goinstall: use go/make package to scan and build packages

R=rsc, n13m3y3r, kevlar
CC=golang-dev
https://golang.org/cl/4515180

11 files changed, 214 insertions, 644 deletions

diff --git a/src/cmd/goinstall/Makefile b/src/cmd/goinstall/Makefile
index 202797cd56..399d294adc 100644
--- a/src/cmd/goinstall/Makefile
+++ b/src/cmd/goinstall/Makefile
@@ -8,23 +8,5 @@ TARG=goinstall
 GOFILES=\
 	download.go\
 	main.go\
-	make.go\
-	parse.go\
-	path.go\
-	syslist.go\
-
-CLEANFILES+=syslist.go
 
 include ../../Make.cmd
-
-syslist.go:
-	echo '// Generated automatically by make.' >$@
-	echo 'package main' >>$@
-	echo 'const goosList = "$(GOOS_LIST)"' >>$@
-	echo 'const goarchList = "$(GOARCH_LIST)"' >>$@
-
-test:
-	gotest
-
-testshort:
-	gotest -test.short
diff --git a/src/cmd/goinstall/doc.go b/src/cmd/goinstall/doc.go
index 13c37d0a23..649117be07 100644
--- a/src/cmd/goinstall/doc.go
+++ b/src/cmd/goinstall/doc.go
@@ -15,7 +15,9 @@ Flags and default settings:
         -a=false          install all previously installed packages
 	-clean=false      clean the package directory before installing
 	-dashboard=true   tally public packages on godashboard.appspot.com
+	-install=true     build and install the package and its dependencies
 	-log=true         log installed packages to $GOROOT/goinstall.log for use by -a
+	-nuke=false       remove the target object and clean before installing
 	-u=false          update already-downloaded packages
 	-v=false          verbose operation
 
diff --git a/src/cmd/goinstall/main.go b/src/cmd/goinstall/main.go
index 721e719d26..6ff37df3c0 100644
--- a/src/cmd/goinstall/main.go
+++ b/src/cmd/goinstall/main.go
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Experimental Go package installer; see doc.go.
-
 package main
 
 import (
@@ -11,6 +9,7 @@ import (
 	"exec"
 	"flag"
 	"fmt"
+	"go/build"
 	"go/token"
 	"io/ioutil"
 	"os"
@@ -39,7 +38,9 @@ var (
 	reportToDashboard = flag.Bool("dashboard", true, "report public packages at "+dashboardURL)
 	logPkgs           = flag.Bool("log", true, "log installed packages to $GOROOT/goinstall.log for use by -a")
 	update            = flag.Bool("u", false, "update already-downloaded packages")
+	doInstall         = flag.Bool("install", true, "build and install")
 	clean             = flag.Bool("clean", false, "clean the package directory before installing")
+	nuke              = flag.Bool("nuke", false, "clean the package directory and target before installing")
 	verbose           = flag.Bool("v", false, "verbose")
 )
 
@@ -160,66 +161,83 @@ func install(pkg, parent string) {
 		fmt.Fprintf(os.Stderr, "\t%s\n", pkg)
 		os.Exit(2)
 	}
-	visit[pkg] = visiting
 	parents[pkg] = parent
-
-	vlogf("%s: visit\n", pkg)
+	visit[pkg] = visiting
+	defer func() {
+		visit[pkg] = done
+	}()
 
 	// Check whether package is local or remote.
 	// If remote, download or update it.
-	proot, pkg, err := findPackageRoot(pkg)
+	tree, pkg, err := build.FindTree(pkg)
 	// Don't build the standard library.
-	if err == nil && proot.goroot && isStandardPath(pkg) {
+	if err == nil && tree.Goroot && isStandardPath(pkg) {
 		if parent == "" {
 			errorf("%s: can not goinstall the standard library\n", pkg)
 		} else {
 			vlogf("%s: skipping standard library\n", pkg)
 		}
-		visit[pkg] = done
 		return
 	}
 	// Download remote packages if not found or forced with -u flag.
 	remote := isRemote(pkg)
-	if remote && (err == ErrPackageNotFound || (err == nil && *update)) {
+	if remote && (err == build.ErrNotFound || (err == nil && *update)) {
 		vlogf("%s: download\n", pkg)
-		err = download(pkg, proot.srcDir())
+		err = download(pkg, tree.SrcDir())
 	}
 	if err != nil {
 		errorf("%s: %v\n", pkg, err)
-		visit[pkg] = done
 		return
 	}
-	dir := filepath.Join(proot.srcDir(), pkg)
+	dir := filepath.Join(tree.SrcDir(), pkg)
 
