LightningCLI fails loading jsonnet config files

[muthissar]

Bug description

jsonargparse supports jsonnet config files. LightningCli does not: Adding parser_kwargs={"parser_mode": "jsonnet"} and inputting a jsonnet file fails. This is caused by LightningCLI._dump_config not enforcing dumping to yaml.

I do not know if jsonnet is supposed to be supported by lightning, but the bug prevents silently using jsonnet with LightningCli. Adding format="yaml" to dump fixes issue, and I don't believe it's less general (since yaml.safe_load is used after).

What version are you seeing the problem on?

master

Reproduced in studio

No response

How to reproduce the bug

class MainModule(BoringModel):
        def __init__(self, main_param: int = 1):
            super().__init__()
            

    config = """{
        "model":{
            "main_param": 2
        }
    }"""
    config_path = Path("config.jsonnet")
    config_path.write_text(config)

    cli_args = [f"--config={config_path}"]
    with mock.patch("sys.argv", ["any.py"] + cli_args):
        cli = LightningCLI(MainModule, run=False, parser_kwargs={"parser_mode": "jsonnet"})

Error messages and logs

# Error messages and logs here please

Environment

Current environment

• CUDA:
  - GPU:
  - NVIDIA A40
  - NVIDIA A40
  - NVIDIA A40
  - NVIDIA A40
  - available: True
  - version: 12.6
• Lightning:
  - lightning-utilities: 0.14.3
  - pytorch-lightning: 2.5.1rc2
  - torch: 2.7.1
  - torchmetrics: 1.7.2
  - torchvision: 0.22.1
• Packages:
  - absl-py: 2.3.0
  - aiohappyeyeballs: 2.6.1
  - aiohttp: 3.12.12
  - aiosignal: 1.3.2
  - alabaster: 1.0.0
  - antlr4-python3-runtime: 4.9.3
  - anyio: 4.9.0
  - argon2-cffi: 25.1.0
  - argon2-cffi-bindings: 21.2.0
  - arrow: 1.3.0
  - asttokens: 3.0.0
  - async-lru: 2.0.5
  - attrs: 25.3.0
  - autocommand: 2.2.2
  - babel: 2.17.0
  - backcall: 0.2.0
  - backports.tarfile: 1.2.0
  - beautifulsoup4: 4.13.4
  - bitsandbytes: 0.46.0
  - black: 25.1.0
  - bleach: 6.2.0
  - certifi: 2025.4.26
  - cffi: 1.17.1
  - charset-normalizer: 3.4.2
  - click: 8.2.1
  - cloudpickle: 3.1.1
  - coloredlogs: 15.0.1
  - comm: 0.2.2
  - contourpy: 1.3.2
  - coverage: 7.8.2
  - curio: 1.6
  - cycler: 0.12.1
  - debugpy: 1.8.14
  - decorator: 5.2.1
  - deepspeed: 0.9.3
  - defusedxml: 0.7.1
  - docstring-parser: 0.16
  - docutils: 0.21.2
  - executing: 2.2.0
  - fastapi: 0.115.12
  - fastjsonschema: 2.21.1
  - filelock: 3.18.0
  - flatbuffers: 25.2.10
  - fonttools: 4.58.2
  - fqdn: 1.5.1
  - frozenlist: 1.7.0
  - fsspec: 2025.5.1
  - grpcio: 1.73.0
  - h11: 0.16.0
  - hjson: 3.1.0
  - httpcore: 1.0.9
  - httpx: 0.28.1
  - humanfriendly: 10.0
  - hydra-core: 1.3.2
  - idna: 3.10
  - imagesize: 1.4.1
  - importlib-metadata: 8.0.0
  - importlib-resources: 6.5.2
  - inflect: 7.3.1
  - iniconfig: 2.1.0
  - ipykernel: 6.29.5
  - ipyparallel: 9.0.1
  - ipython: 8.1.1
  - ipywidgets: 8.1.7
  - isoduration: 20.11.0
  - jaraco.collections: 5.1.0
  - jaraco.context: 5.3.0
  - jaraco.functools: 4.0.1
  - jaraco.text: 3.12.1
  - jedi: 0.19.2
  - jinja2: 3.1.6
  - joblib: 1.5.1
  - json5: 0.12.0
  - jsonargparse: 4.40.0
  - jsonnet: 0.21.0
  - jsonpointer: 3.0.0
  - jsonschema: 4.24.0
  - jsonschema-specifications: 2025.4.1
  - jupyter-client: 8.6.3
  - jupyter-core: 5.8.1
  - jupyter-events: 0.12.0
  - jupyter-lsp: 2.2.5
  - jupyter-server: 2.16.0
  - jupyter-server-terminals: 0.5.3
  - jupyterlab: 4.4.3
  - jupyterlab-pygments: 0.3.0
  - jupyterlab-server: 2.27.3
  - jupyterlab-widgets: 3.0.15
  - kiwisolver: 1.4.8
