[alex-jw-brooks]

Purpose

Follow-up to #6291; rather than having a separate validate() function that we can call to get a list of errors, we should actually validate & raise an error if a PipelineConfig is not correctly configured. This will ensure that we do not accidentally create invalid PipelineConfig objects in vLLM Omni, and also is a better user experience when registering out of tree pipelines (i.e., PipelineConfig objects should explode as early as possible rather than deferring until we try to register it).

Errors surface as being joined by \n\t if there are more than one. E.g.,

from vllm_omni.config.stage_config import PipelineConfig, StagePipelineConfig

PipelineConfig(
    model_type="foobar",
    stages=[
        StagePipelineConfig(stage_id=0, model_stage="a"),
    ]
)

will raise

ValueError: PipelineConfig initialization failed with the following error(s): No terminal stage (stage with final_output=True)

from vllm_omni.config.stage_config import PipelineConfig, StagePipelineConfig

PipelineConfig(
    model_type="foobar",
    stages=[
        StagePipelineConfig(stage_id=0, model_stage="a"),
        StagePipelineConfig(stage_id=0, model_stage="a"),
    ]
)

will raise

ValueError: PipelineConfig initialization failed with the following error(s): 
        Duplicate stage IDs found
        No terminal stage (stage with final_output=True)

to try to keep it readable.

CC @lishunyang12 @m0g3r @hsliuustc0106 - PTAL, thanks!

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[vllm-omni-review-bot]

This PR appears to belong to: docs/design/module/vllm_omni_config.md.

Module owners: @lishunyang12 @alex-jw-brooks

@alex-jw-brooks, please review your own changes and leave a short self-review comment describing what you checked. PRs without author self-review may not be assigned a reviewer.

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[hsliuustc0106]

Two findings, both inlined:

• P1 (stage_config.py:306): eager validation raises for three test files the PR does not update — tests/config/test_pipeline_registry.py:33,44, tests/config/test_omni_config.py:1042,1072 (stageless constructions) and tests/utils/test_tracking_parser.py:33 (module-level pipeline with no final_output=True stage → whole-module collection error). No test lane ran on this PR, so the cpu lanes go red on merge. Fix: give these constructions a minimal terminal stage like SINGLE_STAGE_PIPE_CFG.
• P3 (stage_config.py:342): maybe_get_validation_errors_as_str is a single-caller helper — consider inlining into __post_init__.

Otherwise clean: verified there are no leftover .validate() callers and no in-tree production path constructs a PipelineConfig without stages, so the eager-fail design itself is safe in-tree.

[alex-jw-brooks]

Thanks @hsliuustc0106! I agree with your points. I inlined the helper and added the missing stage to other PipelineConfig calls, I think it's ready for another look when you have time!

[hsliuustc0106]

lgtm