misc/sortac: add tool to sort the AUTHORS and CONTRIBUTORS files

I keep losing this utility, used as part of other tools to auto-update
the AUTHORS and CONTRIBUTORS files.  Check it in to the repo so I
don't lose it, and so others can use it as well.

Updates #12042

Change-Id: Ib5886b85799087aaaddcec4c81169e2726322c05
Reviewed-on: https://go-review.googlesource.com/16824Reviewed-by: Russ Cox <rsc@golang.org>

misc/sortac/sortac.go

+// Copyright 2015 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.
+
+// Sortac sorts the AUTHORS and CONTRIBUTORS files.
+//
+// Usage:
+//
+//    sortac [file...]
+//
+// Sortac sorts the named files in place.
+// If given no arguments, it sorts standard input to standard output.
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+
+	"golang.org/x/text/collate"
+	"golang.org/x/text/language"
+)
+
+func main() {
+	log.SetFlags(0)
+	log.SetPrefix("sortac: ")
+	flag.Parse()
+
+	args := flag.Args()
+	if len(args) == 0 {
+		os.Stdout.Write(sortAC(os.Stdin))
+	} else {
+		for _, arg := range args {
+			f, err := os.Open(arg)
+			if err != nil {
+				log.Fatal(err)
+			}
+			sorted := sortAC(f)
+			f.Close()
+			if err := ioutil.WriteFile(arg, sorted, 0644); err != nil {
+				log.Fatal(err)
+			}
+		}
+	}
+}
+
+func sortAC(r io.Reader) []byte {
+	bs := bufio.NewScanner(r)
+	var header []string
+	var lines []string
+	for bs.Scan() {
+		t := bs.Text()
+		lines = append(lines, t)
+		if t == "# Please keep the list sorted." {
+			header = lines
+			lines = nil
+			continue
+		}
+	}
+	if err := bs.Err(); err != nil {
+		log.Fatal(err)
+	}
+
+	var out bytes.Buffer
+	c := collate.New(language.Und, collate.Loose)
+	c.SortStrings(lines)
+	for _, l := range header {
+		fmt.Fprintln(&out, l)
+	}
+	for _, l := range lines {
+		fmt.Fprintln(&out, l)
+	}
+	return out.Bytes()
+}