Bug in the treatment of the anyOf keyword in JSON Schema

[RobinPicard]

Describe the issue as clearly as possible:

I ran into this issue while working on #495. It seems to be caused by the fact that the subregex generated for the anyOf keyword includes all permutations of the patterns of the types in question concatenated. I don't understand why we need to do such permutations. I have the impression that a simple "or" between the patterns associated to each type would work

Steps/code to reproduce the bug:

import json
import jsonschema
import re
from outlines.fsm.json_schema import build_regex_from_object

schema = {
    "properties": {
        "foo": {"anyOf": [{"type": "null"}, {"type": "boolean"}]},
    },
    "required": ["foo"],
    "type": "object",
}

regex = build_regex_from_object(json.dumps(schema))
print(regex)

wrong_response = '{ "foo" : nulltrue }'

if re.fullmatch(regex, wrong_response):
    print("match")

try:
    jsonschema.validate(instance=wrong_response, schema=schema)
except jsonschema.exceptions.ValidationError as err:
    print("no match")
    
# \{[\n ]*"foo"[\n ]*:[\n ]*((null)|((true|false))|(null(true|false))|((true|false)null))[\n ]*\}
# match
# no match

Expected result:

The wrong_response should not match with the regex

Error message:

No response

Outlines/Python version information:

Outlines: current main branch
Python: 3.9.6

Context for the issue:

No response