text/template/parse: use strings.Builder in Chain and List nodes

This CL is a continuation of 198078. Benchmark output:

benchmark                     old ns/op     new ns/op     delta
BenchmarkParseLarge-8         24759165      24516563      -0.98%
BenchmarkVariableString-8     115           115           +0.00%
BenchmarkListString-8         924           680           -26.41%

benchmark                     old allocs     new allocs     delta
BenchmarkVariableString-8     3              3              +0.00%
BenchmarkListString-8         14             13             -7.14%

benchmark                     old bytes     new bytes     delta
BenchmarkVariableString-8     72            72            +0.00%
BenchmarkListString-8         512           424           -17.19%

Change-Id: I9ec48fe4832437c556a5fa94d4cbf6e29e28d944
Reviewed-on: https://go-review.googlesource.com/c/go/+/198080Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/text/template/parse/node.go

@@ -7,7 +7,6 @@
 package parse
 
 import (
-	"bytes"
 	"fmt"
 	"strconv"
 	"strings"
@@ -94,11 +93,11 @@ func (l *ListNode) tree() *Tree {
 }
 
 func (l *ListNode) String() string {
-	b := new(bytes.Buffer)
+	var sb strings.Builder
 	for _, n := range l.Nodes {
-		fmt.Fprint(b, n)
+		sb.WriteString(n.String())
 	}
-	return b.String()
+	return sb.String()
 }
 
 func (l *ListNode) CopyList() *ListNode {
@@ -472,14 +471,19 @@ func (c *ChainNode) Add(field string) {
 }
 
 func (c *ChainNode) String() string {
-	s := c.Node.String()
+	var sb strings.Builder
 	if _, ok := c.Node.(*PipeNode); ok {
-		s = "(" + s + ")"
+		sb.WriteByte('(')
+		sb.WriteString(c.Node.String())
+		sb.WriteByte(')')
+	} else {
+		sb.WriteString(c.Node.String())
 	}
 	for _, field := range c.Field {
-		s += "." + field
+		sb.WriteByte('.')
+		sb.WriteString(field)
 	}
-	return s
+	return sb.String()
 }
 
 func (c *ChainNode) tree() *Tree {

src/text/template/parse/parse_test.go

@@ -554,7 +554,7 @@ func BenchmarkParseLarge(b *testing.B) {
 	}
 }
 
-var sink string
+var sinkv, sinkl string
 
 func BenchmarkVariableString(b *testing.B) {
 	v := &VariableNode{
@@ -563,9 +563,25 @@ func BenchmarkVariableString(b *testing.B) {
 	b.ResetTimer()
 	b.ReportAllocs()
 	for i := 0; i < b.N; i++ {
-		sink = v.String()
+		sinkv = v.String()
 	}
-	if sink == "" {
+	if sinkv == "" {
+		b.Fatal("Benchmark was not run")
+	}
+}
+
+func BenchmarkListString(b *testing.B) {
+	text := `{{ (printf .Field1.Field2.Field3).Value }}`
+	tree, err := New("bench").Parse(text, "", "", make(map[string]*Tree), builtins)
+	if err != nil {
+		b.Fatal(err)
+	}
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		sinkl = tree.Root.String()
+	}
+	if sinkl == "" {
 		b.Fatal("Benchmark was not run")
 	}
 }