LabelSet.String(): use different implementation for go 1.20

Signed-off-by: Arthur Silva Sens <arthur.sens@coralogix.com>

go.mod

@@ -1,6 +1,6 @@
 module github.com/prometheus/common
 
-go 1.21
+go 1.20
 
 require (
 	github.com/alecthomas/kingpin/v2 v2.4.0

model/labelset.go

@@ -14,12 +14,9 @@
 package model
 
 import (
-	"bytes"
 	"encoding/json"
 	"fmt"
-	"slices"
 	"sort"
-	"strconv"
 )
 
 // A LabelSet is a collection of LabelName and LabelValue pairs.  The LabelSet
@@ -131,29 +128,6 @@ func (l LabelSet) Merge(other LabelSet) LabelSet {
 	return result
 }
 
-// String will look like `{foo="bar", more="less"}`. Names are sorted alphabetically.
-func (l LabelSet) String() string {
-	var lna [32]LabelName // On stack to avoid memory allocation for sorting names.
-	labelNames := lna[:0]
-	for name := range l {
-		labelNames = append(labelNames, name)
-	}
-	slices.Sort(labelNames)
-	var bytea [1024]byte // On stack to avoid memory allocation while building the output.
-	b := bytes.NewBuffer(bytea[:0])
-	b.WriteByte('{')
-	for i, name := range labelNames {
-		if i > 0 {
-			b.WriteString(", ")
-		}
-		b.WriteString(string(name))
-		b.WriteByte('=')
-		b.Write(strconv.AppendQuote(b.AvailableBuffer(), string(l[name])))
-	}
-	b.WriteByte('}')
-	return b.String()
-}
-
 // Fingerprint returns the LabelSet's fingerprint.
 func (ls LabelSet) Fingerprint() Fingerprint {
 	return labelSetToFingerprint(ls)

model/labelset_go120_test.go

@@ -0,0 +1,144 @@
+// Copyright 2019 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build go1.20 && !go1.21
+
+package model
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestUnmarshalJSONLabelSet(t *testing.T) {
+	type testConfig struct {
+		LabelSet LabelSet `yaml:"labelSet,omitempty"`
+	}
+
+	// valid LabelSet JSON
+	labelSetJSON := `{
+	"labelSet": {
+		"monitor": "codelab",
+		"foo": "bar",
+		"foo2": "bar",
+		"abc": "prometheus",
+		"foo11": "bar11"
+	}
+}`
+	var c testConfig
+	err := json.Unmarshal([]byte(labelSetJSON), &c)
+	if err != nil {
+		t.Errorf("unexpected error while marshalling JSON : %s", err.Error())
+	}
+
+	labelSetString := c.LabelSet.String()
+
+	expected := `{abc="prometheus", foo="bar", foo11="bar11", foo2="bar", monitor="codelab"}`
+
+	if expected != labelSetString {
+		t.Errorf("expected %s but got %s", expected, labelSetString)
+	}
+
+	// invalid LabelSet JSON
+	invalidlabelSetJSON := `{
+	"labelSet": {
+		"1nvalid_23name": "codelab",
+		"foo": "bar"
+	}
+}`
+
+	NameValidationScheme = LegacyValidation
+	err = json.Unmarshal([]byte(invalidlabelSetJSON), &c)
+	expectedErr := `"1nvalid_23name" is not a valid label name`
+	if err == nil || err.Error() != expectedErr {
+		t.Errorf("expected an error with message '%s' to be thrown", expectedErr)
+	}
+}
+
+func TestLabelSetClone(t *testing.T) {
+	labelSet := LabelSet{
+		"monitor": "codelab",
+		"foo":     "bar",
+		"bar":     "baz",
+	}
+
+	cloneSet := labelSet.Clone()
+
+	if len(labelSet) != len(cloneSet) {
+		t.Errorf("expected the length of the cloned Label set to be %d, but got %d",
+			len(labelSet), len(cloneSet))
+	}
+
+	for ln, lv := range labelSet {
+		expected := cloneSet[ln]
+		if expected != lv {
+			t.Errorf("expected to get LabelValue %s, but got %s for LabelName %s", expected, lv, ln)
+		}
+	}
+}
+
+func TestLabelSetMerge(t *testing.T) {
+	labelSet := LabelSet{
+		"monitor": "codelab",
+		"foo":     "bar",
+		"bar":     "baz",
+	}
+
+	labelSet2 := LabelSet{
+		"monitor": "codelab",
+		"dolor":   "mi",
+		"lorem":   "ipsum",
+	}
+
+	expectedSet := LabelSet{
+		"monitor": "codelab",
+		"foo":     "bar",
+		"bar":     "baz",
+		"dolor":   "mi",
+		"lorem":   "ipsum",
+	}
+
+	mergedSet := labelSet.Merge(labelSet2)
+
+	if len(mergedSet) != len(expectedSet) {
+		t.Errorf("expected the length of the cloned Label set to be %d, but got %d",
+			len(expectedSet), len(mergedSet))
+	}
+
+	for ln, lv := range mergedSet {
+		expected := expectedSet[ln]
+		if expected != lv {
+			t.Errorf("expected to get LabelValue %s, but got %s for LabelName %s", expected, lv, ln)
+		}
+	}
+}
+
+// Benchmark Results for LabelSet's String() method
+// ---------------------------------------------------------------------------------------------------------
+// goos: linux
+// goarch: amd64
+// pkg: github.com/prometheus/common/model
+// cpu: 11th Gen Intel(R) Core(TM) i5-1145G7 @ 2.60GHz
+// BenchmarkLabelSetStringMethod-8                               732376              1532 ns/op
+
+func BenchmarkLabelSetStringMethod(b *testing.B) {
+	ls := make(LabelSet)
+	ls["monitor"] = "codelab"
+	ls["foo2"] = "bar"
+	ls["foo"] = "bar"
+	ls["abc"] = "prometheus"
+	ls["foo11"] = "bar11"
+	for i := 0; i < b.N; i++ {
+		_ = ls.String()
+	}
+}

