[Bugfix] Fix lfm2 tool parser dropping calls with brackets or newline… by fatday · Pull Request #48171 · vllm-project/vllm

fatday · 2026-07-09T21:30:17Z

[Bugfix] Fix lfm2 tool parser dropping or corrupting recoverable tool calls

Purpose

The lfm2 pythonic tool parser silently drops (or corrupts) tool calls for a
range of outputs that real agentic models emit routinely. Each commit fixes one
failure class, with the model output that triggered it:

Model output	Before this PR	After this PR
`command='grep -F "]" log.txt'` (bracket in string)	bracket stack corrupted, call dropped (streaming)	parsed; `{"command": "grep -F \"]\" log.txt"}`
`command='cat > f.py << EOF\n...'` (raw newline in string)	`ast.parse` fails, call dropped (both paths)	parsed; value keeps the raw newlines exactly
`content='pattern \\'` (string ends in backslash)	quote-state misread, call dropped (streaming)	parsed; value ends in the literal backslash
`longitude=-74.0046539` (negative number)	`UnaryOp` rejected, call dropped	parsed; `{"longitude": -74.0046539}`
`size=(800, 600)` (tuple)	no JSON tuple type, call dropped	parsed; `{"size": [800, 600]}`
`memory_get(from=1)` (reserved-keyword parameter)	`SyntaxError`, call dropped	parsed; `{"from": 1}` (original name restored)
`<\|tool_call_start\|> [...` (whitespace after sentinel)	`IndentationError`, call dropped (streaming only)	parsed in both paths
`command='printf a\x00b'` (NUL byte)	`ValueError` (not `SyntaxError`), call dropped / truncated args	parsed; `{"command": "printf a\u0000b"}`
`msg=f'hello'` (placeholder-free f-string)	`JoinedStr` rejected, call dropped	parsed; `{"msg": "hello"}`
`tags={'urgent', 'bug'}` (set)	rejected, call dropped / truncated args	parsed; `{"tags": ["urgent", "bug"]}`
`[]` (empty block)	`tools_called=True` with zero calls	`tools_called=False`, no phantom tool-call turn
`month=07` (zero-padded int)	`SyntaxError`, call dropped	parsed; `{"month": 7}`
`command='sed -n '360,450p' f.py'` (nested quotes)	juxtaposition `SyntaxError`, call dropped / truncated invalid-JSON stream	parsed; value keeps the inner quotes exactly
`command='python3 -c "...x='\,'..."'` (doubly nested `-c` payload)	`SyntaxError`, call dropped / corrupted streamed args	parsed when exactly one closing quote yields parseable text (ast-validated); streaming withholds deltas while a string is broken
`x=b'abc'` / `...` / `1j`	`TypeError` inside `json.dumps` drops all sibling calls	rejected cleanly via `UnexpectedAstError`, like other unsupported nodes

All recovery rewrites are no-ops on input that already parses, and every
recovered argument value round-trips exactly (escapes evaluate back to the
original control chars).

Scope: control-char escaping is applied at the lfm2 call sites, not inside
the shared make_valid_python, so the streaming behavior of the other pythonic
parsers (pythonic, llama4_pythonic, olmo3) is unchanged. The literal-type
additions in get_parameter_value (negatives, tuples, sets, constant
f-strings) are shared with those parsers by design — same as the existing
handling for JSON name literals — and their test suites pass unchanged.

Related: #46708 touches the same function but fixes a different edge case
(backslash-run counting before a closing quote); no overlap.

Test Plan

pytest tests/tool_parsers/test_utils.py -v
pytest tests/tool_parsers/test_lfm2_tool_parser.py -v
pytest tests/tool_parsers/test_pythonic_tool_parser.py \
       tests/tool_parsers/test_llama4_pythonic_tool_parser.py \
       tests/tool_parsers/test_olmo3_tool_parser.py

Every failure class has a utils-level regression test plus streaming and
non-streaming end-to-end cases through the lfm2 parser.

