func Unquote()

in build/quote.go [86:196]
94 lines of code
29 McCabe index (conditional complexity)

func Unquote(quoted string) (s string, triple bool, err error) {
	// Check for raw prefix: means don't interpret the inner \.
	raw := false
	if strings.HasPrefix(quoted, "r") {
		raw = true
		quoted = quoted[1:]
	}

	if len(quoted) < 2 {
		err = fmt.Errorf("string literal too short")
		return
	}

	if quoted[0] != '"' && quoted[0] != '\'' || quoted[0] != quoted[len(quoted)-1] {
		err = fmt.Errorf("string literal has invalid quotes")
	}

	// Check for triple quoted string.
	quote := quoted[0]
	if len(quoted) >= 6 && quoted[1] == quote && quoted[2] == quote && quoted[:3] == quoted[len(quoted)-3:] {
		triple = true
		quoted = quoted[3 : len(quoted)-3]
	} else {
		quoted = quoted[1 : len(quoted)-1]
	}

	// Now quoted is the quoted data, but no quotes.
	// If we're in raw mode or there are no escapes, we're done.
	if raw || !strings.Contains(quoted, `\`) {
		s = quoted
		return
	}

	// Otherwise process quoted string.
	// Each iteration processes one escape sequence along with the
	// plain text leading up to it.
	var buf bytes.Buffer
	for {
		// Remove prefix before escape sequence.
		i := strings.Index(quoted, `\`)
		if i < 0 {
			i = len(quoted)
		}
		buf.WriteString(quoted[:i])
		quoted = quoted[i:]

		if len(quoted) == 0 {
			break
		}

		// Process escape sequence.
		if len(quoted) == 1 {
			err = fmt.Errorf(`truncated escape sequence \`)
			return
		}

		switch quoted[1] {
		default:
			// In Python, if \z (for some byte z) is not a known escape sequence
			// then it appears as literal text in the string.
			buf.WriteString(quoted[:2])
			quoted = quoted[2:]

		case '\n':
			// Ignore the escape and the line break.
			quoted = quoted[2:]

		case 'a', 'b', 'f', 'n', 'r', 't', 'v', '\\', '\'', '"':
			// One-char escape
			buf.WriteByte(unesc[quoted[1]])
			quoted = quoted[2:]

		case '0', '1', '2', '3', '4', '5', '6', '7':
			// Octal escape, up to 3 digits.
			n := int(quoted[1] - '0')
			quoted = quoted[2:]
			for i := 1; i < 3; i++ {
				if len(quoted) == 0 || quoted[0] < '0' || '7' < quoted[0] {
					break
				}
				n = n*8 + int(quoted[0]-'0')
				quoted = quoted[1:]
			}
			if n >= 256 {
				// NOTE: Python silently discards the high bit,
				// so that '\541' == '\141' == 'a'.
				// Let's see if we can avoid doing that in BUILD files.
				err = fmt.Errorf(`invalid escape sequence \%03o`, n)
				return
			}
			buf.WriteByte(byte(n))

		case 'x':
			// Hexadecimal escape, exactly 2 digits.
			if len(quoted) < 4 {
				err = fmt.Errorf(`truncated escape sequence %s`, quoted)
				return
			}
			n, err1 := strconv.ParseInt(quoted[2:4], 16, 0)
			if err1 != nil {
				err = fmt.Errorf(`invalid escape sequence %s`, quoted[:4])
				return
			}
			buf.WriteByte(byte(n))
			quoted = quoted[4:]
		}
	}

	s = buf.String()
	return
}