model/labelset_string.go

@@ -0,0 +1,45 @@
+// Copyright 2013 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !go1.20
+
+package model
+
+import (
+	"bytes"
+	"sort"
+	"strconv"
+)
+
+// String will look like `{foo="bar", more="less"}`. Names are sorted alphabetically.
+func (l LabelSet) String() string {
+	var lna [32]string // On stack to avoid memory allocation for sorting names.
+	labelNames := lna[:0]
+	for name := range l {
+		labelNames = append(labelNames, string(name))
+	}
+	sort.Strings(labelNames)
+	var bytea [1024]byte // On stack to avoid memory allocation while building the output.
+	b := bytes.NewBuffer(bytea[:0])
+	b.WriteByte('{')
+	for i, name := range labelNames {
+		if i > 0 {
+			b.WriteString(", ")
+		}
+		b.WriteString(name)
+		b.WriteByte('=')
+		b.Write(strconv.AppendQuote(b.AvailableBuffer(), string(l[LabelName(name)])))
+	}
+	b.WriteByte('}')
+	return b.String()
+}

model/labelset_string_go120.go

@@ -0,0 +1,39 @@
+// Copyright 2013 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build go1.20 && !go1.21
+
+package model
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// String was optimized using functions not available for go 1.20
+// or lower. We keep the old implementation for compatibility with client_golang.
+// Once client golang drops support for go 1.20 (scheduled for August 2024), this
+// file can be removed.
+func (l LabelSet) String() string {
+	labelNames := make([]string, 0, len(l))
+	for name := range l {
+		labelNames = append(labelNames, string(name))
+	}
+	sort.Strings(labelNames)
+	lstrs := make([]string, 0, len(l))
+	for _, name := range labelNames {
+		lstrs = append(lstrs, fmt.Sprintf("%s=%q", name, l[LabelName(name)]))
+	}
+	return fmt.Sprintf("{%s}", strings.Join(lstrs, ", "))
+}

model/labelset_test.go

@@ -11,6 +11,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !go1.20
+
 package model
 
 import (