regexp: LiteralPrefix lies about completeness

[dvyukov]

The following program fails with the panic:

package main

import "regexp"

func main() {
    re := regexp.MustCompile("^")
    prefix, complete := re.LiteralPrefix()
    if !complete && re.MatchString(prefix) {
        panic("bad")
    }
}

If complete is false, Match must fail.

go version devel +b0532a9 Mon Jun 8 05:13:15 2015 +0000 linux/amd64

[cespare]

If complete is false, Match must fail.

Why? A match doesn't have to match the entire input.

http://play.golang.org/p/E4iOdS7Av0

[dvyukov]

It's the other way around here. In your example, there is leftover in the string. In my example, there is leftover in the regexp (according to LiteralPrefix).

[rsc]

If complete is false, Match must fail.

Not true. If complete is false it means that there is something to the regexp beyond what has been returned in 'prefix'.