[Bugfix][Tool Parser] HY-V4 streaming: fix name boundary, drop nameless calls - #55550
[Bugfix][Tool Parser] HY-V4 streaming: fix name boundary, drop nameless calls#55550JoeyPatricio wants to merge 2 commits into
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Two bugs in the HYV4 streaming path, both in how the tool name is sliced
out of the buffer once the first <arg_key> or </tool_call> is seen.
1. Name boundary picks the wrong tag. arg_idx and end_idx are both
searched from start_idx, and the code preferred arg_idx whenever it
was not -1. When one delta carries an argument-less call followed by
a call with arguments, arg_idx points into the second call, so the
name slice runs through the first call's close:
<tool_call>get_time</tool_call><tool_call>get_weather<arg_key>...
streamed as a single call named "get_time</tool_call><tool_call>
get_weather", with get_time lost. The buffer restart three lines
down had the same preference and dropped the second call's opener,
attaching its arguments to the first. Both now use the nearer tag.
Single-token deltas never hit this; batched and speculative decode
deliver the whole sequence in one delta and do.
2. Empty function name is emitted. The name was set without checking
it was non-empty, so a malformed <tool_call> block with no name
produced a dispatchable tool call with name="" when streamed. The
strict non-streaming path already rejects the same output. Mirror
that guard: skip the malformed call once its closing tag arrives,
before current_tool_id is incremented so a following valid call
keeps its index.
Also add tests/tool_parsers/test_hy_v4_tool_parser.py, which had no
test module in the repo. It inherits the shared ToolParserTests suite
and adds HY-V4-specific coverage for suffix detection, strict and
non-strict extractor paths, schema-typed arguments, streaming state
mirroring, and single-delta batched tool calls.
test_malformed_input is xfailed for streaming because the shared
fixture reuses one parser across all malformed inputs; the unbalanced
<tool_call> input never closes its call, so the next input streams into
leaked state. Harness artifact only; vllm-project#51559 moves the suite to
per-request instances.
Co-authored-by: Claude <noreply@anthropic.com>
Signed-off-by: JoeyPatricio <joe.patricio@hotmail.com>
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WalkthroughThe HYV4 streaming extractor now preserves boundaries between adjacent calls and skips nameless calls. New tests cover tokenizer setup, suffix detection, argument typing, strictness, batched deltas, parser state, and shared parser behavior. ChangesHYV4 streaming parser
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: ⚪ Minimal · up to This change fixes HY-V4 streaming tool-call boundaries and skips completed nameless calls while preserving subsequent tool-call indexing. The reported parser tests and checks pass, with no concrete current-head merge-blocking risk identified. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Inline comments:
In `@tests/tool_parsers/test_hy_v4_tool_parser.py`:
- Around line 119-121: Parenthesize each of the four adjacent malformed-input
string groups in the relevant test data so Ruff ISC004 is resolved while each
complete payload remains a single list item. Update the malformed-input cases in
the test fixture without changing their contents or expected behavior.
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Ruff ISC004 (unparenthesized implicit string concatenation in a collection) flags the four multi-line malformed_input_outputs entries. The rule is newer than the ruff pinned in pre-commit, so it does not fail locally yet, but it will on the next ruff bump. Wrap each entry so the list-item boundaries are explicit, matching the other fixture strings in the same config. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: JoeyPatricio <joe.patricio@hotmail.com>
1 participant
Purpose
vllm/tool_parsers/hy_v4_tool_parser.pyis registered ashy_v4and is selectable byany user via
--tool-call-parser hy_v4. At the time of writing,grep -rl hy_v4 tests/returned nothing. No test module in the repo exercised it.
Adding that coverage surfaced two bugs in the streaming path, both in the few lines that
slice the tool name out of the buffer. This PR fixes both and adds the test module.
Bug 1: name boundary picks the wrong tag
Once a
<tool_call>start is buffered, the parser searches forward for the first<arg_key>and the first</tool_call>, both fromstart_idx:arg_idxwins whenever it is not-1, even whenend_idxis closer. When one deltacarries an argument-less call followed by a call with arguments,
arg_idxpoints intothe second call, and the name slice runs through the first call's closing tag. For:
streaming emitted one call named
get_time</tool_call><tool_call>get_weather, andget_timewas lost. The buffer restart three lines down had the same preference, soafter fixing
name_endalone the second call's opener was skipped and its argumentswere attached to
get_time.Both sites now use the nearer tag:
name_end = min(i for i in (arg_idx, end_idx) if i != -1)and
self._buffer = cur_text[name_end:].Single-token deltas never trigger this, which is why the shared suite's streaming tests
did not catch it. Batched and speculative decode deliver the whole
</tool_call><tool_call>name<arg_key>sequence in one delta and do.Bug 2: empty function name is emitted
The name was set without checking it was non-empty. For a malformed block:
the strict non-streaming path returns
tools_called=False(it raises"Empty function name in tool call."internally), while streaming emitted aDeltaToolCallwithfunction.name == "", which a client will attempt to dispatch.Same class of defect as #53539 in HY-V3.