 	// Install prerequisites.
-	dirInfo, err := scanDir(dir, parent == "")
+	dirInfo, err := build.ScanDir(dir, parent == "")
 	if err != nil {
 		errorf("%s: %v\n", pkg, err)
-		visit[pkg] = done
 		return
 	}
-	if len(dirInfo.goFiles) == 0 {
+	if len(dirInfo.GoFiles) == 0 {
 		errorf("%s: package has no files\n", pkg)
-		visit[pkg] = done
 		return
 	}
-	for _, p := range dirInfo.imports {
+	for _, p := range dirInfo.Imports {
 		if p != "C" {
 			install(p, pkg)
 		}
 	}
+	if errors {
+		return
+	}
 
 	// Install this package.
-	if !errors {
-		isCmd := dirInfo.pkgName == "main"
-		if err := domake(dir, pkg, proot, isCmd); err != nil {
-			errorf("installing: %v\n", err)
-		} else if remote && *logPkgs {
-			// mark package as installed in $GOROOT/goinstall.log
-			logPackage(pkg)
+	script, err := build.Build(tree, pkg, dirInfo)
+	if err != nil {
+		errorf("%s: install: %v\n", pkg, err)
+		return
+	}
+	if *nuke {
+		vlogf("%s: nuke\n", pkg)
+		script.Nuke()
+	} else if *clean {
+		vlogf("%s: clean\n", pkg)
+		script.Clean()
+	}
+	if *doInstall {
+		if script.Stale() {
+			vlogf("%s: install\n", pkg)
+			if err := script.Run(); err != nil {
+				errorf("%s: install: %v\n", pkg, err)
+				return
+			}
+		} else {
+			vlogf("%s: install: up-to-date\n", pkg)
 		}
 	}
-	visit[pkg] = done
+	if remote {
+		// mark package as installed in $GOROOT/goinstall.log
+		logPackage(pkg)
+	}
 }
 
