github.com/ladydascalie/elvish@v0.0.0-20170703214355-2964dd3ece7f/parse/quote.go

package parse

import (
	"bytes"
	"unicode"
)

var QuotingStyles = []struct {
	Type   PrimaryType
	Quoter string
}{
	{SingleQuoted, "'"},
	{DoubleQuoted, "\""},
}

// Quote returns a representation of s in elvish syntax. Bareword is tried
// first, then single quoted string and finally double quoted string.
func Quote(s string) string {
	s, _ = QuoteAs(s, Bareword)
	return s
}

// QuoteAs returns a representation of s in elvish syntax, using the syntax
// specified by q, which must be one of Bareword, SingleQuoted, or
// DoubleQuoted. It returns the quoted string and the actual quoting.
func QuoteAs(s string, q PrimaryType) (string, PrimaryType) {
	if q == DoubleQuoted {
		// Everything can be quoted using double quotes, return directly.
		return quoteDouble(s), DoubleQuoted
	}
	if s == "" {
		return "''", SingleQuoted
	}

	// Keep track of whether it is a valid bareword.
	bare := s[0] != '~'
	for _, r := range s {
		if !unicode.IsPrint(r) {
			// Contains unprintable character; force double quote.
			return quoteDouble(s), DoubleQuoted
		}
		if !allowedInBareword(r, false) {
			bare = false
		}
	}

	if q == Bareword && bare {
		return s, Bareword
	}
	return quoteSingle(s), SingleQuoted
}

func quoteSingle(s string) string {
	var buf bytes.Buffer
	buf.WriteByte('\'')
	for _, r := range s {
		buf.WriteRune(r)
		if r == '\'' {
			buf.WriteByte('\'')
		}
	}
	buf.WriteByte('\'')
	return buf.String()
}

func rtohex(r rune, w int) []byte {
	bytes := make([]byte, w)
	for i := w - 1; i >= 0; i-- {
		d := byte(r % 16)
		r /= 16
		if d <= 9 {
			bytes[i] = '0' + d
		} else {
			bytes[i] = 'a' + d - 10
		}
	}
	return bytes
}

func quoteDouble(s string) string {
	var buf bytes.Buffer
	buf.WriteByte('"')
	for _, r := range s {
		if e, ok := doubleUnescape[r]; ok {
			// Takes care of " and \ as well.
			buf.WriteByte('\\')
			buf.WriteRune(e)
		} else if !unicode.IsPrint(r) {
			buf.WriteByte('\\')
			if r <= 0xff {
				buf.WriteByte('x')
				buf.Write(rtohex(r, 2))
			} else if r <= 0xffff {
				buf.WriteByte('u')
				buf.Write(rtohex(r, 4))
			} else {
				buf.WriteByte('U')
				buf.Write(rtohex(r, 8))
			}
		} else {
			buf.WriteRune(r)
		}
	}
	buf.WriteByte('"')
	return buf.String()
}