Quote label name in matchers when needed

When the label name of a matcher contains non-standard characters, like
a dot, or starts with a digit, it should be quoted.

If it's not quoted, then `VectorSelector.String()` isn't a valid PromQL.

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

model/labels/matcher.go

@@ -78,8 +78,21 @@ func MustNewMatcher(mt MatchType, name, val string) *Matcher {
 }
 
 func (m *Matcher) String() string {
+	if !m.shouldQuoteName() {
 		return fmt.Sprintf("%s%s%q", m.Name, m.Type, m.Value)
 	}
+	return fmt.Sprintf("%q%s%q", m.Name, m.Type, m.Value)
+}
+
+func (m *Matcher) shouldQuoteName() bool {
+	for i, c := range m.Name {
+		if c == '_' || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (i > 0 && c >= '0' && c <= '9') {
+			continue
+		}
+		return true
+	}
+	return false
+}
 
 // Matches returns whether the matcher matches the given string value.
 func (m *Matcher) Matches(s string) bool {

model/labels/matcher_test.go

@@ -15,6 +15,7 @@ package labels
 
 import (
 	"fmt"
+	"math/rand"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -225,3 +226,128 @@ func BenchmarkNewMatcher(b *testing.B) {
 		}
 	})
 }
+
+func BenchmarkMatcher_String(b *testing.B) {
+	type benchCase struct {
+		name     string
+		matchers []*Matcher
+	}
+	cases := []benchCase{
+		{
+			name: "short name equal",
+			matchers: []*Matcher{
+				MustNewMatcher(MatchEqual, "foo", "bar"),
+				MustNewMatcher(MatchEqual, "bar", "baz"),
+				MustNewMatcher(MatchEqual, "abc", "def"),
+				MustNewMatcher(MatchEqual, "ghi", "klm"),
+				MustNewMatcher(MatchEqual, "nop", "qrs"),
+			},
+		},
+		{
+			name: "short quoted name not equal",
+			matchers: []*Matcher{
+				MustNewMatcher(MatchEqual, "f.o", "bar"),
+				MustNewMatcher(MatchEqual, "b.r", "baz"),
+				MustNewMatcher(MatchEqual, "a.c", "def"),
+				MustNewMatcher(MatchEqual, "g.i", "klm"),
+				MustNewMatcher(MatchEqual, "n.p", "qrs"),
+			},
+		},
+		{
+			name: "short quoted name with quotes not equal",
+			matchers: []*Matcher{
+				MustNewMatcher(MatchEqual, `"foo"`, "bar"),
+				MustNewMatcher(MatchEqual, `"foo"`, "baz"),
+				MustNewMatcher(MatchEqual, `"foo"`, "def"),
+				MustNewMatcher(MatchEqual, `"foo"`, "klm"),
+				MustNewMatcher(MatchEqual, `"foo"`, "qrs"),
+			},
+		},
+		{
+			name: "short name value with quotes equal",
+			matchers: []*Matcher{
+				MustNewMatcher(MatchEqual, "foo", `"bar"`),
+				MustNewMatcher(MatchEqual, "bar", `"baz"`),
+				MustNewMatcher(MatchEqual, "abc", `"def"`),
+				MustNewMatcher(MatchEqual, "ghi", `"klm"`),
+				MustNewMatcher(MatchEqual, "nop", `"qrs"`),
+			},
+		},
+		{
+			name: "short name and long value regexp",
+			matchers: []*Matcher{
+				MustNewMatcher(MatchRegexp, "foo", "five_six_seven_eight_nine_ten_one_two_three_four"),
+				MustNewMatcher(MatchRegexp, "bar", "one_two_three_four_five_six_seven_eight_nine_ten"),
+				MustNewMatcher(MatchRegexp, "abc", "two_three_four_five_six_seven_eight_nine_ten_one"),
+				MustNewMatcher(MatchRegexp, "ghi", "three_four_five_six_seven_eight_nine_ten_one_two"),
+				MustNewMatcher(MatchRegexp, "nop", "four_five_six_seven_eight_nine_ten_one_two_three"),
+			},
+		},
+		{
+			name: "short name and long value with quotes equal",
+			matchers: []*Matcher{
+				MustNewMatcher(MatchEqual, "foo", `five_six_seven_eight_nine_ten_"one"_two_three_four`),
+				MustNewMatcher(MatchEqual, "bar", `one_two_three_four_five_six_"seven"_eight_nine_ten`),
+				MustNewMatcher(MatchEqual, "abc", `two_three_four_five_six_seven_"eight"_nine_ten_one`),