Test Result

tests/tool_parsers/test_utils.py: 174 passed
tests/tool_parsers/test_lfm2_tool_parser.py: 45 passed
pythonic / llama4_pythonic / olmo3 suites: 60 passed (unchanged)
ruff check / ruff format (v0.14.0) and mypy 1.20.2 (repo config): clean

github-actions · 2026-07-09T21:30:26Z

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…s in string args Two failure modes in pythonic tool-call parsing, both hit by agentic models emitting shell commands as string arguments: 1. make_valid_python counted brackets inside string literals, so a bracket in a quoted argument (e.g. exec(command='grep -F "]" log.txt')) corrupted the bracket stack and the streaming parse raised UnexpectedAstError, dropping the call. Skip brackets while inside a string literal; only an unescaped matching quote closes it. 2. A raw newline inside a string argument (multi-line shell command / heredoc) is invalid Python, so ast.parse failed with 'unterminated string literal' and the whole call was dropped, both in extract_tool_calls and in the streaming path's final parse. Add escape_ctrl_chars_in_strings, which escapes \n/\r/\t only inside string literals, and retry the parse with the escaped text; the argument value round-trips exactly. On LiveClawBench with LFM2.5-based agents these two together dropped ~8% of tool calls (every multi-line command). Co-authored-by: Claude (Anthropic) <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

make_valid_python decided whether a quote closed its enclosing string by inspecting only the single preceding character for a backslash. That is wrong for an even run of backslashes: in `content='...\\'` the closing quote follows an escaped backslash (`\\`), so it DOES close the string -- but the single-char check read it as an escaped quote, left the string open, and returned None, silently dropping the tool call. Hits code/regex arguments (e.g. `r'\b'`) whose value ends in a backslash. Decide escaping by backslash parity via a small `_is_escaped` helper: a character is escaped iff preceded by an odd number of backslashes. Odd runs (a genuinely escaped quote) still keep the string open; even runs close it. On our internal agentic trace corpus this removed the streaming-only residual (16 -> 2 dropped tool calls across 1.15M), bringing the streaming path to parity with the non-streaming path. Co-authored-by: Claude (Anthropic) <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

A negative number is parsed by Python as ast.UnaryOp(USub, Constant(n)) rather than a plain Constant, so get_parameter_value rejected it and the whole tool-call list was dropped. Negative longitudes, deltas, and offsets are common tool arguments; a scan of ~5.9M markers across four datasets found 30,217 dropped calls, all caused by this (up to 34.6% of rows in one set). Add a branch that unwraps unary +/- over a numeric constant, at any nesting depth, restricted to numeric operands so genuine non-literals still raise. Purely additive: no input that parsed before changes behavior. Co-authored-by: Claude (Anthropic) <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

A tuple argument (e.g. size=(800, 600)) parsed as ast.Tuple, which get_parameter_value did not handle, so the whole tool-call list was dropped. JSON has no tuple type; decode it as a list so it round-trips through json.dumps. Matches the behavior of the BFCL liquid_api handler. Co-authored-by: Claude (Anthropic) <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

Tools legitimately name parameters `from`, `in`, `class` — but `memory_get(from=1)` is a Python SyntaxError no escape retry can recover, so the whole tool-call list was dropped (observed in real traces). Add rename_reserved_kwargs, a string-aware scanner that rewrites `from=` to `from_pyreservedkw_=` only outside string literals and only in keyword-argument position (preceded by `(` or `,`, followed by a single `=`), plus restore_reserved_kwarg_names as its exact inverse applied to the decoded arguments. Wired into both lfm2 paths: non-streaming as a third recovery attempt after the control-char escape retry, streaming as a deterministic pre-rewrite so successive chunks stay consistent. Inputs that parsed before take an identical code path. Co-authored-by: Claude (Anthropic) <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

… rename Python permits a newline between a keyword-argument name and its `=` inside parens (`memory_get(from\n=1)`), but rename_reserved_kwargs skipped only spaces/tabs in its lookahead, so the rename never fired and the call was still dropped. Skip all whitespace; the `(`/`,` position guard and `==` exclusion are unchanged. Co-authored-by: Claude (Anthropic) <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

…fm2 parser The escaped-retry inside make_valid_python changed streaming behavior for every consumer of the shared helper (pythonic, llama4_pythonic, olmo3), making their streaming paths accept raw newlines that their non-streaming paths still reject. Move the escape to the lfm2 streaming call site, next to the existing reserved-keyword rewrite, so the shared helper keeps its upstream semantics and the recovery stays scoped to the parser whose models are known to emit raw control chars in string arguments. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

…path Whitespace between <|tool_call_start|> and the opening bracket made every streaming completion candidate an IndentationError, so the call was silently dropped while the non-streaming path (which strips the tool text) parsed it fine. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

ast.parse rejects a NUL byte anywhere in the source with ValueError, not SyntaxError, so the escape-retry chain never fired: the call was dropped in non-streaming mode and streaming emitted truncated arguments. Escape NUL inside string literals alongside the other control chars and widen the retry to catch ValueError. Observed in production: LFM2 emitting printf/shell commands with embedded NULs. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

