[Rust Frontend] Add Olmo3 tool parser by 982945902 · Pull Request #52579 · vllm-project/vllm

982945902 · 2026-08-17T05:48:15Z

Purpose

Add the Olmo3 tool parser to the experimental Rust frontend.

Parses <function_calls>...</function_calls> blocks containing newline-separated Python-style calls.
Uses a bounded parser for the supported Python-literal subset instead of directly depending on the unmaintained rustpython-parser crate.
Supports parallel calls, nested dict/list/tuple literals, Python and JSON boolean/null literals, parameterless calls, and arbitrary stream chunk boundaries.
Preserves visible text before and after tool calls in event order.
Falls back to ordinary text for incomplete or unsupported tool-call expressions instead of panicking.
Registers the olmo3 parser and automatic olmo-3 / olmo3 model matchers.
Adds a real allenai/Olmo-3-7B-Instruct tokenizer/template roundtrip fixture.

Tracks the Olmo3 tool-parser item in #44280.

Duplicate-work check

Before implementation and again before opening this PR, I checked:

comments on [Roadmap] Rust Frontend Feature Parity #44280;
open PRs referencing [Roadmap] Rust Frontend Feature Parity #44280;
open PR searches for olmo3 rust tool parser and related Rust frontend keywords.

I found no open PR implementing the Olmo3 Rust tool parser. #47345 is an Olmo3 reasoning-parser PR and does not overlap this change.

AI assistance

AI assistance was used to inspect the existing parser architecture, implement the Rust changes, and prepare tests. The human submitter is responsible for reviewing every changed line and defending the change end-to-end.

Test Plan

cargo test --manifest-path rust/Cargo.toml -p vllm-parser --lib
cargo test --manifest-path rust/Cargo.toml -p vllm-chat --lib
HF_HUB_OFFLINE=1 cargo test --manifest-path rust/Cargo.toml \
  -p vllm-chat --test roundtrip roundtrip_olmo3
cargo clippy --manifest-path rust/Cargo.toml \
  -p vllm-parser -p vllm-chat --all-targets -- -D warnings
pre-commit run --files \
  rust/Cargo.lock rust/Cargo.toml rust/src/chat/src/lib.rs \
  rust/src/chat/src/parser/tool/mod.rs rust/src/chat/src/parser/tool/tests.rs \
  rust/src/chat/tests/roundtrip.rs rust/src/parser/Cargo.toml \
  rust/src/parser/src/tool/mod.rs rust/src/parser/src/tool/olmo3.rs

The roundtrip test uses cached tokenizer/template files from the official allenai/Olmo-3-7B-Instruct repository; no model weights or GPU are required.

A model-quality evaluation is not applicable because this change does not alter model execution or generated outputs. A full-model serving regression was performed to validate parser integration, as recorded below.

Test Result

vllm-parser: 441 passed.
vllm-chat library: 278 passed.
Olmo3 real model-family roundtrip: 1 passed.
Clippy with -D warnings: passed.
Changed-file pre-commit hooks: passed.

Full-model serving regression

Downloaded and served the complete allenai/Olmo-3-7B-Instruct checkpoint (13.59 GiB) on the CPU backend with the locally built PR Rust binary, --tool-call-parser olmo3, and the real model tokenizer/chat template.

/health and /v1/models: passed.
Plain chat: returned exactly hello.
Required single tool: returned one get_weather call with {"city":"Shanghai"} and finish_reason = "tool_calls".
Required parallel tools: returned ordered Shanghai and Beijing calls.
Text before tool call: preserved content = "I will check." before the parsed tool call.
Streaming parallel tools: six SSE chunks reconstructed into two complete ordered calls and ended with finish_reason = "tool_calls".

github-actions · 2026-08-17T05:48:25Z

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🚀

982945902 · 2026-08-17T05:48:29Z

This is my second Rust frontend contribution and the account currently has 0 merged PRs. The new-contributor pre-commit workflow requires a maintainer-applied verified, ready, or ready-run-all-tests label. Could a maintainer please review the submission metadata and add verified so CI can run? I will keep the PR in Draft until I have completed a human line-by-line review.

982945902 · 2026-08-17T07:03:03Z

Full allenai/Olmo-3-7B-Instruct CPU serving regression completed on August 17, 2026 and added to the PR description. The locally built PR Rust frontend passed health/models, plain chat, required single-tool, ordered parallel-tool, visible-text-before-tool, and streaming parallel-tool reconstruction cases. The key mixed-output case returned content: "I will check." followed by a parsed get_weather({"city":"Shanghai"}) tool call.

