Match any string also containing escaped characters and newlines with Go

Any (format) strings in a file (C or C++ code), even containing escaped characters or newlines are needed to be found by a tool written in Go. Examples:

..."foo"...
...`foo:"foo"`...
..."foo
foo"...
..."foo\r\nfoo"...
...`foo"foo-

lish`

The C/C++ parsing is allowed to be done also in comments or deactivated code, so no need to exclude that parts.

I succeeded with

/(["'`])(?:(?=(\?))\2.)*?\1/gms

on https://regex101.com/r/FDhldb/1 searching for a solution.

Unfortunately this does not compile in Go:

const (
patFmtString = `(?Us)(["'])(?:(?=(\\?)).)*?`
)
var (
matchFmtString = regexp.MustCompile(patFmtString)
) 

Even the simplified pattern (?Us)(["'])(?:(\\?).)*?\1 delivers "error parsing regexp: invalid escape sequence: \1".

How do I correctly implement that in Go, hopefully running also fast?

You can use a reasonably simple Scanner to accomplish this instead of using PCRE:

import "bufio"

var stringLiterals bufio.SplitFunc = func(data []byte, atEOF bool) (advance int, token []byte, err error) {
	scanning := false
	var delim byte
	var i int
	var start, end int
	for i < len(data) {
		b := data[i]
		switch b {
		case '\\': // skip escape sequences
			i += 2
			continue
		case '"':
			fallthrough
		case '\'':
			fallthrough
		case '`':
			if scanning && delim == b {
				end = i + 1
				token = data[start:end]
				advance = end
				return
			} else if !scanning {
				scanning = true
				start = i
				delim = b
			}
		}
		i++
	}
	if atEOF {
		return len(data), nil, nil
	}
	return start, nil, nil
}

and use it like

func main() {
    input := /* some reader */
    scanner := bufio.NewScanner(input)
    scanner.Split(stringLiterals)
    for scanner.Scan() {
        stringLit := scanner.Text()
        // do something with `stringLit`
    }
}

For you examples, this returns exactly the matches that your regex does, though I'm not sure that actually corresponds to the way C++ string literals are defined in the grammar.

You can try it out on the playground.