How to check if a string contain 2 same char in a row?

I have a regex like this

REGEX_2_SAME_CHARACTER_IN_A_ROW = "^(?:(.)(?!\\))*$"

and check password with that regex if it contain 2 same character in a row

contain2SameCharacterInARow, err := regexp.MatchString(REGEX_2_SAME_CHARACTER_IN_A_ROW, password)

but I get this error

error match regex 2 same char in a row: error parsing regexp: invalid or unsupported Perl syntax: `(?!`

I have read other question that using regexp.MustCompile but I don't know how to handle or code it, is there anyone can help me with the solution?

Here you can check my full code for validate password
https://play.golang.com/p/5Fj4-UPvL8s

You don't need the anchor, the non-capturing group, nor the negative lookahead. Simply match and capture any character ((.)) followed by itself (\\1).

REGEX_2_SAME_CHARACTER_IN_A_ROW = "(.)\"

But this brings us to the next problem: Go regexes do not support back references, so you need to find a different solution. One would be looping the string yourself.

Here's a solution with a simple loop:

package main

import (
	"errors"
	"fmt"
	"strings"
)

func main() {
	fmt.Println(ValidatePassword("passsword01"))
}

func ContainsRepeatedChar(s string) bool {
	chars := strings.Split(s, "")
	char := chars[0]
	for i := 1; i < len(chars); i++ {
		if (chars[i] == char) {
			return true
		}
		char = chars[i]
	}
	return false
}

func ValidatePassword(password string) error {
	contain2SameCharacterInARow := ContainsRepeatedChar(password)
	if contain2SameCharacterInARow {
		fmt.Println("duplicated char")
		return errors.New("invalid password")
	}

	fmt.Println("all good")
	return nil
}