ozanh/ugo

//go:build !go1.20
// +build !go1.20

package compat

import (
    "fmt"
    "strconv"
    "unicode/utf8"
)

// FmtFormatString is a compatibility wrapper for fmt.FormatString, added in
// go1.20.
func FmtFormatString(state fmt.State, verb rune) string {
    var tmp [16]byte // Use a local buffer.
    b := append(tmp[:0], '%')
    for _, c := range " +-#0" {
        if state.Flag(int(c)) {
            b = append(b, byte(c))
        }
    }
    if w, ok := state.Width(); ok {
        b = strconv.AppendInt(b, int64(w), 10)
    }
    if p, ok := state.Precision(); ok {
        b = append(b, '.')
        b = strconv.AppendInt(b, int64(p), 10)
    }
    if verb < utf8.RuneSelf {
        b = append(b, byte(verb))
        return string(b)
    }
    var verbb [utf8.UTFMax]byte
    n := utf8.EncodeRune(verbb[:], verb)
    b = append(b, verbb[:n]...)
    return string(b)
}