crypto/md5: use go generate to create md5block.go

LGTM=r
R=golang-codereviews, r
CC=golang-codereviews
https://golang.org/cl/129650043

src/pkg/crypto/md5/gen.go

@@ -7,7 +7,7 @@
 // This program generates md5block.go
 // Invoke as
 //
-//	go run gen.go [-full] |gofmt >md5block.go
+//	go run gen.go [-full] -output md5block.go
 //
 // The -full flag causes the generated code to do a full
 // (16x) unrolling instead of a 4x unrolling.
@@ -15,18 +15,33 @@
 package main
 
 import (
+	"bytes"
 	"flag"
+	"go/format"
+	"io/ioutil"
 	"log"
-	"os"
 	"strings"
 	"text/template"
 )
 
+var filename = flag.String("output", "md5block.go", "output file name")
+
 func main() {
 	flag.Parse()
 
+	var buf bytes.Buffer
+
 	t := template.Must(template.New("main").Funcs(funcs).Parse(program))
-	if err := t.Execute(os.Stdout, data); err != nil {
+	if err := t.Execute(&buf, data); err != nil {
+		log.Fatal(err)
+	}
+
+	data, err := format.Source(buf.Bytes())
+	if err != nil {
+		log.Fatal(err)
+	}
+	err = ioutil.WriteFile(*filename, data, 0644)
+	if err != nil {
 		log.Fatal(err)
 	}
 }
@@ -165,7 +180,7 @@ var program = `// Copyright 2013 The Go Authors. All rights reserved.
 // license that can be found in the LICENSE file.
 
 // DO NOT EDIT.
-// Generate with: go run gen.go{{if .Full}} -full{{end}} | gofmt >md5block.go
+// Generate with: go run gen.go{{if .Full}} -full{{end}} -output md5block.go
 
 package md5
 

src/pkg/crypto/md5/md5.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:generate go run gen.go -full -output md5block.go
+
 // Package md5 implements the MD5 hash algorithm as defined in RFC 1321.
 package md5
 

src/pkg/crypto/md5/md5block.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // DO NOT EDIT.
-// Generate with: go run gen.go -full | gofmt >md5block.go
+// Generate with: go run gen.go -full -output md5block.go
 
 package md5