The fix mirrors the strict guard: when the name is empty, skip the malformed call once
its closing tag has arrived. Two branches are needed because streaming sees partial text;
if
</tool_call>has not arrived yet the call is known to be bad but cannot be skipped,so it buffers and waits. The skip runs before
current_tool_id += 1, so a valid callfollowing a nameless one keeps its index.
Bug 1 also defeated this guard:
<tool_call></tool_call><tool_call>get_weather<arg_key>in one delta produced
tool_name = "</tool_call><tool_call>get_weather", which isnon-empty garbage, so the emptiness check never fired. Fixing bug 1 makes the guard
reliable.
Known limitations, not changed here
content=None, whereasnon-streaming returns the raw block as content. The malformed text is dropped rather
than surfaced. This is still strictly better than emitting a nameless call, but it is
not full parity.
<tool_call>(no closing tag), streaming emits a callwith unterminated argument JSON (
{"city": "Paris") via the existing end-of-outputhandling. Pre-existing and independent of this change; noted so it is not mistaken for
a regression.
_extract_tool_callspath has no empty-name guard. It is unreachable inserving because
HYV4ToolParserhardcodesstrict=True, and I did not want to widenthe diff into a path the adapter never takes.
Not a duplicate
Searches run against
vllm-project/vllm, open PRs:No open PR adds
hy_v4tests or touches either defect. The nearest neighbours aredistinct:
Related: #51706 adds a coverage ratchet requiring every registered parser to map to a
test module or sit in
PENDING_COVERAGE.hy_v4was registered in #54160 (2026-08-29),after that PR opened (2026-08-10), so it appears in neither its mapping nor its pending
list and would currently be flagged as unclassified. This PR closes that gap.
Test Plan
Test Result
New module:
The xfail is
test_malformed_input[True]. It is not a parser limitation: the sharedtool_parserfixture reuses one instance across all four malformed inputs, and theunbalanced-
<tool_call>input never closes its call, so the next input streams intoleaked
_streaming_tool_namestate and tripsStreamingToolReconstructor's id/indexassertions. With a fresh parser per input, none of the four raises. #51559 moves the
harness to per-request instances, which would remove the need for this mark. It is
strict, so it fails as XPASS the moment that happens.
Full directory, no collateral damage:
The 15 errors are pre-existing and unrelated. Every one is a setup error in
tests/tool_parsers/test_llama3_json_tool_parser.pyfrom a gated model download(
401 Unauthorizedformeta-llama/Llama-3.2-1B-Instruct). I confirmed all 15reproduce on this branch's base commit.
Bug 1 verified directly by feeding the entire output as a single delta, which is what
batched decode does:
get_time(no args) thenget_weather(city)get_time</tool_call><tool_call>get_weatherget_time,get_weather, arguments matching non-streamingget_weather(city)</tool_call><tool_call>get_weatherget_weatherwith{"city": "Tokyo"}Bug 2 verified directly, fresh parser per input, token-level deltas:
name=''get_weather, index 0get_weatherget_weatherget_weatherget_weather,search_hotelsLint:
On model evals
AGENTS.md asks for eval results on changes affecting output.
tests/evals/currentlyholds only model-level suites (
gsm8k,mrcr,gpt_oss,qwen4_exp), none of whichexercises tool-call parsing, so there is no eval to run for this change. The evidence
here is the unit coverage above, including the shared suite's streaming/non-streaming
agreement test and the new single-delta agreement tests, which are what a tool-parser
regression would trip. I am happy to run something specific if a reviewer wants it.
AI assistance
AI tooling (Claude Code) assisted with this change: exploring the parser, drafting the
test module, and drafting this description. A separate AI-assisted review pass found
bug 1 after the initial fix for bug 2 was written; I verified that finding against the
source before acting on it. The commit carries a matching
Co-authored-bytrailer. Ihave reviewed every changed line, ran the commands above myself, and can defend the
change in review.