Lines not flushed correctly in presence of emoji

[y0ast]

• I have read through the manual page (man fzf)
• I have the latest version of fzf
• I have searched through the existing issues

Relevant:
#1526
#2163

But different enough for its own issue.

Info

• OS
  • Linux
  • Mac OS X
  • Windows
  • Etc.
• Shell
  • bash
  • zsh
  • fish

Problem / Steps to reproduce

curl https://raw.githubusercontent.com/LukeSmithxyz/voidrice/master/.local/share/larbs/emoji | fzf

Search for something, then remove a character and see spurious ; and other characters appear on lines. ctrl+L fixes it.

core problem is this:

import (
	"fmt"

	"github.com/mattn/go-runewidth"
)

func main() {
	fmt.Println(runewidth.StringWidth("☺️"))
	fmt.Println(runewidth.RuneWidth('☺')) // created from above but deleting the modifier
	fmt.Println(runewidth.RuneWidth('️')) // created from first line, but backspacing the emoji char leaving the modifier
}

$ go run main.go
1
1
1

Fzf computes width of line using runewidth.Runewidth instead of runewidth.StringWidth. The second takes into account zero width emoji modifiers:

RuneWidth of just emoji = 1, RuneWidth of the modier= 1, so fzf thinks length is 2
However StringWidth of emoji+modifier = 1 (which is correct)

When computing number of spaces to pad with, fzf misses 1 (or more) and random characters appear.

[junegunn]

Thanks for the repro and the suggested fix. I'll look into it when I get some time.

[y0ast]

Fix works! Thanks a lot :)