Check for invalid UTF-8 encoded strings in cutsets

[dsnet]

The (strings|bytes).(IndexAny|LastIndexAny|ContainsAny|Trim|TrimLeft|TrimRight) functions take an argument for a set of UTF-8 encoded characters to match on. In production code, I have seen incorrect uses of these functions where the user treats chars as simply a list of bytes, rather UTF-8 encoded characters.

Most likely, any invalid chars input is due to user error. The following is probably not what a user expects:

fmt.Printf("%q\n", strings.Trim("\x80test\xff", "\xff"))

This currently prints test, while the user expectation is probably \x80test.

[dominikh]

@dsnet Is golint the right place for this check? AFAIK, golint is about style, not correctness. I'm currently trying to decide between sending a PR to golint and adding the check to my own staticcheck.

[dsnet]

I'm actually not sure. You are right that this is an issue about correctness, so it doesn't quite fit as a lint check either. According to golang/go#17780, the criterion for a vet check is: correctness, frequency, and precision.

When I looked over a large number of Go code inside Google, this mishap only occurred a few dozen times, so it probably doesn't hit the frequency requirements. If you want to add it to staticcheck, that would sound great.

[dominikh]

I've added the check to staticcheck. Running it against my corpus also yielded a very low number of results, so most likely not suitable for vet.

[dsnet]

I'm going to close this issue since the feature request fits neither vet nor lint. Thanks @dominikh for adding it to staticcheck.