1 files changed, 91 insertions, 0 deletions
diff --git a/src/go/printer/performance_test.go b/src/go/printer/performance_test.go
new file mode 100644
index 0000000..c58f6d4
--- /dev/null
+++ b/src/go/printer/performance_test.go
@@ -0,0 +1,91 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements a simple printer performance benchmark:
+// go test -bench=BenchmarkPrint
+
+package printer
+
+import (
+	"bytes"
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"io"
+	"log"
+	"os"
+	"testing"
+)
+
+var (
+	fileNode *ast.File
+	fileSize int64
+
+	declNode ast.Decl
+	declSize int64
+)
+
+func testprint(out io.Writer, node ast.Node) {
+	if err := (&Config{TabIndent | UseSpaces | normalizeNumbers, 8, 0}).Fprint(out, fset, node); err != nil {
+		log.Fatalf("print error: %s", err)
+	}
+}
+
+// cannot initialize in init because (printer) Fprint launches goroutines.
+func initialize() {
+	const filename = "testdata/parser.go"
+
+	src, err := os.ReadFile(filename)
+	if err != nil {
+		log.Fatalf("%s", err)
+	}
+
+	file, err := parser.ParseFile(fset, filename, src, parser.ParseComments)
+	if err != nil {
+		log.Fatalf("%s", err)
+	}
+
+	var buf bytes.Buffer
+	testprint(&buf, file)
+	if !bytes.Equal(buf.Bytes(), src) {
+		log.Fatalf("print error: %s not idempotent", filename)
+	}
+
+	fileNode = file
+	fileSize = int64(len(src))
+
+	for _, decl := range file.Decls {
+		// The first global variable, which is pretty short:
+		//
+		//	var unresolved = new(ast.Object)
+		if decl, ok := decl.(*ast.GenDecl); ok && decl.Tok == token.VAR {
+			declNode = decl
+			declSize = int64(fset.Position(decl.End()).Offset - fset.Position(decl.Pos()).Offset)
+			break
+		}
+
+	}
+}
+
+func BenchmarkPrintFile(b *testing.B) {
+	if fileNode == nil {
+		initialize()
+	}
+	b.ReportAllocs()
+	b.SetBytes(fileSize)
+	for i := 0; i < b.N; i++ {
+		testprint(io.Discard, fileNode)
+	}
+}
+
+func BenchmarkPrintDecl(b *testing.B) {
+	if declNode == nil {
+		initialize()
+	}
+	b.ReportAllocs()
+	b.SetBytes(declSize)
+	for i := 0; i < b.N; i++ {
+		testprint(io.Discard, declNode)
+	}
+}