 
diff --git a/src/cmd/goinstall/make.go b/src/cmd/goinstall/make.go
deleted file mode 100644
index 0c44481d71..0000000000
--- a/src/cmd/goinstall/make.go
+++ /dev/null
@@ -1,168 +0,0 @@
-// Copyright 2010 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.
-
-// Run "make install" to build package.
-
-package main
-
-import (
-	"bytes"
-	"os"
-	"path/filepath"
-	"template"
-)
-
-// domake builds the package in dir.
-// domake generates a standard Makefile and passes it
-// to make on standard input.
-func domake(dir, pkg string, root *pkgroot, isCmd bool) (err os.Error) {
-	makefile, err := makeMakefile(dir, pkg, root, isCmd)
-	if err != nil {
-		return err
-	}
-	cmd := []string{"bash", "gomake", "-f-"}
-	if *clean {
-		cmd = append(cmd, "clean")
-	}
-	cmd = append(cmd, "install")
-	return run(dir, makefile, cmd...)
-}
-
-// makeMakefile computes the standard Makefile for the directory dir
-// installing as package pkg.  It includes all *.go files in the directory
-// except those in package main and those ending in _test.go.
-func makeMakefile(dir, pkg string, root *pkgroot, isCmd bool) ([]byte, os.Error) {
-	if !safeName(pkg) {
-		return nil, os.ErrorString("unsafe name: " + pkg)
-	}
-	targ := pkg
-	targDir := root.pkgDir()
-	if isCmd {
-		// use the last part of the package name for targ
-		_, targ = filepath.Split(pkg)
-		targDir = root.binDir()
-	}
-	dirInfo, err := scanDir(dir, isCmd)
-	if err != nil {
-		return nil, err
-	}
-
-	cgoFiles := dirInfo.cgoFiles
-	isCgo := make(map[string]bool, len(cgoFiles))
-	for _, file := range cgoFiles {
-		if !safeName(file) {
-			return nil, os.ErrorString("bad name: " + file)
-		}
-		isCgo[file] = true
-	}
-
-	goFiles := make([]string, 0, len(dirInfo.goFiles))
-	for _, file := range dirInfo.goFiles {
-		if !safeName(file) {
-			return nil, os.ErrorString("unsafe name: " + file)
-		}
-		if !isCgo[file] {
-			goFiles = append(goFiles, file)
-		}
-	}
-
-	oFiles := make([]string, 0, len(dirInfo.cFiles)+len(dirInfo.sFiles))
-	cgoOFiles := make([]string, 0, len(dirInfo.cFiles))
-	for _, file := range dirInfo.cFiles {
-		if !safeName(file) {
-			return nil, os.ErrorString("unsafe name: " + file)
-		}
-		// When cgo is in use, C files are compiled with gcc,
-		// otherwise they're compiled with gc.
-		if len(cgoFiles) > 0 {
-			cgoOFiles = append(cgoOFiles, file[:len(file)-2]+".o")
-		} else {
-			oFiles = append(oFiles, file[:len(file)-2]+".$O")
-		}
-	}
-
-	for _, file := range dirInfo.sFiles {
-		if !safeName(file) {
-			return nil, os.ErrorString("unsafe name: " + file)
-		}
-		oFiles = append(oFiles, file[:len(file)-2]+".$O")
-	}
-
-	var buf bytes.Buffer
-	md := makedata{targ, targDir, "pkg", goFiles, oFiles, cgoFiles, cgoOFiles, imports}
-	if isCmd {
-		md.Type = "cmd"
-	}
-	if err := makefileTemplate.Execute(&buf, &md); err != nil {
-		return nil, err
-	}
-	return buf.Bytes(), nil
-}
-
-var safeBytes = []byte("+-./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz")
-
-func safeName(s string) bool {
-	if s == "" {
-		return false
-	}
-	for i := 0; i < len(s); i++ {
-		if c := s[i]; c < 0x80 && bytes.IndexByte(safeBytes, c) < 0 {
-			return false
-		}
-	}
-	return true
-}
-
-// makedata is the data type for the makefileTemplate.
-type makedata struct {
-	Targ      string   // build target
-	TargDir   string   // build target directory
-	Type      string   // build type: "pkg" or "cmd"
-	GoFiles   []string // list of non-cgo .go files
-	OFiles    []string // list of .$O files
-	CgoFiles  []string // list of cgo .go files
-	CgoOFiles []string // list of cgo .o files, without extension
-	Imports   []string // gc/ld import paths
-}
-
-var makefileTemplate = template.MustParse(`
-include $(GOROOT)/src/Make.inc