  - lightning-utilities: 0.14.3
  - markdown: 3.8
  - markdown-it-py: 3.0.0
  - markupsafe: 3.0.2
  - matplotlib: 3.10.3
  - matplotlib-inline: 0.1.7
  - mdurl: 0.1.2
  - mistune: 3.1.3
  - more-itertools: 10.3.0
  - mpmath: 1.3.0
  - multidict: 6.4.4
  - mypy-extensions: 1.1.0
  - nbclient: 0.10.2
  - nbconvert: 7.16.6
  - nbformat: 5.10.4
  - nest-asyncio: 1.6.0
  - networkx: 3.5
  - ninja: 1.11.1.4
  - notebook: 7.4.3
  - notebook-shim: 0.2.4
  - numpy: 2.3.0
  - nvidia-cublas-cu12: 12.6.4.1
  - nvidia-cuda-cupti-cu12: 12.6.80
  - nvidia-cuda-nvrtc-cu12: 12.6.77
  - nvidia-cuda-runtime-cu12: 12.6.77
  - nvidia-cudnn-cu12: 9.5.1.17
  - nvidia-cufft-cu12: 11.3.0.4
  - nvidia-cufile-cu12: 1.11.1.6
  - nvidia-curand-cu12: 10.3.7.77
  - nvidia-cusolver-cu12: 11.7.1.2
  - nvidia-cusparse-cu12: 12.5.4.2
  - nvidia-cusparselt-cu12: 0.6.3
  - nvidia-nccl-cu12: 2.26.2
  - nvidia-nvjitlink-cu12: 12.6.85
  - nvidia-nvtx-cu12: 12.6.77
  - omegaconf: 2.3.0
  - onnx: 1.18.0
  - onnxruntime: 1.22.0
  - outcome: 1.3.0.post0
  - overrides: 7.7.0
  - packaging: 25.0
  - pandas: 2.3.0
  - pandocfilters: 1.5.1
  - parso: 0.8.4
  - pathspec: 0.12.1
  - pexpect: 4.9.0
  - pickleshare: 0.7.5
  - pillow: 11.2.1
  - pip: 25.1
  - platformdirs: 4.3.8
  - pluggy: 1.6.0
  - prometheus-client: 0.22.1
  - prompt-toolkit: 3.0.51
  - propcache: 0.3.2
  - protobuf: 6.31.1
  - psutil: 7.0.0
  - ptyprocess: 0.7.0
  - pure-eval: 0.2.3
  - py-cpuinfo: 9.0.0
  - pycparser: 2.22
  - pydantic: 1.10.22
  - pygments: 2.19.1
  - pyparsing: 3.2.3
  - pytest: 8.4.0
  - pytest-asyncio: 1.0.0
  - pytest-cov: 6.1.1
  - pytest-random-order: 1.1.1
  - pytest-rerunfailures: 15.1
  - pytest-timeout: 2.4.0
  - python-dateutil: 2.9.0.post0
  - python-json-logger: 3.3.0
  - pytorch-lightning: 2.5.1rc2
  - pytz: 2025.2
  - pyyaml: 6.0.2
  - pyzmq: 26.4.0
  - qtconsole: 5.6.1
  - qtpy: 2.4.3
  - referencing: 0.36.2
  - requests: 2.32.4
  - rfc3339-validator: 0.1.4
  - rfc3986-validator: 0.1.1
  - rich: 14.0.0
  - roman-numerals-py: 3.1.0
  - rpds-py: 0.25.1
  - scikit-learn: 1.7.0
  - scipy: 1.15.3
  - send2trash: 1.8.3
  - setuptools: 78.1.1
  - six: 1.17.0
  - sniffio: 1.3.1
  - snowballstemmer: 3.0.1
  - sortedcontainers: 2.4.0
  - soupsieve: 2.7
  - sphinx: 8.2.3
  - sphinxcontrib-applehelp: 2.0.0
  - sphinxcontrib-devhelp: 2.0.0
  - sphinxcontrib-htmlhelp: 2.1.0
  - sphinxcontrib-jsmath: 1.0.1
  - sphinxcontrib-qthelp: 2.0.0
  - sphinxcontrib-serializinghtml: 2.0.0
  - stack-data: 0.6.3
  - starlette: 0.46.2
  - sympy: 1.14.0
  - tensorboard: 2.19.0
  - tensorboard-data-server: 0.7.2
  - tensorboardx: 2.6.4
  - terminado: 0.18.1
  - testpath: 0.6.0
  - threadpoolctl: 3.6.0
  - tinycss2: 1.4.0
  - tomli: 2.0.1
  - torch: 2.7.1
  - torchmetrics: 1.7.2
  - torchvision: 0.22.1
  - tornado: 6.5.1
  - tqdm: 4.67.1
  - traitlets: 5.14.3
  - trio: 0.30.0
  - triton: 3.3.1
  - typeguard: 4.3.0
  - types-python-dateutil: 2.9.0.20250516
  - typeshed-client: 2.7.0
  - typing-extensions: 4.14.0
  - tzdata: 2025.2
  - uri-template: 1.3.0
  - urllib3: 2.4.0
  - uvicorn: 0.34.3
  - wcwidth: 0.2.13
  - webcolors: 24.11.1
  - webencodings: 0.5.1
  - websocket-client: 1.8.0
  - werkzeug: 3.1.3
  - wheel: 0.45.1
  - widgetsnbextension: 4.0.14
  - yarl: 1.20.1
  - zipp: 3.19.2
• System:
  - OS: Linux
  - architecture:
  - 64bit
  - ELF
  - processor: x86_64
  - python: 3.13.4
  - release: 6.8.0-60-generic
  - version: Fix typo in README.md #63-Ubuntu SMP PREEMPT_DYNAMIC Tue Apr 15 19:04:15 UTC 2025

More info

No response