json: refine whitespace rules to avoid runaways

[ochafik]

Quick follow up to #7841 (@HanClinto I took the bait of your "good start" 🤪)

Defining whitespace as ws ::= | " " | "\n" [ \t]{0,20} allows compact inline {"a": 1}, spacy inline { "a" : 1 } and indented JSON, but disallows multiple empty lines, multiple spaces not in an indenting context, etc.

For instance, this removes the trailing spaces generated by the following call:

./main --log-disable --seed 1133 \
  --grammar-file grammars/json.gbnf \
  -mu https://huggingface.co/bartowski/Meta-Llama-3-8B-Instruct-GGUF/resolve/main/Meta-Llama-3-8B-Instruct-Q8_0.gguf \
  -p "Tell me a love story with a JSON structure:
"

Show output from master

{
  "characters": [
    {"name": "Alex", "age": 25, "occupation": "Software Engineer"},
    {"name": "Maya", "age": 28, "occupation": "Graphic Designer"}
  ],
  "story": {
    "beginning": "Alex and Maya met at a coffee shop in the heart of the city.",
    "middle": "They bonded over their shared love of art and technology, and soon became inseparable.",
    "end": "After a year of dating, Alex proposed to Maya with a custom-made ring and a romantic sunset view."
  }
}





  





  

Seems to perform similarly to master with the couple of attempts I've done.

Show benchmark commands

hyperfine \
  --warmup 1 --runs 5 \
  -L branch master,json-ws \
  --prepare 'git checkout {branch} && make clean && make -j LLAMA_CURL=1 main' \
  'branch={branch} \
    ./main --log-disable --seed 1133 \
      --grammar-file grammars/json.gbnf \
      -mu https://huggingface.co/bartowski/Meta-Llama-3-8B-Instruct-GGUF/resolve/main/Meta-Llama-3-8B-Instruct-Q8_0.gguf \
      -p "Tell me a love story with a JSON structure:
      "'

Note: also tested ws ::= | " " | "\n" (" "{0,10} | "\t"{0,10}) but it's slower, probably because of the extra stack / alternatives overhead.

[HanClinto]

Looks good to me! 👍