-
-TARG={Targ}
-TARGDIR={TargDir}
-
-{.section GoFiles}
-GOFILES=\
-{.repeated section GoFiles}
-	{@}\
-{.end}
-
-{.end}
-{.section OFiles}
-OFILES=\
-{.repeated section OFiles}
-	{@}\
-{.end}
-
-{.end}
-{.section CgoFiles}
-CGOFILES=\
-{.repeated section CgoFiles}
-	{@}\
-{.end}
-
-{.end}
-{.section CgoOFiles}
-CGO_OFILES=\
-{.repeated section CgoOFiles}
-	{@}\
-{.end}
-
-{.end}
-GCIMPORTS={.repeated section Imports}-I "{@}" {.end}
-LDIMPORTS={.repeated section Imports}-L "{@}" {.end}
-
-include $(GOROOT)/src/Make.{Type}
-`,
-	nil)
diff --git a/src/cmd/goinstall/parse.go b/src/cmd/goinstall/parse.go
deleted file mode 100644
index a4bb761f2b..0000000000
--- a/src/cmd/goinstall/parse.go
+++ /dev/null
@@ -1,172 +0,0 @@
-// Copyright 2010 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.
-
-// Wrappers for Go parser.
-
-package main
-
-import (
-	"go/ast"
-	"go/parser"
-	"log"
-	"os"
-	"path/filepath"
-	"strconv"
-	"strings"
-	"runtime"
-)
-
-
-type dirInfo struct {
-	goFiles  []string // .go files within dir (including cgoFiles)
-	cgoFiles []string // .go files that import "C"
-	cFiles   []string // .c files within dir
-	sFiles   []string // .s files within dir
-	imports  []string // All packages imported by goFiles
-	pkgName  string   // Name of package within dir
-}
-
-// scanDir returns a structure with details about the Go content found
-// in the given directory. The list of files will NOT contain the
-// following entries:
-//
-// - Files in package main (unless allowMain is true)
-// - Files ending in _test.go
-// - Files starting with _ (temporary)
-// - Files containing .cgo in their names
-//
-// The imports map keys are package paths imported by listed Go files,
-// and the values are the Go files importing the respective package paths.
-func scanDir(dir string, allowMain bool) (info *dirInfo, err os.Error) {
-	f, err := os.Open(dir)
-	if err != nil {
-		return nil, err
-	}
-	dirs, err := f.Readdir(-1)
-	f.Close()
-	if err != nil {
-		return nil, err
-	}
-
-	goFiles := make([]string, 0, len(dirs))
-	cgoFiles := make([]string, 0, len(dirs))
-	cFiles := make([]string, 0, len(dirs))
-	sFiles := make([]string, 0, len(dirs))
-	importsm := make(map[string]bool)
-	pkgName := ""
-	for i := range dirs {
-		d := &dirs[i]
-		if strings.HasPrefix(d.Name, "_") || strings.Index(d.Name, ".cgo") != -1 {
-			continue
-		}
-		if !goodOSArch(d.Name) {
-			continue
-		}
-
-		switch filepath.Ext(d.Name) {
-		case ".go":
-			if strings.HasSuffix(d.Name, "_test.go") {
-				continue
-			}
-		case ".c":
-			cFiles = append(cFiles, d.Name)
-			continue
-		case ".s":
-			sFiles = append(sFiles, d.Name)
-			continue
-		default:
-			continue
-		}
-
-		filename := filepath.Join(dir, d.Name)
-		pf, err := parser.ParseFile(fset, filename, nil, parser.ImportsOnly)
-		if err != nil {
-			return nil, err
-		}
-		s := string(pf.Name.Name)
-		if s == "main" && !allowMain {
-			continue
-		}
-		if s == "documentation" {
-			continue
-		}
-		if pkgName == "" {
-			pkgName = s
-		} else if pkgName != s {
-			// Only if all files in the directory are in package main
-			// do we return pkgName=="main".
-			// A mix of main and another package reverts
-			// to the original (allowMain=false) behaviour.
-			if s == "main" || pkgName == "main" {
-				return scanDir(dir, false)
-			}
-			return nil, os.ErrorString("multiple package names in " + dir)
-		}
-		goFiles = append(goFiles, d.Name)
-		for _, decl := range pf.Decls {
-			for _, spec := range decl.(*ast.GenDecl).Specs {
-				quoted := string(spec.(*ast.ImportSpec).Path.Value)
-				unquoted, err := strconv.Unquote(quoted)
-				if err != nil {
-					log.Panicf("%s: parser returned invalid quoted string: <%s>", filename, quoted)
