LabelSet: Fix alphabetical sorting for prometheus LabelSet

model/labelset.go

@@ -130,12 +130,15 @@ func (l LabelSet) Merge(other LabelSet) LabelSet {
 }
 
 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 l, v := range l {
-		lstrs = append(lstrs, fmt.Sprintf("%s=%q", l, v))
+	for _, name := range labelNames {
+		lstrs = append(lstrs, fmt.Sprintf("%s=%q", name, l[LabelName(name)]))
 	}
-
-	sort.Strings(lstrs)
 	return fmt.Sprintf("{%s}", strings.Join(lstrs, ", "))
 }
 

model/labelset_test.go

@@ -27,7 +27,10 @@ func TestUnmarshalJSONLabelSet(t *testing.T) {
 	labelSetJSON := `{
 	"labelSet": {
 		"monitor": "codelab",
-		"foo": "bar"
+		"foo": "bar",
+		"foo2": "bar",
+		"abc": "prometheus",
+		"foo11": "bar11"
 	}
 }`
 	var c testConfig
@@ -38,7 +41,7 @@ func TestUnmarshalJSONLabelSet(t *testing.T) {
 
 	labelSetString := c.LabelSet.String()
 
-	expected := `{foo="bar", monitor="codelab"}`
+	expected := `{abc="prometheus", foo="bar", foo11="bar11", foo2="bar", monitor="codelab"}`
 
 	if expected != labelSetString {
 		t.Errorf("expected %s but got %s", expected, labelSetString)
@@ -117,3 +120,23 @@ func TestLabelSetMerge(t *testing.T) {
 		}
 	}
 }
+
+// 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()
+	}
+}