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Port the Python `pythonic` / `llama4_pythonic` tool parsers to the Rust frontend so Llama 3.2 / Llama 4 style tool calls (a Python list of keyword-argument calls) can be served through it. Arguments are converted to JSON incrementally while streaming, matching the other Rust parsers, and the `llama4_pythonic` variant additionally drops the `<|python_start|>` / `<|python_end|>` markers. Part of vllm-project#44280 Signed-off-by: RickyYii <237135932+RickyYii@users.noreply.github.com>
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Records the duplicate-work findings for vllm-project#55848 and vllm-project#55850, the verified divergences between the Rust pythonic parser in vllm-project#55849 and vLLM's Python PythonicToolParser, the clean results (Hermes scanner fuzzing, chunking equivalence and streaming prefix stability), and ready-to-paste comment text for each PR. Signed-off-by: RickyYii <237135932+RickyYii@users.noreply.github.com>
…pythonic-tool-parser Signed-off-by: RickyYii <237135932+RickyYii@users.noreply.github.com> # Conflicts: # rust/src/chat/src/lib.rs # rust/src/chat/src/parser/tool/mod.rs
Differential testing against vLLM's own `PythonicToolParser` turned up
argument values that the two parsers disagree on. This closes the gaps:
- Integers are carried through as text instead of `serde_json::Value`.
`serde_json::Number` stops at `u64`, so anything wider was rounded into
an `f64` and the tool was called with a different amount than the model
wrote (`wei=123456789012345678901234567890` arrived as `1.2345e+29`).
Values are now assembled as JSON text throughout, which also drops the
`serde_json::to_string` step when an argument is emitted.
- Tuples parse as JSON arrays, as in the Python parser. Parentheses
without a trailing comma group a value, so `(1)` is `1` and `(1,)` is
`[1]`, matching Python.
- Binary, octal and hexadecimal integers and `_` digit separators are
accepted; the Python parser resolves them through `ast`.
- Whitespace is allowed between a function name and its `(`.
- `\N{NAME}` escapes are rejected instead of being passed through
verbatim. Decoding them needs a Unicode name table, and keeping the
escape as literal text handed the tool a different string than the
model wrote; failing sends the output to content instead.
- An invalid escape after already-decoded text no longer discards that
text. It was committed when a chunk boundary happened to fall before
the escape and dropped otherwise, so the same output parsed differently
depending on chunking.
Verified against the Python parser over 21 literal cases that previously
disagreed, and over 133 inputs x 200 random chunk splits each with no
chunking disagreements and no streaming prefix violations.
Signed-off-by: RickyYii <237135932+RickyYii@users.noreply.github.com>
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Purpose
Part of the Rust frontend parser-parity work tracked in #44280.
The Python frontend ships
pythonicandllama4_pythonictool parsers for models whose tool calls are a Python list of keyword-argument calls (Llama 3.2, Llama 4, ToolACE, ...), but the Rust frontend had no parser for that format:--tool-call-parser pythonic/llama4_pythonicwere not registered andllama-4could only be served through the JSON parser. This PR ports the format to the Rust frontend as a streaming parser:rust/src/parser/src/tool/pythonic/mod.rs:PythonicToolParser, a winnow/Partialbuffered-event parser in the same shape asLlama3JsonToolParser(explicit mode enum,parse_buffered_eventloop). The list must be the whole output; leading text permanently switches the parser to passthrough, exactly like the JSON parsers. Text that opens with[but is not a call list ([1, 2, 3],[],[not a call) is aParsingFailederror; because the opening[is only consumed together with the firstname(,reset()still returns the whole original text and the chat layer re-emits it as content, which reproduces the Python parser's "does not match the pattern, treat as text" behaviour. Trailing non-whitespace after]and an incomplete call atfinish()are errors, following the same convention asLlama3JsonToolParser.rust/src/parser/src/tool/pythonic/value.rs: Python literal parsers producingserde_json::Value(single/double-quoted strings with full Python escape decoding incl.\xhh, octal,\uXXXXwith surrogate pairing,\UXXXXXXXX, line continuation; ints, floats and signed numbers;True/False/Noneplus JSON-styletrue/false/null; nested lists and dicts with string keys, bounded by the existingParserRecursionGuard), and an incremental Python-string decoder used for streaming. Tuples, sets, f-strings, non-string dict keys and\N{...}escapes are rejected and left asTODOs in the code.rust/src/parser/src/tool/pythonic/llama4.rs:Llama4PythonicToolParser, a thin wrapper over the same core that also strips the<|python_start|>/<|python_end|>markers Llama 4 sometimes emits.name(, then{, then one"key":<json>fragment per completed argument (with,separators) and}at). String arguments are streamed as the Python literal arrives (opening quote, decoded runs, closing quote), so long string arguments such as file contents do not stall the stream; non-string values (numbers, keywords, nested lists/dicts) are emitted once complete. Arguments are compactserde_jsontext, matching the other Rust parsers that synthesize JSON (qwen_coder,glm_xml).pythonicandllama4_pythonicinrust/src/chat/src/parser/tool/mod.rs. No model-name routing changes:llama-4still resolves tollama4_json, and the pythonic parsers are selected explicitly with--tool-call-parser, the same as in Python.structural_tag_builder()staysNone(xgrammar has no structural tag for this format; the Python parser also hasstructural_tag_model = None).rust/src/parser/benches/pythonic.rs: native-vs-external comparison bench in the same shape as the existing per-parser benches.Duplicate check: no open PR adds a pythonic parser to the Rust frontend (
is:pr pythonic in:titleonly lists Python-side fixes); the open[Rust Frontend]parser PRs cover ERNIE 4.5 (#52841), Hunyuan A13B (#52133) and MiMo (#54393).Test Plan
Unit tests live next to the code (
expect-testsnapshots,rust/AGENTS.mdconventions): simple / parallel / parameterless calls, empty dict and list arguments, nested containers, escaped strings (theESCAPED_STRING_FUNCTION_OUTPUTcase from the Python tests plus\n/\t/unicode/octal/hex escapes),True/False/Noneand JSON literals, signed numbers, whitespace and newlines between calls and arguments, plain-text passthrough, non-call lists and malformed input (asserting the original text is handed back), the Llama 4 markers split across chunk boundaries,finish()on incomplete calls and trailing text, and a 4096-character string argument that must be committed before the call closes. Every parse test runs through aparse_chunkingshelper that asserts the coalesced output is byte-identical for the whole text, 3-character chunks and 1-character chunks. Registry tests inrust/src/chat/src/parser/tool/tests.rscover creation by name and thatllama-4model routing is unchanged.Test Result
cargo fmt --all -- --check: clean.cargo clippy --workspace --all-targets --all-features --locked -- -D warnings: clean.cargo test -p vllm-parser --all-features --locked: 467 passed, 0 failed (26 new pythonic tests).cargo test -p vllm-chat --all-features --locked --lib: 293 passed, 0 failed.cargo test --workspace --all-features --locked --lib --no-fail-fast: everything passes except the pre-existing tests that downloadQwen/Qwen3-0.6Bfrom the Hugging Face Hub (vllm-textlower_text_request_uses_real_qwen_generation_defaultsand thevllm-chatroundtripintegration tests), which cannot run in my sandbox and are unrelated to this change.cargo bench -p vllm-parser --features test-util --bench pythonic -- --test: all groups succeed.pre-commit run --files <changed files>: all applicable hooks pass (SPDX headers and the rust fmt hook included).AI assistance was used while developing this change (drafting the parser and tests); I reviewed every line and ran the commands above myself.