func singleLiteralToCharClass(rx *syntax.Regexp) {
if rx.Op == syntax.OpLiteral && len(rx.Rune) == 1 {
char := rx.Rune[0]
if rx.Flags&syntax.FoldCase != 0 && unicode.ToLower(char) != unicode.ToUpper(char) {
l, h := unicode.ToLower(char), unicode.ToUpper(char)
rx.Rune = []rune{h, h, l, l}
rx.Rune0 = [...]rune{h, h}
} else {
rx.Rune = []rune{char, char}
rx.Rune0 = [...]rune{char, char}
}
rx.Op = syntax.OpCharClass
}
}
