cmd/dist: simplify code segments

This belongs to a series of clean-up changes (see below) for cmd/dist.
This is change (7).

These changes include:
(1)  apply minor fixes
(2)  restore behavior of branchtag
(3)  unleash bootstrap optimization for windows
(4)  use standard generated code header
(5)  remove trivial variables + functions
(6)  move functions for the better
(7)  simplify code segments
(8)  use bytes.Buffer for code generation
(9)  rename variables + functions
(10) remove doc.go

Change-Id: Ia3c33ef060b4baaef354b729ba82ed0b28e52857
Reviewed-on: https://go-review.googlesource.com/61013
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

4 files changed, 61 insertions, 67 deletions

diff --git a/src/cmd/dist/build.go b/src/cmd/dist/build.go
index 7b0c3a05e7..ddfe22fa50 100644
--- a/src/cmd/dist/build.go
+++ b/src/cmd/dist/build.go
@@ -43,8 +43,9 @@ var (
 	defaultcxxtarget       string
 	defaultcctarget        string
 	defaultpkgconfigtarget string
-	rebuildall             bool
-	defaultclang           bool
+
+	rebuildall   bool
+	defaultclang bool
 
 	vflag int // verbosity
 )
@@ -98,10 +99,11 @@ func xinit() {
 	}
 	goroot = filepath.Clean(b)
 
-	goroot_final = os.Getenv("GOROOT_FINAL")
-	if goroot_final == "" {
-		goroot_final = goroot
+	b = os.Getenv("GOROOT_FINAL")
+	if b == "" {
+		b = goroot
 	}
+	goroot_final = b
 
 	b = os.Getenv("GOBIN")
 	if b == "" {
@@ -134,8 +136,7 @@ func xinit() {
 	}
 	go386 = b
 
-	p := pathf("%s/src/all.bash", goroot)
-	if !isfile(p) {
+	if p := pathf("%s/src/all.bash", goroot); !isfile(p) {
 		fatal("$GOROOT is not set correctly or not exported\n"+
 			"\tGOROOT=%s\n"+
 			"\t%s does not exist", goroot, p)
@@ -145,7 +146,6 @@ func xinit() {
 	if b != "" {
 		gohostarch = b
 	}
-
 	if find(gohostarch, okgoarch) < 0 {
 		fatal("unknown $GOHOSTARCH %s", gohostarch)
 	}
@@ -253,20 +253,19 @@ func branchtag(branch string) (tag string, precise bool) {
 		// Each line is either blank, or looks like
 		//	  (tag: refs/tags/go1.4rc2, refs/remotes/origin/release-branch.go1.4, refs/heads/release-branch.go1.4)
 		// We need to find an element starting with refs/tags/.
-		i := strings.Index(line, " refs/tags/")
+		const s = " refs/tags/"
+		i := strings.Index(line, s)
 		if i < 0 {
 			continue
 		}
-		i += len(" refs/tags/")
-		// The tag name ends at a comma or paren (prefer the first).
-		j := strings.Index(line[i:], ",")
-		if j < 0 {
-			j = strings.Index(line[i:], ")")
-		}
+		// Trim off known prefix.
+		line = line[i+len(s):]
+		// The tag name ends at a comma or paren.
+		j := strings.IndexAny(line, ",)")
 		if j < 0 {
 			continue // malformed line; ignore it
 		}
-		tag = line[i : i+j]
+		tag = line[:j]
 		if row == 0 {
 			precise = true // tag denotes HEAD
 		}
@@ -339,8 +338,7 @@ func isGitRepo() bool {
 	if !filepath.IsAbs(gitDir) {
 		gitDir = filepath.Join(goroot, gitDir)
 	}
-	fi, err := os.Stat(gitDir)
-	return err == nil && fi.IsDir()
+	return isdir(gitDir)
 }
 
 /*
diff --git a/src/cmd/dist/buildgo.go b/src/cmd/dist/buildgo.go
index 79a9efba9c..f3e739b778 100644
--- a/src/cmd/dist/buildgo.go
+++ b/src/cmd/dist/buildgo.go
@@ -8,7 +8,9 @@ import (
 	"bytes"
 	"fmt"
 	"os"
+	"path/filepath"
 	"sort"
+	"strings"
 )
 
 /*
@@ -48,8 +50,7 @@ func mkzdefaultcc(dir, file string) {
 			"const defaultPkgConfig = `%s`\n",
 		defaultcctarget, defaultcxxtarget, defaultpkgconfigtarget)
 
-	i := len(file) - len("go/internal/cfg/zdefaultcc.go")
-	file = file[:i] + "cgo/zdefaultcc.go"
+	file = strings.Replace(file, filepath.FromSlash("go/internal/cfg"), "cgo", 1)
 	writefile(outCgo, file, writeSkipSame)
 }
 
