1-lts imp:CPython
loader   -> celery.loaders.app.AppLoader
settings -> transport:amqp results:db+sqlite:///None

result_backend: 'db+sqlite:///None'
task_serializer: 'pickle'
result_serializer: 'pickle'
accept_content: ['pickle', 'json']
deprecated_settings: None

Steps to Reproduce

Required Dependencies

• Minimal Python Version: N/A or Unknown
• Minimal Celery Version: N/A or Unknown
• Minimal Kombu Version: N/A or Unknown
• Minimal Broker Version: N/A or Unknown
• Minimal Result Backend Version: N/A or Unknown
• Minimal OS and/or Kernel Version: N/A or Unknown
• Minimal Broker Client Version: N/A or Unknown
• Minimal Result Backend Client Version: N/A or Unknown

Python Packages

pip freeze Output:

amqp==5.2.0
annotated-types==0.6.0
anyio==4.3.0
argon2-cffi==23.1.0
argon2-cffi-bindings==21.2.0
arrow==1.3.0
asciitree==0.3.3
asttokens==2.4.1
async-lru==2.0.4
attrs==23.2.0
autograd==1.6.2
autograd-gamma==0.5.0
Babel==2.14.0
beautifulsoup4==4.12.3
bidict==0.23.1
billiard==4.2.0
bleach==6.1.0
Bottleneck==1.3.8
celery==5.3.6
certifi==2024.2.2
cffi==1.16.0
charset-normalizer==3.3.2
click==8.1.7
click-didyoumean==0.3.1
click-plugins==1.1.1
click-repl==0.3.0
cloudpickle==3.0.0
comm==0.2.1
contourpy==1.2.1
cycler==0.12.1
dask==2024.4.0
debugpy==1.8.1
decorator==5.1.1
defusedxml==0.7.1
dnspython==2.6.1
dotmap==1.3.30
email_validator==2.1.1
et-xmlfile==1.1.0
executing==2.0.1
fastapi==0.109.2
fasteners==0.19
fastjsonschema==2.19.1
fonttools==4.50.0
formulaic==1.0.1
fqdn==1.5.1
fsspec==2024.3.1
future==1.0.0
greenlet==3.0.3
h11==0.14.0
httpcore==1.0.4
httpx==0.27.0
idna==3.6
importlib_metadata==7.1.0
interface-meta==1.3.0
ipykernel==6.29.3
ipython==8.22.2
isoduration==20.11.0
jedi==0.19.1
Jinja2==3.1.3
joblib==1.3.2
json5==0.9.21
jsonpointer==2.4
jsonschema==4.21.1
jsonschema-specifications==2023.12.1
jupyter-events==0.9.0
jupyter-lsp==2.2.4
jupyter_client==8.6.0
jupyter_core==5.7.1
jupyter_server==2.13.0
jupyter_server_terminals==0.5.2
jupyterlab==4.1.3
jupyterlab_pygments==0.3.0
jupyterlab_server==2.25.3
kiwisolver==1.4.5
kombu==5.3.6
lifelines==0.28.0
llvmlite==0.42.0
locket==1.0.0
MarkupSafe==2.1.5
matplotlib==3.8.4
matplotlib-inline==0.1.6
mistune==3.0.2
msgpack==1.0.8
nbclient==0.9.0
nbconvert==7.16.2
nbformat==5.9.2
nest-asyncio==1.6.0
notebook_shim==0.2.4
numba==0.59.0
numcodecs==0.12.1
numpy==1.26.4
openpyxl==3.1.2
orjson==3.9.15
overrides==7.7.0
packaging==23.2
pandas==2.2.1
pandocfilters==1.5.1
parso==0.8.3
partd==1.4.1
pexpect==4.9.0
pillow==10.3.0
platformdirs==4.2.0
plotly==5.19.0
prometheus_client==0.20.0
prompt-toolkit==3.0.43
psutil==5.9.8
psycopg2-binary==2.9.9
ptyprocess==0.7.0
pure-eval==0.2.2
pyarrow==15.0.2
pycparser==2.21
pydantic==2.6.4
pydantic-extra-types==2.6.0
pydantic_core==2.16.3
Pygments==2.17.2
pyparsing==3.1.2
python-dateutil==2.9.0.post0
python-engineio==4.9.0
python-json-logger==2.0.7
python-socketio==5.11.2
pytz==2024.1
PyYAML==6.0.1
pyzmq==25.1.2
referencing==0.33.0
requests==2.31.0
rfc3339-validator==0.1.4
rfc3986-validator==0.1.1
rpds-py==0.18.0
scipy==1.13.0
Send2Trash==1.8.2
simple-websocket==1.0.0
six==1.16.0
sniffio==1.3.1
soupsieve==2.5
SQLAlchemy==2.0.28
sqlmodel==0.0.16
stack-data==0.6.3
starlette==0.36.3
tenacity==8.2.3
terminado==0.18.0
tinycss2==1.2.1
toolz==0.12.1
tornado==6.4
tqdm==4.66.2
traitlets==5.14.1
typer==0.9.4
types-python-dateutil==2.8.19.20240106
typing_extensions==4.10.0
tzdata==2024.1
uri-template==1.3.0
urllib3==2.2.1
uvicorn==0.27.1
vine==5.1.0
wcwidth==0.2.13
webcolors==1.13
webencodings==0.5.1
websocket-client==1.7.0
wrapt==1.16.0
wsproto==1.2.0
xarray==2024.2.0
zarr==2.17.1
zipp==3.18.1
zstandard==0.22.0

Other Dependencies

N/A

Minimally Reproducible Test Case

run_tasks = [run_task(...).s() for task in tasks]
chain = setup_task(...).s() | group(run_tasks)
result = chain.apply_async()

Expected Behavior

If tasks is length 1, result is type GroupResult

Actual Behavior

If tasks is length 1, result is type AsyncResult

It seems as though adding the group to a chain changes the group into a standalone task if there's only one task in the group.