cmd/dist: use bytes.Buffer for code generation

This belongs to a series of clean-up changes (see below) for cmd/dist.
This is change (8).

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: I2d5a071eb8e14690325612271432fdc5f43b108b
Reviewed-on: https://go-review.googlesource.com/61014
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 55 insertions, 57 deletions

diff --git a/src/cmd/dist/buildgo.go b/src/cmd/dist/buildgo.go
index f3e739b778..60cb24b6b5 100644
--- a/src/cmd/dist/buildgo.go
+++ b/src/cmd/dist/buildgo.go
@@ -27,31 +27,29 @@ import (
 // It is invoked to write cmd/go/internal/cfg/zdefaultcc.go
 // but we also write cmd/cgo/zdefaultcc.go
 func mkzdefaultcc(dir, file string) {
-	outGo := fmt.Sprintf(
-		"// Code generated by go tool dist; DO NOT EDIT.\n"+
-			"\n"+
-			"package cfg\n"+
-			"\n"+
-			"const DefaultCC = `%s`\n"+
-			"const DefaultCXX = `%s`\n"+
-			"const DefaultPkgConfig = `%s`\n",
-		defaultcctarget, defaultcxxtarget, defaultpkgconfigtarget)
+	var buf bytes.Buffer
+	fmt.Fprintf(&buf, "// Code generated by go tool dist; DO NOT EDIT.\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "package cfg\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "const DefaultCC = `%s`\n", defaultcctarget)
+	fmt.Fprintf(&buf, "const DefaultCXX = `%s`\n", defaultcxxtarget)
+	fmt.Fprintf(&buf, "const DefaultPkgConfig = `%s`\n", defaultpkgconfigtarget)
 
-	writefile(outGo, file, writeSkipSame)
+	writefile(buf.String(), file, writeSkipSame)
+	buf.Reset()
 
-	// Convert file name to replace: turn go/internal/cfg into cgo.
-	outCgo := fmt.Sprintf(
-		"// Code generated by go tool dist; DO NOT EDIT.\n"+
-			"\n"+
-			"package main\n"+
-			"\n"+
-			"const defaultCC = `%s`\n"+
-			"const defaultCXX = `%s`\n"+
-			"const defaultPkgConfig = `%s`\n",
-		defaultcctarget, defaultcxxtarget, defaultpkgconfigtarget)
+	fmt.Fprintf(&buf, "// Code generated by go tool dist; DO NOT EDIT.\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "package main\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "const defaultCC = `%s`\n", defaultcctarget)
+	fmt.Fprintf(&buf, "const defaultCXX = `%s`\n", defaultcxxtarget)
+	fmt.Fprintf(&buf, "const defaultPkgConfig = `%s`\n", defaultpkgconfigtarget)
 
+	// Convert file name.
 	file = strings.Replace(file, filepath.FromSlash("go/internal/cfg"), "cgo", 1)
-	writefile(outCgo, file, writeSkipSame)
+	writefile(buf.String(), file, writeSkipSame)
 }
 
 // mkzcgo writes zosarch.go for cmd/go.
@@ -92,14 +90,13 @@ func mkzcgo(dir, file string) {
 	sort.Strings(list)
 
 	var buf bytes.Buffer
-
-	fmt.Fprintf(&buf,
-		"// Code generated by go tool dist; DO NOT EDIT.\n"+
-			"\n"+
-			"package build\n"+
-			"\n"+
-			"const defaultCGO_ENABLED = %q\n\n"+
-			"var cgoEnabled = map[string]bool{\n", os.Getenv("CGO_ENABLED"))
+	fmt.Fprintf(&buf, "// Code generated by go tool dist; DO NOT EDIT.\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "package build\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "const defaultCGO_ENABLED = %q\n", os.Getenv("CGO_ENABLED"))
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "var cgoEnabled = map[string]bool{\n")
 	for _, plat := range list {
 		fmt.Fprintf(&buf, "\t%q: true,\n", plat)
 	}
diff --git a/src/cmd/dist/buildruntime.go b/src/cmd/dist/buildruntime.go
index 836b2ef31c..8dd095b82d 100644
--- a/src/cmd/dist/buildruntime.go
+++ b/src/cmd/dist/buildruntime.go
@@ -5,6 +5,7 @@
 package main
 