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BugenZhao · 2026-08-17T21:37:03Z

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chatgpt-codex-connector · 2026-08-17T21:41:21Z

+                    let Some(marker_start) = self.buffer.find(END) else {
+                        return Ok(());
+                    };


Stream tool calls before the closing wrapper

For every streaming Olmo response, this branch returns without emitting any tool-call event until </function_calls> arrives, so a long-running call buffers its entire name and arguments and produces no SSE tool delta until generation has effectively finished. This defeats incremental streaming and can create an unbounded latency and memory spike for large arguments; completed newline-delimited calls, or at least safe argument prefixes, should be emitted as chunks arrive.

Useful? React with 👍 / 👎.

Addressed in f89fdc9685. The streaming state machine now detects a syntactically complete Python call and emits its ToolCall event as soon as the closing parenthesis arrives, before </function_calls>. Parallel calls are emitted independently as each completes. Added regressions for emission before the wrapper end and per-call parallel streaming.

chatgpt-codex-connector · 2026-08-17T21:41:21Z

+    text.parse::<f64>()
+        .ok()
+        .and_then(Number::from_f64)
+        .map(Value::Number)


Preserve arbitrary-precision integer arguments

When an Olmo call contains an integer outside the i64/u64 range, this fallback converts the exact RustPython bigint to f64, silently rounding it before serialization. For example, lookup(id=18446744073709551617) is returned with a different numeric value, which can address the wrong record or corrupt an identifier; such integers need exact textual/JSON preservation or should be rejected instead of approximated.

Useful? React with 👍 / 👎.

Addressed in f89fdc9685. Integers outside the exact serde_json i64/u64 range are now rejected, causing the wrapper to fall back to assistant text instead of converting through f64 and silently rounding. Added a regression using 18446744073709551617.

chatgpt-codex-connector · 2026-08-17T21:41:21Z

+    let Expr::Name(function) = *call.func else {
+        return Err(parsing_failed!("unsupported Olmo3 function reference"));
+    };


Accept dotted Pythonic function names

When a declared tool uses a dotted name and the model emits a Pythonic call such as weather.get(city='Paris'), RustPython represents the target as Expr::Attribute, so this check rejects the entire wrapper and exposes it as plain assistant text. The existing Python Olmo path deliberately walks attribute chains in handle_single_tool, and the Rust request layer does not prohibit dotted tool names, so the Rust parser should preserve these callable names rather than accepting only Expr::Name.

Useful? React with 👍 / 👎.

Addressed in f89fdc9685. Callable extraction now walks RustPython Expr::Attribute chains down to Expr::Name and preserves names such as weather.client.get. Added a dotted-name regression.

982945902 · 2026-08-18T14:02:50Z

Rebased onto the latest main and addressed all three Codex review findings in f89fdc9685.

Validation after the rebase:

cargo test --manifest-path rust/Cargo.toml -p vllm-parser --lib — 425 passed
cargo test --manifest-path rust/Cargo.toml -p vllm-chat --lib — 268 passed
cargo test --manifest-path rust/Cargo.toml -p vllm-chat --test roundtrip olmo3 — passed
cargo clippy --manifest-path rust/Cargo.toml -p vllm-parser -p vllm-chat --all-targets -- -D warnings — passed
pre-commit hooks on all PR files — passed

@codex review

chatgpt-codex-connector · 2026-08-18T14:03:03Z

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982945902 · 2026-08-26T03:15:00Z

Rebased onto the latest main, resolved the roundtrip compile regression caused by the new ThinkingBehavior argument, and rechecked the three earlier automated review findings.

Validation on the current head:

cargo test --manifest-path rust/Cargo.toml -p vllm-parser --lib — 431 passed
cargo test --manifest-path rust/Cargo.toml -p vllm-chat --lib — 275 passed
cargo test --manifest-path rust/Cargo.toml -p vllm-chat --test roundtrip olmo3 — 1 passed
Clippy with -D warnings — passed
changed-file pre-commit hooks — passed

DCO now passes and the PR is mergeable. The remaining failed pre-run-check is the first-time-contributor gate; could a maintainer add verified or ready so CI can run?

mergify · 2026-08-29T08:38:55Z

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @982945902.

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

982945902 · 2026-08-31T05:53:48Z

Rebased onto current main (687db59744) and resolved the parser-name/Cargo manifest conflicts while preserving the current serde rc feature.