+				MustNewMatcher(MatchEqual, "ghi", `three_four_five_six_seven_eight_"nine"_ten_one_two`),
+				MustNewMatcher(MatchEqual, "nop", `four_five_six_seven_eight_nine_"ten"_one_two_three`),
+			},
+		},
+		{
+			name: "long name regexp",
+			matchers: []*Matcher{
+				MustNewMatcher(MatchRegexp, "one_two_three_four_five_six_seven_eight_nine_ten", "val"),
+				MustNewMatcher(MatchRegexp, "two_three_four_five_six_seven_eight_nine_ten_one", "val"),
+				MustNewMatcher(MatchRegexp, "three_four_five_six_seven_eight_nine_ten_one_two", "val"),
+				MustNewMatcher(MatchRegexp, "four_five_six_seven_eight_nine_ten_one_two_three", "val"),
+				MustNewMatcher(MatchRegexp, "five_six_seven_eight_nine_ten_one_two_three_four", "val"),
+			},
+		},
+		{
+			name: "long quoted name regexp",
+			matchers: []*Matcher{
+				MustNewMatcher(MatchRegexp, "one.two.three.four.five.six.seven.eight.nine.ten", "val"),
+				MustNewMatcher(MatchRegexp, "two.three.four.five.six.seven.eight.nine.ten.one", "val"),
+				MustNewMatcher(MatchRegexp, "three.four.five.six.seven.eight.nine.ten.one.two", "val"),
+				MustNewMatcher(MatchRegexp, "four.five.six.seven.eight.nine.ten.one.two.three", "val"),
+				MustNewMatcher(MatchRegexp, "five.six.seven.eight.nine.ten.one.two.three.four", "val"),
+			},
+		},
+		{
+			name: "long name and long value regexp",
+			matchers: []*Matcher{
+				MustNewMatcher(MatchRegexp, "one_two_three_four_five_six_seven_eight_nine_ten", "five_six_seven_eight_nine_ten_one_two_three_four"),
+				MustNewMatcher(MatchRegexp, "two_three_four_five_six_seven_eight_nine_ten_one", "one_two_three_four_five_six_seven_eight_nine_ten"),
+				MustNewMatcher(MatchRegexp, "three_four_five_six_seven_eight_nine_ten_one_two", "two_three_four_five_six_seven_eight_nine_ten_one"),
+				MustNewMatcher(MatchRegexp, "four_five_six_seven_eight_nine_ten_one_two_three", "three_four_five_six_seven_eight_nine_ten_one_two"),
+				MustNewMatcher(MatchRegexp, "five_six_seven_eight_nine_ten_one_two_three_four", "four_five_six_seven_eight_nine_ten_one_two_three"),
+			},
+		},
+		{
+			name: "long quoted name and long value regexp",
+			matchers: []*Matcher{
+				MustNewMatcher(MatchRegexp, "one.two.three.four.five.six.seven.eight.nine.ten", "five.six.seven.eight.nine.ten.one.two.three.four"),
+				MustNewMatcher(MatchRegexp, "two.three.four.five.six.seven.eight.nine.ten.one", "one.two.three.four.five.six.seven.eight.nine.ten"),
+				MustNewMatcher(MatchRegexp, "three.four.five.six.seven.eight.nine.ten.one.two", "two.three.four.five.six.seven.eight.nine.ten.one"),
+				MustNewMatcher(MatchRegexp, "four.five.six.seven.eight.nine.ten.one.two.three", "three.four.five.six.seven.eight.nine.ten.one.two"),
+				MustNewMatcher(MatchRegexp, "five.six.seven.eight.nine.ten.one.two.three.four", "four.five.six.seven.eight.nine.ten.one.two.three"),
+			},
+		},
+	}
+
+	var mixed []*Matcher
+	for _, bc := range cases {
+		mixed = append(mixed, bc.matchers...)
+	}
+	rand.Shuffle(len(mixed), func(i, j int) { mixed[i], mixed[j] = mixed[j], mixed[i] })
+	cases = append(cases, benchCase{name: "mixed", matchers: mixed})
+
+	for _, bc := range cases {
+		b.Run(bc.name, func(b *testing.B) {
+			for i := 0; i <= b.N; i++ {
+				m := bc.matchers[i%len(bc.matchers)]
+				_ = m.String()
+			}
+		})
+	}
+}

promql/parser/printer_test.go

@@ -138,6 +138,16 @@ func TestExprString(t *testing.T) {
 		{
 			in: `{__name__="",a="x"}`,
 		},
+		{
+			in: `{"a.b"="c"}`,
+		},
+		{
+			in: `{"0"="1"}`,
+		},
+		{
+			in:  `{"_0"="1"}`,
+			out: `{_0="1"}`,
+		},
 	}
 
 	for _, test := range inputs {