I'm trying to strip away some text from part of a text. Trying to use something like sub("!.*"; "") doesn't work, as it is giving me a Segmentation fault when text is too long. So I tried to go this route:

$ jq '.msg | .[0:index("!")]'

which works fine with input like:
{"msg": "hello world!"}
but fails when text contains wide characters:
{"msg": "здравствуй мир!"}

$ echo '{"msg": "здравствуй мир!"}' | jq '.msg | index("!")'
27

$ echo '{"msg": "hello world!"}' | jq '.msg | index("!")'
11

$ jq --version
jq-1.5
$ uname -a
Darwin atschabu-C02SF0UTG8WM 15.6.0 Darwin Kernel Version 15.6.0: Tue Apr 11 16:00:51 PDT 2017; root:xnu-3248.60.11.5.3~1/RELEASE_X86_64 x86_64