[Plugin] Simplify IO Processor Plugin interface

[DarkLight1337]

Purpose

• Rename parse_request -> parse_data and pass request.data to it so there is no need to distinguish between offline and online APIs.
• For the same reason, deprecate output_to_response, since we can construct the response automatically from the output data and provided request ID.
• Split up validate_or_generate_params into merge_sampling_params and merge_pooling_params to make type annotation easier.

All changes are back-compatible until v0.19.

cc @maxdebayser @christian-pinto

Test Plan

Test Result

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
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[mergify]

Documentation preview: https://vllm--34236.org.readthedocs.build/en/34236/

[gemini-code-assist]

Code Review

This pull request simplifies the IOProcessor plugin interface by renaming parse_request to parse_data, deprecating output_to_response, and splitting validate_or_generate_params. The changes are aimed at unifying the online and offline APIs and improving type annotations, with backward compatibility in mind. However, I've identified a critical issue where removing request_id from the post_process method signature breaks the ability for plugins to maintain context between pre-processing and post-processing steps for a given request.

[DarkLight1337]

/gemini review

[gemini-code-assist]

Code Review

This pull request simplifies the IOProcessor plugin interface by renaming, deprecating, and splitting methods for better clarity and type safety. The changes are well-documented and applied to the test plugin. However, I've identified a critical issue with the backward compatibility shims for merge_sampling_params and merge_pooling_params. These shims are not type-safe and could lead to runtime errors by returning objects of an incorrect type. I've included suggestions to make these shims robust and ensure true backward compatibility.

[mergify]

Hi @DarkLight1337, 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

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[christian-pinto]

Thanks @DarkLight1337, let me run a few tests.

[maxdebayser]

This is nice, letting the plugin decide which task it will be instead of just setting "plugin". This is useful for plugins that just want to post process the output for existing tasks, for example.

[noooop]

PTAL #34214

We need to make the renderer easily accessible to the IO Processor.

[maxdebayser]

We need to make the renderer easily accessible to the IO Processor.

I was about to make the same comment :)

[DarkLight1337]

Yeah, this is the first step towards making that happen. I am planning to initialize IOProcessor and use it to process the input prompt regardless of plugin, with the default one being a no-op. Then plugins can have their custom IOProcessor subclass.

[mergify]

Hi @DarkLight1337, 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