Adds support for quoted UTF8 label and metric names

lexer.go

@@ -399,6 +399,30 @@ func unescapeIdent(s string) string {
 	}
 }
 
+func hasEscapedChars(s string) bool {
+	i := 0
+	for i < len(s) {
+		r, size := utf8.DecodeRuneInString(s[i:])
+		if i == 0 && !isFirstIdentChar(r) || i > 0 && !isIdentChar(r) {
+			return true
+		}
+		i += size
+	}
+	return false
+}
+func fEscapedCharsAppendQuotedIdent(dst []byte, s string) []byte {
+	if hasEscapedChars(s) {
+		dst = utf8.AppendRune(dst, '"')
+		for i := 0; i < len(s); {
+			r, size := utf8.DecodeRuneInString(s[i:])
+			dst = utf8.AppendRune(dst, r)
+			i += size
+		}
+		dst = utf8.AppendRune(dst, '"')
+		return dst
+	}
+	return appendEscapedIdent(dst, s)
+}
 func appendEscapedIdent(dst []byte, s string) []byte {
 	i := 0
 	for i < len(s) {

parser.go

@@ -1462,7 +1462,7 @@ type labelFilterExpr struct {
 }
 
 func (lfe *labelFilterExpr) AppendString(dst []byte) []byte {
-	dst = appendEscapedIdent(dst, lfe.Label)
+	dst = ifEscapedCharsAppendQuotedIdent(dst, lfe.Label)
 	if lfe.Value == nil {
 		return dst
 	}
@@ -2267,15 +2267,28 @@ type MetricExpr struct {
 func appendLabelFilterss(dst []byte, lfss [][]*labelFilterExpr) []byte {
 	offset := 0
 	metricName := getMetricNameFromLabelFilterss(lfss)
+	metricNameHasEscapedChars := hasEscapedChars(metricName)
+
 	if metricName != "" {
 		offset = 1
-		dst = appendEscapedIdent(dst, metricName)
+		if !metricNameHasEscapedChars {
+			dst = appendEscapedIdent(dst, metricName)
+		} else {
+			dst = append(dst, '{')
+			dst = ifEscapedCharsAppendQuotedIdent(dst, metricName)
+		}
 	}
 	if isOnlyMetricNameInLabelFilterss(lfss) {
+		if metricNameHasEscapedChars {
+			dst = append(dst, '}')
+		}
 		return dst
 	}
-
-	dst = append(dst, '{')
+	if !metricNameHasEscapedChars {
+		dst = append(dst, '{')
+	} else {
+		dst = append(dst, ',', ' ')
+	}
 	for i, lfs := range lfss {
 		lfs = lfs[offset:]
 		if len(lfs) == 0 {
@@ -2335,7 +2348,11 @@ func mustGetMetricName(lfss []*labelFilterExpr) string {
 	}
 	lfs := lfss[0]
 	if lfs.Label != "__name__" || lfs.Value == nil || len(lfs.Value.tokens) != 1 {
-		return ""
+		if lfs.IsPossibleMetricName {
+			return lfs.Label
+		} else {
+			return ""
+		}
 	}
 	metricName, err := extractStringValue(lfs.Value.tokens[0])
 	if err != nil {

prettifier_test.go

@@ -101,7 +101,16 @@ func TestPrettifySuccess(t *testing.T) {
 
 	// Verify that short queries remain single-line
 	same(`foo`)
+	another(`{"foo"}`, "foo")
+	another(`{"3foo"}`, `{"3foo"}`)
+	another(`{"foo", bar="baz"}`, `foo{bar="baz"}`)
+	another(`{"foo", "bar"="baz"}`, `foo{bar="baz"}`)
 	same(`foo{bar="baz"}`)
+	another(`foo{"3bar"="baz"}`, `foo{"3bar"="baz"}`)
+	another(`foo{"bar3"="baz"}`, `foo{bar3="baz"}`)
+	same(`"metr\"ic"`)
+	same(`'metr"ic'`)
+	same(`{"3foo", bar="baz"}`)
 	same(`foo{bar="baz",x="y" or q="w",r="t"}`)
 	same(`foo{bar="baz"} + rate(x{y="x"}[5m] offset 1h)`)