[Bugfix][Tool Parser] Handle non-finite numbers in coerce_to_schema_type

[ashishpatel26]

Purpose

vllm/tool_parsers/utils.py::coerce_to_schema_type() coerces
model-emitted tool-call argument strings to their JSON Schema type. It is
a shared helper used by a growing set of tool parsers (Qwen3 Coder,
MiniMax-M2, Step3, DeepSeek V3.2, Seed-OSS), so a defect here affects all
of them.

This PR fixes two issues with non-finite numeric values:

1. Uncaught OverflowError (crash). For a number-typed parameter the
   helper evaluated int(float(value)). When the model emits inf,
   -inf, Infinity, or a magnitude that overflows to infinity
   (e.g. 1e999), int(float("inf")) raises OverflowError. Only
   ValueError/TypeError were handled, so the exception propagated out
   of the calling tool parser.

2. Invalid JSON output. The final json.loads() fallback parsed
   1e999 into a float inf, which json.dumps() later renders as the
   invalid-JSON token Infinity, producing malformed tool-call arguments
   sent to the client.

Fix: reject non-finite floats in the number branch and in the
json.loads() fallback, preserving the raw string so the value stays
JSON-serializable and no exception is raised. Behavior for all finite
values is unchanged.

Reproduce (before this PR)

from vllm.tool_parsers.utils import coerce_to_schema_type
coerce_to_schema_type("inf", "number")     # OverflowError
coerce_to_schema_type("1e999", "number")   # OverflowError
coerce_to_schema_type("1e999", "integer")  # -> float inf -> json "Infinity"

Test Plan

Added a TestNonFiniteNumbers regression class to
tests/tool_parsers/test_utils.py covering inf, -inf, Infinity,
1e999, nan, -nan for both number and integer schema types,
asserting (a) no exception is raised and (b) the result round-trips
through json.dumps/json.loads (i.e. is valid, finite JSON).

python -m pytest tests/tool_parsers/test_utils.py -q
ruff check vllm/tool_parsers/utils.py tests/tool_parsers/test_utils.py
ruff format --check vllm/tool_parsers/utils.py tests/tool_parsers/test_utils.py

Test Result

• pytest tests/tool_parsers/test_utils.py → 70 passed (9 of the new
  cases fail on main before the fix, confirming the regression; all pass
  after).
• ruff check → All checks passed!
• ruff format --check → 2 files already formatted

Tests were run on a CPU-only build (VLLM_TARGET_DEVICE=empty).

Not a duplicate

Searched open/closed issues and PRs for coerce_to_schema_type. The
existing PRs (#43006, #43019, #43025, #43140, #43363) only adopt this
shared utility in additional parsers; none address non-finite numeric
input. No existing issue or PR covers this bug.

---

AI assistance was used to help investigate and implement this change. The
diff has been reviewed line by line and the tests were run locally with
the results shown above.

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[hclsys]

nice catch on both spots — the typed-number path and the json.loads fallback (1e999 -> inf) were independent leaks. math.isfinite guarding both, and falling through to string-passthrough, is consistent with the existing coerce("abc","number")=="abc" fallback contract, so no behavior surprise for callers.

tests cover inf/-inf/Infinity/nan/1e999 and assert json round-trip — thorough. lgtm from my read.

[ashishpatel26]

Pushed a follow-up commit (43fc116) that completes the fix by covering the same non-finite bug in the object/array branch.

json.loads accepts non-finite tokens, so the previously-unguarded object/array path still produced invalid JSON:

coerce_to_schema_type("[1e999]", "array")      # -> [inf]
coerce_to_schema_type('{"x": Infinity}', "object")  # -> {'x': inf}

Both re-serialize to invalid JSON ([Infinity] / {"x": Infinity}).

The commit adds a small _is_json_finite() helper (backed by json.dumps(..., allow_nan=False), which raises on any non-finite float anywhere in the structure) and uses it to guard both the object/array branch and the final json.loads() fallback. This supersedes the narrower scalar-float check and also catches non-finite floats nested inside parsed lists/dicts. Finite values are unchanged.

Added regression tests for arrays/objects containing 1e999/Infinity/-Infinity/NaN and the unknown-type fallback.

Local results: pytest tests/tool_parsers/test_utils.py → 80 passed; ruff check / ruff format --check clean (CPU-only VLLM_TARGET_DEVICE=empty build).

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @ashishpatel26.

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

[ashishpatel26]

Rebased onto the latest main and force-pushed — the conflict (from utils.py moving upstream) is resolved and the PR is now mergeable again. Tests still pass locally (pytest tests/tool_parsers/test_utils.py → 80 passed; ruff check and mypy-local clean).

[ashishpatel26]

👋 Hi maintainers — could someone please add the ready label to trigger CI? This contributor account has no merged PRs in vllm-project/vllm yet, so the pre-run-check gate requires a maintainer label. Fix reviewed locally, tests pass, DCO signed. Thank you!

[bbrowning]

I hit this in a live server testing our new streaming parser engine, which uses coerce_to_schema_type across several parsers. I applied this fix, and the errors went away.

The unit tests are well scoped, and exercise the change. I also ran a broader set of tests locally, including all the tests/parser/engine since those exercise this same path now. Everything passed.

Thanks for the contribution!