cmd/genbootstrap: new tool to generate minimal GOROOT_BOOTSTRAP tarballs

Fixes golang/go#9797

Change-Id: Ib8a8a5f9c0e51c22b93a1ba2957362e8fe829937
Reviewed-on: https://go-review.googlesource.com/21657
Reviewed-by: Andrew Gerrand <adg@golang.org>

cmd/genbootstrap/genbootstrap.go

@@ -0,0 +1,159 @@
+// Copyright 2016 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.
+
+/*
+The genbootstrap command prepares GO_BOOTSTRAP tarballs suitable for
+use on builders. It's a wrapper around bootstrap.bash. After
+bootstrap.bash produces the full output, genbootstrap trims it up,
+removing unnecessary and unwanted files.
+
+Usage:  genbootstrap GOOS/GOARCH
+*/
+package main
+
+import (
+	"flag"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+var skipBuild = flag.Bool("skip_build", false, "skip bootstrap.bash step; useful during development of cleaning code")
+
+func usage() {
+	log.Fatalf("Usage: genbootstrap GOOS/GOARCH")
+}
+
+func main() {
+	flag.Parse()
+	if flag.NArg() != 1 {
+		usage()
+	}
+	f := strings.Split(flag.Arg(0), "/")
+	if len(f) != 2 {
+		usage()
+	}
+	goos, goarch := f[0], f[1]
+	if os.Getenv("GOROOT") == "" {
+		log.Fatalf("GOROOT not set in environment")
+	}
+
+	tgz := filepath.Join(os.Getenv("GOROOT"), "src", "..", "..", "gobootstrap-"+goos+"-"+goarch+".tar.gz")
+	os.Remove(tgz)
+	outDir := filepath.Join(os.Getenv("GOROOT"), "src", "..", "..", "go-"+goos+"-"+goarch+"-bootstrap")
+	if !*skipBuild {
+		os.RemoveAll(outDir)
+		cmd := exec.Command(filepath.Join(os.Getenv("GOROOT"), "src", "bootstrap.bash"))
+		cmd.Dir = filepath.Join(os.Getenv("GOROOT"), "src")
+		cmd.Env = append(os.Environ(), "GOOS="+goos, "GOARCH="+goarch)
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		if err := cmd.Run(); err != nil {
+			log.Fatal(err)
+		}
+
+		// bootstrap.bash makes a bzipped tar file too, but it's fat and full of stuff we
+		// dont need it. delete it.
+		os.Remove(outDir + ".tbz")
+	}
+
+	if err := filepath.Walk(outDir, func(path string, fi os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		rel := strings.TrimPrefix(strings.TrimPrefix(path, outDir), "/")
+		base := filepath.Base(path)
+		var pkgrel string // relative to pkg/<goos>_<goarch>/, or empty
+		if strings.HasPrefix(rel, "pkg/") && strings.Count(rel, "/") >= 2 {
+			pkgrel = strings.TrimPrefix(rel, "pkg/")
+			pkgrel = pkgrel[strings.Index(pkgrel, "/")+1:]
+			log.Printf("rel %q => %q", rel, pkgrel)
+		}
+		remove := func() error {
+			if err := os.RemoveAll(path); err != nil {
+				return err
+			}
+			if fi.IsDir() {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+		switch pkgrel {
+		case "cmd",
+			"database", "database.a",
+			"image", "image.a",
+			"net.a",
+			"net",
+			"runtime/cgo.a",
+			"vendor/golang.org/x/net":
+			return remove()
+		}
+		switch rel {
+		case "api",
+			"bin/gofmt",
+			"doc",
+			"misc/android",
+			"misc/cgo",
+			"misc/chrome",
+			"misc/swig",
+			"src/cmd",
+			"src/net",
+			"src/runtime/cgo",
+			"src/database",
+			"src/image",
+			"src/vendor/golang.org/x/net",
+			"test":
+			return remove()
+		}
+		if base == "testdata" {
+			return remove()
+		}
+		if strings.HasPrefix(rel, "pkg/tool/") {
+			switch base {
+			case "addr2line", "api", "cgo", "cover",
+				"dist", "doc", "fix", "nm",
+				"objdump", "pack", "pprof",
+				"trace", "vet", "yacc":
+				return remove()
+			}
+		}
+		if fi.IsDir() {
+			return nil
+		}
+		if isEditorJunkFile(path) {
+			return remove()
+		}
+		if !fi.Mode().IsRegular() {
+			return remove()
+		}
+		if strings.HasSuffix(path, "_test.go") {
+			return remove()
+		}
+		log.Printf("keeping: %s\n", rel)
+		return nil
+	}); err != nil {
+		log.Fatal(err)
+	}
+
+	log.Printf("Running: tar zcf %s .", tgz)
+	cmd := exec.Command("tar", "zcf", tgz, ".")
+	cmd.Dir = outDir
+	if err := cmd.Run(); err != nil {
+		log.Fatalf("tar zf failed: %v", err)
+	}
+	log.Printf("Done. Output is %s", tgz)
+}
+
+func isEditorJunkFile(path string) bool {
+	path = filepath.Base(path)
+	if strings.HasPrefix(path, "#") && strings.HasSuffix(path, "#") {
+		return true
+	}
+	if strings.HasSuffix(path, "~") {
+		return true
+	}
+	return false
+}