Validation on the rebased head:

vllm-parser: 439 passed
vllm-chat: 278 passed
Olmo3 tokenizer/template roundtrip: 1 passed
Clippy with -D warnings: passed
changed-file pre-commit hooks: passed

depthfirst-app · 2026-08-31T05:58:49Z

@@ -90,6 +90,7 @@ rlimit = "0.11.0"
 rmp-serde = "1.3.1"
 rmpv = { version = "1.3.1", features = ["with-serde"] }
 rustc-hash = "1.1.0"
+rustpython-parser = "0.4.0"


⚪ Severity: LOW

The rustpython-parser crate is unmaintained — the RustPython project has officially moved to Ruff's parser and plans to archive this repository (source). It also pulls in multiple unmaintained transitive dependencies (paste, several unic-* crates) flagged by RUSTSEC advisories. Using it to parse adversarial model output means future parser bugs will never be patched.
Helpful? Add 👍 / 👎

💡 Fix Suggestion

Suggestion: Replace the unmaintained rustpython-parser crate with a maintained Python expression parser. The recommended migration path is to use the ruff_python_parser crate from the Ruff project, which is actively maintained and is the official successor to the RustPython parser. This would involve:

Replace rustpython-parser = "0.4.0" in rust/Cargo.toml with the appropriate ruff_python_parser and ruff_python_ast crates.

Update all imports and API calls in rust/src/parser/src/tool/olmo3.rs (lines 4-8, 69, 279, 288) to use Ruff's parser API (e.g., ruff_python_parser::parse_expression() and ruff_python_ast types).

Adapt the AST traversal logic (the parse_call, expr_to_value, and constant-handling code) to work with Ruff's AST representation, which differs from RustPython's (e.g., Ruff uses separate Expr::NumberLiteral, Expr::StringLiteral, etc. instead of a single Expr::Constant).

Alternatively, if the subset of Python expressions being parsed is small enough (function calls with literal arguments), consider writing a hand-rolled parser that avoids the external dependency entirely, similar to how other tool parsers in the codebase work.

Addressed in c4775a3bdf. I removed the direct rustpython-parser dependency and replaced the general Python AST parser with a bounded parser for the exact Olmo3 subset: dotted callable names, keyword arguments, strings, JSON/Python booleans and nulls, numbers, lists, tuples, and string-keyed dictionaries. Arbitrary expressions are rejected without evaluation, and nesting is capped at 64 levels.

Validation:

vllm-parser: 441 passed

vllm-chat: 278 passed

Olmo3 tokenizer/template roundtrip: 1 passed

Clippy with -D warnings: passed

changed-file pre-commit hooks: passed

rustpython-parser is absent from the production vllm-parser dependency tree (it remains only through the pre-existing tool-parser dev-dependency).

Stream completed calls before the closing wrapper, preserve dotted callable names, and reject out-of-range integers instead of rounding them. Co-authored-by: OpenAI Codex <codex@openai.com> Signed-off-by: lishuo121 <lishuo121@jd.com> Signed-off-by: chuanzhisongshu <49055103+982945902@users.noreply.github.com>

mergify · 2026-09-10T20:30:16Z

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @982945902.

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

mergify Bot added the rust label Aug 17, 2026

982945902 mentioned this pull request Aug 17, 2026

[Roadmap] Rust Frontend Feature Parity #44280

Open

982945902 marked this pull request as ready for review August 17, 2026 13:09

982945902 requested review from BugenZhao and njhill as code owners August 17, 2026 13:09

claude Bot reviewed Aug 17, 2026

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chatgpt-codex-connector Bot reviewed Aug 17, 2026

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982945902 force-pushed the codex/20260817-olmo3-tool-parser branch from 9b6c492 to f89fdc9 Compare August 18, 2026 14:01

982945902 mentioned this pull request Aug 19, 2026

[Rust Frontend] Add LFM2 tool parser #52900

Open

hmellor mentioned this pull request Aug 24, 2026

[Model] Migrate FlexOlmo, Olmo3 and Hunyuan V1/VL to the Transformers modeling backend #53615

Merged

982945902 force-pushed the codex/20260817-olmo3-tool-parser branch from f89fdc9 to 0299969 Compare August 26, 2026 03:10

mergify Bot added the needs-rebase label Aug 29, 2026

982945902 force-pushed the codex/20260817-olmo3-tool-parser branch from 0299969 to a648f47 Compare August 31, 2026 05:51

mergify Bot removed the needs-rebase label Aug 31, 2026

depthfirst-app Bot reviewed Aug 31, 2026

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982945902 force-pushed the codex/20260817-olmo3-tool-parser branch from a648f47 to c4775a3 Compare September 8, 2026 10:08

mergify Bot added the needs-rebase label Sep 10, 2026

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Purpose

Duplicate-work check

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Test Plan

Test Result

Full-model serving regression

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