Name and Version

The following legal grammar works correctly:

thinkblock ::= <think> !</think>* </think>
any ::= .
root ::= (thinkblock | any)*

This slightly altered version that is syntactically valid and equivalent breaks llama:

thinkblock ::= <think> !</think>* </think>
any ::= .*
root ::= (thinkblock | any)*

For example:

podman run -it -v /tmp:/grammar:ro -v /llama:/llama:ro --entrypoint /app/llama-completion ghcr.io/ggml-org/llama.cpp:full -m /llama/qwen3/Qwen3VL-8B-Instruct-Q4_K_M.gguf --grammar-file /grammar/grammar.gbnf -p 'yolo'

starts babbling in Chinese with the former but does not output anything with the latter.

This is particularly bad with llama's server, as using the latter grammar will break the server completely until it's restarted.

Operating systems

Linux

Which llama.cpp modules do you know to be affected?

libllama (core library), Other (Please specify in the next section)

Command line

podman run -it -v /tmp:/grammar:ro -v /llama:/llama:ro --entrypoint /app/llama-completion ghcr.io/ggml-org/llama.cpp:full -m /llama/qwen3/Qwen3VL-8B-Instruct-Q4_K_M.gguf --grammar-file /grammar/grammar.gbnf -p 'yolo'

Problem description & steps to reproduce

Breaks server until restart

First Bad Commit

No response

Relevant log output

No response