image/color/palette: use go generate to create palette.go

LGTM=r
R=golang-codereviews, r
CC=golang-codereviews
https://golang.org/cl/134940043

src/pkg/image/color/palette/gen.go

@@ -7,29 +7,49 @@
 package main
 
 // This program generates palette.go. Invoke it as
-//	go run gen.go | gofmt > palette.go
+//	go run gen.go -output palette.go
 
 import (
+	"bytes"
+	"flag"
 	"fmt"
+	"go/format"
+	"io"
+	"io/ioutil"
+	"log"
 )
 
+var filename = flag.String("output", "palette.go", "output file name")
+
 func main() {
-	fmt.Println(`// Copyright 2013 The Go Authors. All rights reserved.
+	flag.Parse()
+
+	var buf bytes.Buffer
+
+	fmt.Fprintln(&buf, `// Copyright 2013 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.`)
-	fmt.Println()
-	fmt.Println("// generated by go run gen.go; DO NOT EDIT")
-	fmt.Println()
-	fmt.Println("// Package palette provides standard color palettes.")
-	fmt.Println("package palette")
-	fmt.Println()
-	fmt.Println(`import "image/color"`)
-	fmt.Println()
-	printPlan9()
-	printWebSafe()
+	fmt.Fprintln(&buf)
+	fmt.Fprintln(&buf, "// generated by go run gen.go -output palette.go; DO NOT EDIT")
+	fmt.Fprintln(&buf)
+	fmt.Fprintln(&buf, "package palette")
+	fmt.Fprintln(&buf)
+	fmt.Fprintln(&buf, `import "image/color"`)
+	fmt.Fprintln(&buf)
+	printPlan9(&buf)
+	printWebSafe(&buf)
+
+	data, err := format.Source(buf.Bytes())
+	if err != nil {
+		log.Fatal(err)
+	}
+	err = ioutil.WriteFile(*filename, data, 0644)
+	if err != nil {
+		log.Fatal(err)
+	}
 }
 
-func printPlan9() {
+func printPlan9(w io.Writer) {
 	c, lines := [3]int{}, [256]string{}
 	for r, i := 0, 0; r != 4; r++ {
 		for v := 0; v != 4; v, i = v+1, i+16 {
@@ -58,27 +78,27 @@ func printPlan9() {
 			}
 		}
 	}
-	fmt.Println("// Plan9 is a 256-color palette that partitions the 24-bit RGB space")
-	fmt.Println("// into 4×4×4 subdivision, with 4 shades in each subcube. Compared to the")
-	fmt.Println("// WebSafe, the idea is to reduce the color resolution by dicing the")
-	fmt.Println("// color cube into fewer cells, and to use the extra space to increase the")
-	fmt.Println("// intensity resolution. This results in 16 gray shades (4 gray subcubes with")
-	fmt.Println("// 4 samples in each), 13 shades of each primary and secondary color (3")
-	fmt.Println("// subcubes with 4 samples plus black) and a reasonable selection of colors")
-	fmt.Println("// covering the rest of the color cube. The advantage is better representation")
-	fmt.Println("// of continuous tones.")
-	fmt.Println("//")
-	fmt.Println("// This palette was used in the Plan 9 Operating System, described at")
-	fmt.Println("// http://plan9.bell-labs.com/magic/man2html/6/color")
-	fmt.Println("var Plan9 = []color.Color{")
+	fmt.Fprintln(w, "// Plan9 is a 256-color palette that partitions the 24-bit RGB space")
+	fmt.Fprintln(w, "// into 4×4×4 subdivision, with 4 shades in each subcube. Compared to the")
+	fmt.Fprintln(w, "// WebSafe, the idea is to reduce the color resolution by dicing the")
+	fmt.Fprintln(w, "// color cube into fewer cells, and to use the extra space to increase the")
+	fmt.Fprintln(w, "// intensity resolution. This results in 16 gray shades (4 gray subcubes with")
+	fmt.Fprintln(w, "// 4 samples in each), 13 shades of each primary and secondary color (3")
+	fmt.Fprintln(w, "// subcubes with 4 samples plus black) and a reasonable selection of colors")
+	fmt.Fprintln(w, "// covering the rest of the color cube. The advantage is better representation")
+	fmt.Fprintln(w, "// of continuous tones.")
+	fmt.Fprintln(w, "//")
+	fmt.Fprintln(w, "// This palette was used in the Plan 9 Operating System, described at")
+	fmt.Fprintln(w, "// http://plan9.bell-labs.com/magic/man2html/6/color")
+	fmt.Fprintln(w, "var Plan9 = []color.Color{")
 	for _, line := range lines {
-		fmt.Println(line)
+		fmt.Fprintln(w, line)
 	}
-	fmt.Println("}")
-	fmt.Println()
+	fmt.Fprintln(w, "}")
+	fmt.Fprintln(w)
 }
 
-func printWebSafe() {
+func printWebSafe(w io.Writer) {
 	lines := [6 * 6 * 6]string{}
 	for r := 0; r < 6; r++ {
 		for g := 0; g < 6; g++ {
@@ -88,14 +108,14 @@ func printWebSafe() {
 			}
 		}
 	}
-	fmt.Println("// WebSafe is a 216-color palette that was popularized by early versions")
-	fmt.Println("// of Netscape Navigator. It is also known as the Netscape Color Cube.")
-	fmt.Println("//")
-	fmt.Println("// See http://en.wikipedia.org/wiki/Web_colors#Web-safe_colors for details.")
-	fmt.Println("var WebSafe = []color.Color{")
+	fmt.Fprintln(w, "// WebSafe is a 216-color palette that was popularized by early versions")
+	fmt.Fprintln(w, "// of Netscape Navigator. It is also known as the Netscape Color Cube.")
+	fmt.Fprintln(w, "//")
+	fmt.Fprintln(w, "// See http://en.wikipedia.org/wiki/Web_colors#Web-safe_colors for details.")
+	fmt.Fprintln(w, "var WebSafe = []color.Color{")
 	for _, line := range lines {
-		fmt.Println(line)
+		fmt.Fprintln(w, line)
 	}
-	fmt.Println("}")
-	fmt.Println()
+	fmt.Fprintln(w, "}")
+	fmt.Fprintln(w)
 }

src/pkg/image/color/palette/generate.go

@@ -0,0 +1,8 @@
+// Copyright 2014 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.
+
+//go:generate go run gen.go -output palette.go
+
+// Package palette provides standard color palettes.
+package palette

src/pkg/image/color/palette/palette.go

@@ -2,9 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// generated by go run gen.go; DO NOT EDIT
+// generated by go run gen.go -output palette.go; DO NOT EDIT
 
-// Package palette provides standard color palettes.
 package palette
 
 import "image/color"