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I think this is because our text.DisplayWidth() helper only recognizes Unicode characters for written languages that take a double-width space

but does not recognize that all emoji (including ones that are a multibyte sequence) are always presented as a single-space character. We would need to teach the helper to recognize emoji characters.

This issue is a bit tricky, I did some digging. It is caused mostly by the East Asian Ambiguous characters and a few characters that are made up of multiple runes.

Example code (using the same DisplayWidth from the codebase):

package main

import (
    "fmt"
    "golang.org/x/text/width"
)

func DisplayWidth(s string) int {
	w := 0
	for _, r := range s {
		w += runeDisplayWidth(r)
	}
	return w
}

func runeDisplayWidth(r rune) int {
	switch width.LookupRune(r).Kind() {
        case width.EastAsianWide, width.EastAsianFullwidth, width.EastAsianAmbiguous:
            return 2
        default:
            return 1
	}
}

func main() {
    string1 := "♂️"
    string2 := "“"

    fmt.Printf("%2v (%v): %v\n", string1, []rune(string1), DisplayWidth(string1))
    fmt.Printf("%2v (%v): %v\n", string2, []rune(string2), DisplayWidth(string2))
}

Output:

♂️ ([9794 65039]): 4
 “ ([8220]): 2

While returning 1 for EastAsianAmbiguous case fixes a few cases (like string2 in the sample code) in the runeDisplayWidth function, it doesn't solve all the cases (like string1 which is made up of multiple runes)

I searched around on the web and there doesn't seem to be any fool proof solution for this.