 import (
+	"bytes"
 	"fmt"
 	"os"
 	"strings"
@@ -24,17 +25,18 @@ import (
 //	const StackGuardMultiplier = <multiplier value>
 //
 func mkzversion(dir, file string) {
-	out := fmt.Sprintf(
-		"// Code generated by go tool dist; DO NOT EDIT.\n"+
-			"\n"+
-			"package sys\n"+
-			"\n"+
-			"var DefaultGoroot = `%s`\n\n"+
-			"const TheVersion = `%s`\n"+
-			"const Goexperiment = `%s`\n"+
-			"const StackGuardMultiplier = %d\n\n", goroot_final, findgoversion(), os.Getenv("GOEXPERIMENT"), stackGuardMultiplier())
+	var buf bytes.Buffer
+	fmt.Fprintf(&buf, "// Code generated by go tool dist; DO NOT EDIT.\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "package sys\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "var DefaultGoroot = `%s`\n", goroot_final)
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "const TheVersion = `%s`\n", findgoversion())
+	fmt.Fprintf(&buf, "const Goexperiment = `%s`\n", os.Getenv("GOEXPERIMENT"))
+	fmt.Fprintf(&buf, "const StackGuardMultiplier = %d\n", stackGuardMultiplier())
 
-	writefile(out, file, writeSkipSame)
+	writefile(buf.String(), file, writeSkipSame)
 }
 
 // mkzbootstrap writes cmd/internal/objabi/zbootstrap.go:
@@ -61,25 +63,24 @@ func mkzversion(dir, file string) {
 // This is more useful than having it default to generating objects for the
 // original target (in this example, a Mac).
 func mkzbootstrap(file string) {
-	out := fmt.Sprintf(
-		"// Code generated by go tool dist; DO NOT EDIT.\n"+
-			"\n"+
-			"package objabi\n"+
-			"\n"+
-			"import \"runtime\"\n"+
-			"\n"+
-			"const defaultGOROOT = `%s`\n"+
-			"const defaultGO386 = `%s`\n"+
-			"const defaultGOARM = `%s`\n"+
-			"const defaultGOOS = runtime.GOOS\n"+
-			"const defaultGOARCH = runtime.GOARCH\n"+
-			"const defaultGO_EXTLINK_ENABLED = `%s`\n"+
-			"const version = `%s`\n"+
-			"const stackGuardMultiplier = %d\n"+
-			"const goexperiment = `%s`\n",
-		goroot_final, go386, goarm, goextlinkenabled, findgoversion(), stackGuardMultiplier(), os.Getenv("GOEXPERIMENT"))
+	var buf bytes.Buffer
+	fmt.Fprintf(&buf, "// Code generated by go tool dist; DO NOT EDIT.\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "package objabi\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "import \"runtime\"\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "const defaultGOROOT = `%s`\n", goroot_final)
+	fmt.Fprintf(&buf, "const defaultGO386 = `%s`\n", go386)
+	fmt.Fprintf(&buf, "const defaultGOARM = `%s`\n", goarm)
+	fmt.Fprintf(&buf, "const defaultGOOS = runtime.GOOS\n")
+	fmt.Fprintf(&buf, "const defaultGOARCH = runtime.GOARCH\n")
+	fmt.Fprintf(&buf, "const defaultGO_EXTLINK_ENABLED = `%s`\n", goextlinkenabled)
+	fmt.Fprintf(&buf, "const version = `%s`\n", findgoversion())
+	fmt.Fprintf(&buf, "const stackGuardMultiplier = %d\n", stackGuardMultiplier())
+	fmt.Fprintf(&buf, "const goexperiment = `%s`\n", os.Getenv("GOEXPERIMENT"))
 
-	writefile(out, file, writeSkipSame)
+	writefile(buf.String(), file, writeSkipSame)
 }
 
 // stackGuardMultiplier returns a multiplier to apply to the default