@@ -63,13 +64,14 @@ func mkzosarch(dir, file string) {
 	sort.Strings(list)
 
 	var buf bytes.Buffer
-	buf.WriteString("// Code generated by go tool dist; DO NOT EDIT.\n\n")
-	buf.WriteString("package cfg\n\n")
+	fmt.Fprintf(&buf, "// Code generated by go tool dist; DO NOT EDIT.\n\n")
+	fmt.Fprintf(&buf, "package cfg\n\n")
 	fmt.Fprintf(&buf, "var OSArchSupportsCgo = map[string]bool{\n")
 	for _, plat := range list {
 		fmt.Fprintf(&buf, "\t%q: %v,\n", plat, cgoEnabled[plat])
 	}
 	fmt.Fprintf(&buf, "}\n")
+
 	writefile(buf.String(), file, writeSkipSame)
 }
 
diff --git a/src/cmd/dist/buildtool.go b/src/cmd/dist/buildtool.go
index 52307a3dc4..94f64be96f 100644
--- a/src/cmd/dist/buildtool.go
+++ b/src/cmd/dist/buildtool.go
@@ -128,8 +128,7 @@ func bootstrapBuildTools() {
 			}
 			srcFile := pathf("%s/%s", src, name)
 			dstFile := pathf("%s/%s", dst, name)
-			text := readfile(srcFile)
-			text = bootstrapRewriteFile(text, srcFile)
+			text := bootstrapRewriteFile(srcFile)
 			writefile(text, dstFile, 0)
 		}
 	}
@@ -221,7 +220,7 @@ func isUnneededSSARewriteFile(srcFile string) (archCaps string, unneeded bool) {
 	return archCaps, true
 }
 
-func bootstrapRewriteFile(text, srcFile string) string {
+func bootstrapRewriteFile(srcFile string) string {
 	// During bootstrap, generate dummy rewrite files for
 	// irrelevant architectures. We only need to build a bootstrap
 	// binary that works for the current runtime.GOARCH.
@@ -236,11 +235,11 @@ func rewriteBlock%s(b *Block) bool { panic("unused during bootstrap") }
 `, archCaps, archCaps)
 	}
 
-	return bootstrapFixImports(text, srcFile)
+	return bootstrapFixImports(srcFile)
 }
 
-func bootstrapFixImports(text, srcFile string) string {
-	lines := strings.SplitAfter(text, "\n")
+func bootstrapFixImports(srcFile string) string {
+	lines := strings.SplitAfter(readfile(srcFile), "\n")
 	inBlock := false
 	for i, line := range lines {
 		if strings.HasPrefix(line, "import (") {
diff --git a/src/cmd/dist/main.go b/src/cmd/dist/main.go
index 6f5e641739..20c0b18735 100644
--- a/src/cmd/dist/main.go
+++ b/src/cmd/dist/main.go
@@ -14,36 +14,33 @@ import (
 )
 
 func usage() {
-	xprintf("usage: go tool dist [command]\n" +
-		"Commands are:\n" +
-		"\n" +
-		"banner         print installation banner\n" +
-		"bootstrap      rebuild everything\n" +
-		"clean          deletes all built files\n" +
-		"env [-p]       print environment (-p: include $PATH)\n" +
-		"install [dir]  install individual directory\n" +
-		"list [-json]   list all supported platforms\n" +
-		"test [-h]      run Go test(s)\n" +
-		"version        print Go version\n" +
-		"\n" +
-		"All commands take -v flags to emit extra information.\n",
-	)
+	xprintf(`usage: go tool dist [command]
+Commands are:
+
+banner         print installation banner
+bootstrap      rebuild everything
+clean          deletes all built files
+env [-p]       print environment (-p: include $PATH)
+install [dir]  install individual directory
+list [-json]   list all supported platforms
+test [-h]      run Go test(s)
+version        print Go version
+
+All commands take -v flags to emit extra information.
+`)
 	xexit(2)
 }
 
-// cmdtab records the available commands.
-var cmdtab = []struct {
-	name string
-	f    func()
-}{
-	{"banner", cmdbanner},
-	{"bootstrap", cmdbootstrap},
-	{"clean", cmdclean},
-	{"env", cmdenv},
-	{"install", cmdinstall},
-	{"list", cmdlist},
-	{"test", cmdtest},
-	{"version", cmdversion},
+// commands records the available commands.
+var commands = map[string]func(){
+	"banner":    cmdbanner,
+	"bootstrap": cmdbootstrap,
+	"clean":     cmdclean,
+	"env":       cmdenv,
+	"install":   cmdinstall,
+	"list":      cmdlist,
+	"test":      cmdtest,
+	"version":   cmdversion,
 }
 
 // main takes care of OS-specific startup and dispatches to xmain.
@@ -172,17 +169,15 @@ func xmain() {
 	}
 	cmd := os.Args[1]
 	os.Args = os.Args[1:] // for flag parsing during cmd
-	for _, ct := range cmdtab {
-		if ct.name == cmd {
-			flag.Usage = func() {
-				fmt.Fprintf(os.Stderr, "usage: go tool dist %s [options]\n", cmd)
-				flag.PrintDefaults()
-				os.Exit(2)
-			}
-			ct.f()
-			return
-		}
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, "usage: go tool dist %s [options]\n", cmd)
+		flag.PrintDefaults()
+		os.Exit(2)
+	}
+	if f, ok := commands[cmd]; ok {
+		f()
+	} else {
+		xprintf("unknown command %s\n", cmd)
+		usage()
 	}
-	xprintf("unknown command %s\n", cmd)
-	usage()
 }