Python parses f'hello' as JoinedStr, not Constant, so get_parameter_value rejected it and the whole call was dropped even though the value is a plain string constant. Fold all-Constant JoinedStr parts; f-strings with real placeholders still raise. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

JSON has no set type; decode a set argument (tags={'urgent', 'bug'}) as a list in source order, mirroring the tuple handling, instead of dropping the whole call. make_valid_python keeps rejecting Set nodes only when its own completion added the closing brace (the truncated-dict artifact it was guarding against); a set the model closed itself now parses. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

…alled An empty block ([]) passed the all()-over-elts check vacuously and returned tools_called=True with zero tool calls, breaking the tools_called == bool(tool_calls) invariant the test helpers assert. Require at least one element; an empty block now falls back to content. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

month=07 is a SyntaxError (leading zeros in decimal integer literals) that neither the escape nor the rename retry can recover, so the whole call was dropped. Add a quote-aware rewrite that strips leading zeros from decimal int literals outside string literals, leaving already-valid tokens (0x/0o/0b, floats, exponents, all-zero literals, fractional parts) untouched. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

bytes/Ellipsis/complex are ast.Constant nodes, so they passed get_parameter_value and only failed later as a TypeError inside json.dumps. Restrict the Constant branch to JSON-representable types and raise UnexpectedAstError with a warning like the other unsupported nodes. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

mypy (pinned 1.20.2, repo config) flagged the ast.parse(...).body[0].value chains as attr-defined errors on ast.stmt. Replace them with shared _first_call/_bare_call/_kwarg_constant helpers that narrow via isinstance, deduplicating the inline chains. Test behavior unchanged. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

…otes Shell commands nest unescaped same-style quotes inside string arguments — command='sed -n '360,450p' f.py', or a quoted python3 -c payload whose code contains its own quoted strings. Python reads these as juxtaposed garbage, so the call was dropped (non-streaming) or streamed as truncated or corrupted arguments — high-frequency patterns in SWE-agent traces. A string is treated as broken when its first unescaped quote cannot syntactically close it. For a broken string, every syntactically plausible closing quote is tried (interior quotes escaped, rest of the text verbatim) and validated with ast.parse; exactly one parsing candidate means recovery with the exact value the model wrote, anything else is left unchanged rather than guessed at. Applied as a last-resort rewrite after the existing recoveries, only to text that failed to parse. Streaming additionally withholds tool deltas while the partial text contains a broken string (contains_broken_string_literal): any completion-based parse of such text is an implicit-concatenation misreading whose streamed prefix could never be retracted. The recovery then runs once the end sentinel arrives, on final text. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

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fatday · 2026-08-06T16:35:56Z

@chaunceyjiang Hi! This PR extends the lfm2 tool parser you merged in #39243. Real agentic traces (SWE-agent / OpenClaw-style shell commands) hit a range of outputs the parser silently drops or corrupts — nested quotes (sed -n '1,9p'), raw newlines, NUL bytes, negative numbers, tuples, reserved-keyword parameters, etc. Each commit fixes one failure class with regression tests (174 utils + 45 e2e; the pythonic/llama4/olmo3 suites pass unchanged).

github-actions · 2026-08-10T01:16:22Z

✅ @fatday, CI is now available for this PR.

/ci run starts a CI build.
/ci retry retries failed jobs in the CI build for the current PR head. If the current head has no CI build, it starts a new CI build for the current head containing only jobs that failed in the latest earlier CI build for this PR.

chaunceyjiang · 2026-08-10T01:16:22Z

/ci run

github-actions · 2026-08-10T01:16:38Z

✅ Triggered Buildkite CI #83076 for commit 9644abf76add.

fatday · 2026-08-10T04:29:03Z

/ci run

github-actions · 2026-08-10T04:29:19Z

✅ Triggered Buildkite CI #83092 for commit 2511d705b292.

chaunceyjiang

LGTM

vllm-project#48171) Signed-off-by: Zetian Li <804561096@qq.com> Co-authored-by: Claude (Anthropic) <noreply@anthropic.com>

…eady parses Adjacent string literals ('ab' 'cd') are valid Python that concatenates to one value, and the non-streaming path returns it. The broken-string guard I added in vllm-project#48171 misreads the second opening quote as a string that cannot be closed and withholds every later delta -- including the final, fully parseable text -- so the client is left holding a truncated argument ({"s": "ab from [f(s='ab' 'cd')]) that never becomes valid JSON. Text that parses has no broken string to wait for: run the guard only while ast.parse fails, which is the only state the requote recovery it protects can act on anyway. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

