[Misc] Fix Current vLLM config is not set. warnings, assert to avoid issues in the future

[LucasWilkinson]

#30531 and #29575 introduced accesses to get_current_vllm_config on boot that are outside of set_current_vllm_config contexts leading to repeated logs

(EngineCore_DP0 pid=1647618) WARNING 01-05 16:41:49 [vllm.py:1447] Current vLLM config is not set.
(EngineCore_DP0 pid=1647618) INFO 01-05 16:41:49 [scheduler.py:231] Chunked prefill is enabled with max_num_batched_tokens=2048.
(EngineCore_DP0 pid=1647618) INFO 01-05 16:41:49 [vllm.py:635] Disabling NCCL for DP synchronization when using async scheduling.
(EngineCore_DP0 pid=1647618) INFO 01-05 16:41:49 [vllm.py:640] Asynchronous scheduling is enabled.
(EngineCore_DP0 pid=1647618) INFO 01-05 16:41:49 [dp_utils.py:30] Using CPU all reduce to synchronize DP padding between ranks.

when get_current_vllm_config falls back to creating a default config. This also lead to slight config propagation bugs as some custom ops would see the default config instead of the real one.

This PR fixes those accesses and makes it an assert to try to avoid this in the future.

Longer term we should consider something like: #30859

TODO: get CI green with targeted additions of VLLM_ALLOW_DEFAULT_CONFIG

[gemini-code-assist]

Code Review

This pull request improves the robustness of the vLLM configuration handling by replacing a warning with an assertion when the configuration is not set. This helps to catch potential bugs early. An environment variable VLLM_ALLOW_DEFAULT_CONFIG is introduced to maintain the old behavior for testing purposes, which is a thoughtful addition.

The other changes in the pull request are logical consequences of this stricter configuration check. The use of a lazy dictionary in vllm/model_executor/layers/fused_moe/cpu_fused_moe.py correctly defers the instantiation of CustomOp subclasses until they are needed, avoiding errors during module import. Similarly, caching the GroupedTopk instance in vllm/model_executor/layers/fused_moe/layer.py is a good optimization that also resolves the configuration access issue.

Overall, the changes are well-implemented, improve code quality, and I have no concerns.

[mergify]

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[ProExpertProg]

Thanks for addressing this!

[mergify]

Hi @LucasWilkinson, the pre-commit checks have failed. Please run:

uv pip install pre-commit
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[mergify]

Hi @LucasWilkinson, the pre-commit checks have failed. Please run:

uv pip install pre-commit
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.

Tip

Is mypy or markdownlint failing?

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# For mypy (substitute "3.10" with the failing version if needed)
pre-commit run --hook-stage manual mypy-3.10
# For markdownlint
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[ProExpertProg]

Just a nit for the error message, thanks for this cleanup!

[mergify]

Hi @LucasWilkinson, the pre-commit checks have failed. Please run:

uv pip install pre-commit
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.

Tip

Is mypy or markdownlint failing?

mypy and markdownlint are run differently in CI. If the failure is related to either of these checks, please use the following commands to run them locally:

# For mypy (substitute "3.10" with the failing version if needed)
pre-commit run --hook-stage manual mypy-3.10
# For markdownlint
pre-commit run --hook-stage manual markdownlint

[nvpohanh]

Thanks for fixing this! Really appreciate it