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/+/198080
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 19 insertions, 3 deletions

diff --git a/src/text/template/parse/parse_test.go b/src/text/template/parse/parse_test.go
index 371de5d67c..86a100bb5f 100644
--- a/src/text/template/parse/parse_test.go
+++ b/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")
 	}
 }