reflect: add sipmlified strconv.Quote() implementation for struct tags

src/reflect/strconv.go

@@ -30,6 +30,10 @@ func unhex(b byte) (v rune, ok bool) {
 	return
 }
 
+const (
+	lowerhex = "0123456789abcef"
+)
+
 // unquoteChar decodes the first character or byte in the escaped string
 // or character literal represented by the string s.
 // It returns four values:
@@ -231,6 +235,101 @@ func unquote(s string) (string, error) {
 	return string(buf), nil
 }
 
+func quote(s string) string {
+	buf := make([]byte, 0, 3*len(s)/2)
+	const quote = '"'
+
+	buf = append(buf, quote)
+	for width := 0; len(s) > 0; s = s[width:] {
+		r := rune(s[0])
+		width = 1
+		if r >= utf8.RuneSelf {
+			r, width = utf8.DecodeRuneInString(s)
+		}
+		if width == 1 && r == utf8.RuneError {
+			buf = append(buf, `\x`...)
+			buf = append(buf, lowerhex[s[0]>>4])
+			buf = append(buf, lowerhex[s[0]&0xF])
+			continue
+		}
+		buf = appendEscapedRune(buf, r)
+	}
+	buf = append(buf, quote)
+	return string(buf)
+}
+
+func appendEscapedRune(buf []byte, r rune) []byte {
+
+	const quote = '"'
+
+	var runeTmp [utf8.UTFMax]byte
+	if r == rune(quote) || r == '\\' { // always backslashed
+		buf = append(buf, '\\')
+		buf = append(buf, byte(r))
+		return buf
+	}
+	if isPrint(r) {
+		n := utf8.EncodeRune(runeTmp[:], r)
+		buf = append(buf, runeTmp[:n]...)
+		return buf
+	}
+	switch r {
+	case '\a':
+		buf = append(buf, `\a`...)
+	case '\b':
+		buf = append(buf, `\b`...)
+	case '\f':
+		buf = append(buf, `\f`...)
+	case '\n':
+		buf = append(buf, `\n`...)
+	case '\r':
+		buf = append(buf, `\r`...)
+	case '\t':
+		buf = append(buf, `\t`...)
+	case '\v':
+		buf = append(buf, `\v`...)
+	default:
+		switch {
+		case r < ' ' || r == 0x7f:
+			buf = append(buf, `\x`...)
+			buf = append(buf, lowerhex[byte(r)>>4])
+			buf = append(buf, lowerhex[byte(r)&0xF])
+		case !utf8.ValidRune(r):
+			r = 0xFFFD
+			fallthrough
+		case r < 0x10000:
+			buf = append(buf, `\u`...)
+			for s := 12; s >= 0; s -= 4 {
+				buf = append(buf, lowerhex[r>>uint(s)&0xF])
+			}
+		default:
+			buf = append(buf, `\U`...)
+			for s := 28; s >= 0; s -= 4 {
+				buf = append(buf, lowerhex[r>>uint(s)&0xF])
+			}
+		}
+	}
+	return buf
+}
+
+// This is only used for struct tags.  Assume
+func isPrint(r rune) bool {
+	if r <= 0xFF {
+		if 0x20 <= r && r <= 0x7E {
+			// All the ASCII is printable from space through DEL-1.
+			return true
+		}
+		if 0xA1 <= r && r <= 0xFF {
+			// Similarly for ¡ through ÿ...
+			return r != 0xAD // ...except for the bizarre soft hyphen.
+		}
+		return false
+	}
+
+	// TinyGo: Skip all other unicode processing
+	return false
+}
+
 // contains reports whether the string contains the byte c.
 func contains(s string, c byte) bool {
 	return indexByteString(s, c) != -1