[Refactor][Parser] Migrate chat completion auto-tool/reasoning/plain streaming to parse_delta#39446
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chaunceyjiang merged 2 commits intovllm-project:mainfrom Apr 14, 2026
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This pull request refactors the chat completion serving logic to use a unified Parser interface, simplifying the handling of streaming deltas for reasoning and tool calls. The changes include initializing a parser class via ParserManager and replacing manual delta extraction logic with parser.parse_delta. Feedback indicates a potential issue where reasoning data might be lost if a single streaming chunk contains both the end of a reasoning block and the start of a tool call, as the reasoning delta could be overwritten.
sfeng33
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…streaming to parse_delta (vllm-project#39446) Signed-off-by: sfeng33 <4florafeng@gmail.com>
avinashsingh77
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Apr 27, 2026
…streaming to parse_delta (vllm-project#39446) Signed-off-by: sfeng33 <4florafeng@gmail.com> Signed-off-by: Avinash Singh <avinashsingh.rcoem@gmail.com>
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Purpose
Migrate branches in chat_completion_stream_generator (auto tool + reasoning, auto tool only, reasoning only, plain content) with unified Parser.parse_delta() calls.
Test Plan
Verified for chat completion api, there is no behaviour change:
vllm serve Qwen/Qwen3-4B --reasoning-parser qwen3 --tool-call-parser hermes --enable-auto-tool-choicevllm serve Qwen/Qwen3-4B --reasoning-parser qwen3vllm serve Qwen/Qwen3-4B --tool-call-parser hermes --enable-auto-tool-choicevllm serve Qwen/Qwen3-4B