…block completion Completing a partial streaming block can fabricate a value the model has not finished writing: closing f' yields f'' (an empty constant f-string) and closing a just-opened [ yields an empty list. Both convert, so the call's argument prefix is streamed -- and when the real value arrives (a placeholder, a comprehension) the call stops converting and is dropped, leaving the client a tool call whose arguments are half a JSON object: [g(ok=1), f(x=f'{q}')] -> g {"ok": 1} f {"x": " [g(ok=1), f(x=[i for i in y])] -> g {"ok": 1} f {"x": [ Make make_valid_python treat both shapes as incomplete: a string still open at the end of the text whose prefix contains f, and a list anywhere but directly after a closed call. Nothing fabricated converts, so nothing is streamed that may need to be retracted; the unconvertible call is skipped whole and the sibling still comes through. The f-string half is a regression I introduced in vllm-project#48171 (before the constant-f-string support added there, f'' did not convert and nothing was streamed); the list half predates it. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zetian Li <804561096@qq.com>

…or NUL bytes A raw newline inside a string argument (multi-line shell commands are routine in LFM2 agentic traces) is invalid Python, and a NUL byte anywhere makes ast.parse raise ValueError rather than SyntaxError, so the whole call was dropped although the intent is unambiguous. Escape control chars inside string literals only and retry the parse; the escape sequences evaluate back to the exact original value. This introduces the recovery loop that later commits extend with more rewrites, each a no-op on already-valid text. Mirrors vllm-project/vllm#48171. Co-authored-by: Claude <noreply@anthropic.com>

mergify Bot added tool-calling bug Something isn't working labels Jul 9, 2026

github-project-automation Bot added this to Tool Calling Jul 9, 2026

NishchayMahor mentioned this pull request Jul 27, 2026

[Bugfix] Fix llama3_json parser dropping parallel and prose-adjacent tool calls #49923

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fatday force-pushed the fix-lfm2-tool-parser-string-literals branch 3 times, most recently from 846d5fa to 6c82bdb Compare August 4, 2026 10:58

fatday and others added 15 commits August 4, 2026 23:44

fatday force-pushed the fix-lfm2-tool-parser-string-literals branch from 3695c8a to bdf7db6 Compare August 4, 2026 23:45

fatday force-pushed the fix-lfm2-tool-parser-string-literals branch from bdf7db6 to b1c3fad Compare August 5, 2026 00:10

Merge branch 'main' into fix-lfm2-tool-parser-string-literals

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fatday marked this pull request as ready for review August 6, 2026 10:12

fatday requested review from aarnphm and chaunceyjiang as code owners August 6, 2026 10:12

fatday requested review from bbrowning and sfeng33 as code owners August 6, 2026 10:12

claude Bot reviewed Aug 6, 2026

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fatday added 3 commits August 7, 2026 13:15

Merge branch 'main' into fix-lfm2-tool-parser-string-literals

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Merge branch 'main' into fix-lfm2-tool-parser-string-literals

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Merge branch 'main' into fix-lfm2-tool-parser-string-literals

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chaunceyjiang added verified Run pre-commit for new contributors without triggering other tests ready ONLY add when PR is ready to merge/full CI is needed labels Aug 10, 2026

Merge branch 'main' into fix-lfm2-tool-parser-string-literals

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chaunceyjiang approved these changes Aug 10, 2026

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chaunceyjiang merged commit 7303c66 into vllm-project:main Aug 10, 2026
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github-project-automation Bot moved this to Done in Tool Calling Aug 10, 2026

fatday mentioned this pull request Aug 10, 2026

[Fix] lfm2 detector: recover tool calls dropped by common model-outpu… sgl-project/sglang#34237

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fatday mentioned this pull request Aug 10, 2026

[Bugfix] Fix extreme case in pythonic parser argument json safety #51649

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zyp2014 pushed a commit to zyp2014/vllm that referenced this pull request Aug 21, 2026

[Bugfix] Fix lfm2 tool parser dropping calls with brackets or newline… (

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vllm-project#48171) Signed-off-by: Zetian Li <804561096@qq.com> Co-authored-by: Claude (Anthropic) <noreply@anthropic.com>

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[Bugfix] Fix lfm2 tool parser dropping calls with brackets or newline… - #48171

[Bugfix] Fix lfm2 tool parser dropping calls with brackets or newline…#48171
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[Bugfix] Fix lfm2 tool parser dropping or corrupting recoverable tool calls

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