net/url: reduce allocs in Encode

src/net/url/url.go

@@ -15,7 +15,6 @@ package url
 import (
 	"errors"
 	"fmt"
-	"maps"
 	"net/netip"
 	"path"
 	"slices"
@@ -1048,7 +1047,14 @@ func (v Values) Encode() string {
 		return ""
 	}
 	var buf strings.Builder
-	for _, k := range slices.Sorted(maps.Keys(v)) {
+	// To minimize allocations, instead of using slices.Sorted(maps.Keys(v)),
+	// we pre-size the slice in which we collect v's keys and then sort it.
+	keys := make([]string, 0, len(v))
+	for k := range v {
+		keys = append(keys, k)
+	}
+	slices.Sort(keys)
+	for _, k := range keys {
 		vs := v[k]
 		keyEscaped := QueryEscape(k)
 		for _, v := range vs {

src/net/url/url_test.go

@@ -1101,6 +1101,15 @@ func TestEncodeQuery(t *testing.T) {
 	}
 }
 
+func BenchmarkEncodeQuery(b *testing.B) {
+	b.ReportAllocs()
+	for b.Loop() {
+		for _, tt := range encodeQueryTests {
+			tt.m.Encode()
+		}
+	}
+}
+
 var resolvePathTests = []struct {
 	base, ref, expected string
 }{