-				}
-				importsm[unquoted] = true
-				if unquoted == "C" {
-					cgoFiles = append(cgoFiles, d.Name)
-				}
-			}
-		}
-	}
-	imports := make([]string, len(importsm))
-	i := 0
-	for p := range importsm {
-		imports[i] = p
-		i++
-	}
-	return &dirInfo{goFiles, cgoFiles, cFiles, sFiles, imports, pkgName}, nil
-}
-
-// goodOSArch returns false if the filename contains a $GOOS or $GOARCH
-// suffix which does not match the current system.
-// The recognized filename formats are:
-//
-//     name_$(GOOS).*
-//     name_$(GOARCH).*
-//     name_$(GOOS)_$(GOARCH).*
-//
-func goodOSArch(filename string) bool {
-	if dot := strings.Index(filename, "."); dot != -1 {
-		filename = filename[:dot]
-	}
-	l := strings.Split(filename, "_", -1)
-	n := len(l)
-	if n == 0 {
-		return true
-	}
-	if good, known := goodOS[l[n-1]]; known {
-		return good
-	}
-	if good, known := goodArch[l[n-1]]; known {
-		if !good || n < 2 {
-			return false
-		}
-		good, known = goodOS[l[n-2]]
-		return good || !known
-	}
-	return true
-}
-
-var goodOS = make(map[string]bool)
-var goodArch = make(map[string]bool)
-
-func init() {
-	goodOS = make(map[string]bool)
-	goodArch = make(map[string]bool)
-	for _, v := range strings.Fields(goosList) {
-		goodOS[v] = v == runtime.GOOS
-	}
-	for _, v := range strings.Fields(goarchList) {
-		goodArch[v] = v == runtime.GOARCH
-	}
-}
diff --git a/src/cmd/goinstall/path.go b/src/cmd/goinstall/path.go
deleted file mode 100644
index b8c3929316..0000000000
--- a/src/cmd/goinstall/path.go
+++ /dev/null
@@ -1,149 +0,0 @@
-// Copyright 2011 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.
-
-package main
-
-import (
-	"fmt"
-	"log"
-	"os"
-	"path/filepath"
-	"runtime"
-	"strings"
-)
-
-var (
-	gopath      []*pkgroot
-	imports     []string
-	defaultRoot *pkgroot // default root for remote packages
-)
-
-// set up gopath: parse and validate GOROOT and GOPATH variables
-func init() {
-	root := runtime.GOROOT()
-	p, err := newPkgroot(root)
-	if err != nil {
-		log.Fatalf("Invalid GOROOT %q: %v", root, err)
-	}
-	p.goroot = true
-	gopath = []*pkgroot{p}
-
-	for _, p := range filepath.SplitList(os.Getenv("GOPATH")) {
-		if p == "" {
-			continue
-		}
-		r, err := newPkgroot(p)
-		if err != nil {
-			log.Printf("Invalid GOPATH %q: %v", p, err)
-			continue
-		}
-		gopath = append(gopath, r)
-		imports = append(imports, r.pkgDir())
-
-		// select first GOPATH entry as default
-		if defaultRoot == nil {
-			defaultRoot = r
-		}
-	}
-
-	// use GOROOT if no valid GOPATH specified
-	if defaultRoot == nil {
-		defaultRoot = gopath[0]
-	}
-}
-
-type pkgroot struct {
-	path   string
-	goroot bool // TODO(adg): remove this once Go tree re-organized
-}
-
-func newPkgroot(p string) (*pkgroot, os.Error) {
-	if !filepath.IsAbs(p) {
-		return nil, os.NewError("must be absolute")
-	}
-	ep, err := filepath.EvalSymlinks(p)
-	if err != nil {
-		return nil, err
-	}
-	return &pkgroot{path: ep}, nil
-}
-
-func (r *pkgroot) srcDir() string {
-	if r.goroot {
-		return filepath.Join(r.path, "src", "pkg")
-	}
-	return filepath.Join(r.path, "src")
-}
-
-func (r *pkgroot) pkgDir() string {
-	goos, goarch := runtime.GOOS, runtime.GOARCH
-	if e := os.Getenv("GOOS"); e != "" {
-		goos = e
-	}
-	if e := os.Getenv("GOARCH"); e != "" {
-		goarch = e
-	}
-	return filepath.Join(r.path, "pkg", goos+"_"+goarch)
-}
-
-func (r *pkgroot) binDir() string {
-	return filepath.Join(r.path, "bin")
-}
-
-func (r *pkgroot) hasSrcDir(name string) bool {
-	fi, err := os.Stat(filepath.Join(r.srcDir(), name))
-	if err != nil {
-		return false
-	}
-	return fi.IsDirectory()
-}
-
-func (r *pkgroot) hasPkg(name string) bool {
-	fi, err := os.Stat(filepath.Join(r.pkgDir(), name+".a"))
-	if err != nil {
-		return false
