[Core][V0] Enable regex support with xgrammar

[russellb]

We already support this in V1. This is just low hanging fruit to enable in V0 as well.

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[terrytangyuan]

Would it be a good idea to check xgrammar version and print out warning if they are using an old version?

[russellb]

Would it be a good idea to check xgrammar version and print out warning if they are using an old version?

hm, I'm not sure we do that other places. We just assume the code has what we express is required in the requirements files. You're on your own if you veer outside of that!

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @russellb.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[Ubospica]

I think it should work fine with xgrammar. Thanks @russellb !

[russellb]

marked as a draft again as the pin to 0.1.11 is intentional to avoid a bug introduced in 0.1.13. I'll revisit this again after a release that resolves the bug in question.

#13338

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @russellb.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[russellb]

This should be ready now

[aarnphm]

superseded by #14868

[simon-mo]

Removing this from v0.8.0 because it is not a bugfix. We will release another version soon for features.

[aarnphm]

wfm. we can have more time to fix bugs instead of rushing it in.

[Copilot]

Pull Request Overview

This PR enables regex support in xgrammar by updating the grammar configuration and modifying the guided decoding logic. Key changes include adding a new regex_str field to GrammarConfig, adding a branch to handle regex-guided decoding in from_guided_params and _ensure_ctx, and updating test cases and fallback logic accordingly.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
vllm/model_executor/guided_decoding/xgrammar_decoding.py	Adds regex_str to configuration, handles regex-guided decoding in from_guided_params and _ensure_ctx
vllm/model_executor/guided_decoding/init.py	Removes fallback check for regex support in favor of JSON validation
tests/entrypoints/llm/test_guided_generate.py	Updates tests to verify failure when unsupported JSON schema features are provided

Comments suppressed due to low confidence (1)

vllm/model_executor/guided_decoding/xgrammar_decoding.py:253

• To prevent ambiguity when multiple guided decoding options are provided, consider validating that only one of grammar, json, or regex is set in guided_params.

elif guided_params.regex:

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @russellb.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[Ubospica]

Thanks for your awesome work! @russellb @aarnphm @simon-mo @DarkLight1337