-	}
-	return fi.IsRegular()
-	// TODO(adg): check object version is consistent
-}
-
-
-var ErrPackageNotFound = os.NewError("package could not be found locally")
-
-// findPackageRoot takes an import or filesystem path and returns the
-// root where the package source should be and the package import path.
-func findPackageRoot(path string) (root *pkgroot, pkg string, err os.Error) {
-	if isLocalPath(path) {
-		if path, err = filepath.Abs(path); err != nil {
-			return
-		}
-		for _, r := range gopath {
-			rpath := r.srcDir() + string(filepath.Separator)
-			if !strings.HasPrefix(path, rpath) {
-				continue
-			}
-			root = r
-			pkg = path[len(rpath):]
-			return
-		}
-		err = fmt.Errorf("path %q not inside a GOPATH", path)
-		return
-	}
-	root = defaultRoot
-	pkg = path
-	for _, r := range gopath {
-		if r.hasSrcDir(path) {
-			root = r
-			return
-		}
-	}
-	err = ErrPackageNotFound
-	return
-}
-
-// Is this a local path?  /foo ./foo ../foo . ..
-func isLocalPath(s string) bool {
-	const sep = string(filepath.Separator)
-	return strings.HasPrefix(s, sep) || strings.HasPrefix(s, "."+sep) || strings.HasPrefix(s, ".."+sep) || s == "." || s == ".."
-}
diff --git a/src/cmd/goinstall/syslist_test.go b/src/cmd/goinstall/syslist_test.go
deleted file mode 100644
index 795cd293ab..0000000000
--- a/src/cmd/goinstall/syslist_test.go
+++ /dev/null
@@ -1,61 +0,0 @@
-// Copyright 2011 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.
-package main
-
-import (
-	"runtime"
-	"testing"
-)
-
-var (
-	thisOS    = runtime.GOOS
-	thisArch  = runtime.GOARCH
-	otherOS   = anotherOS()
-	otherArch = anotherArch()
-)
-
-func anotherOS() string {
-	if thisOS != "darwin" {
-		return "darwin"
-	}
-	return "linux"
-}
-
-func anotherArch() string {
-	if thisArch != "amd64" {
-		return "amd64"
-	}
-	return "386"
-}
-
-type GoodFileTest struct {
-	name   string
-	result bool
-}
-
-var tests = []GoodFileTest{
-	{"file.go", true},
-	{"file.c", true},
-	{"file_foo.go", true},
-	{"file_" + thisArch + ".go", true},
-	{"file_" + otherArch + ".go", false},
-	{"file_" + thisOS + ".go", true},
-	{"file_" + otherOS + ".go", false},
-	{"file_" + thisOS + "_" + thisArch + ".go", true},
-	{"file_" + otherOS + "_" + thisArch + ".go", false},
-	{"file_" + thisOS + "_" + otherArch + ".go", false},
-	{"file_" + otherOS + "_" + otherArch + ".go", false},
-	{"file_foo_" + thisArch + ".go", true},
-	{"file_foo_" + otherArch + ".go", false},
-	{"file_" + thisOS + ".c", true},
-	{"file_" + otherOS + ".c", false},
-}
-
-func TestGoodOSArch(t *testing.T) {
-	for _, test := range tests {
-		if goodOSArch(test.name) != test.result {
-			t.Fatalf("goodOSArch(%q) != %v", test.name, test.result)
-		}
-	}
-}
diff --git a/src/pkg/Makefile b/src/pkg/Makefile
index c4be1da497..9bed810267 100644
--- a/src/pkg/Makefile
+++ b/src/pkg/Makefile
@@ -208,6 +208,7 @@ NOTEST+=\
 	../cmd/cgo\
 	../cmd/ebnflint\
 	../cmd/godoc\
+	../cmd/goinstall\
 	../cmd/gotest\
 	../cmd/govet\
 	../cmd/goyacc\
diff --git a/src/pkg/go/build/build.go b/src/pkg/go/build/build.go
index 3cb8efe479..8dd4c4ee44 100644
--- a/src/pkg/go/build/build.go
+++ b/src/pkg/go/build/build.go
@@ -15,8 +15,14 @@ import (
 	"strings"
 )
 
-func (d *DirInfo) Build(targ string) ([]*Cmd, os.Error) {
-	b := &build{obj: "_obj/"}
+// Build produces a build Script for the given package.
+func Build(tree *Tree, pkg string, info *DirInfo) (*Script, os.Error) {
+	s := &Script{}
+	b := &build{
+		script: s,
+		path:   filepath.Join(tree.SrcDir(), pkg),
+	}
+	b.obj = b.abs("_obj") + "/"
 
 	goarch := runtime.GOARCH
 	if g := os.Getenv("GOARCH"); g != "" {
@@ -28,17 +34,25 @@ func (d *DirInfo) Build(targ string) ([]*Cmd, os.Error) {
 		return nil, err
 	}
 
-	var gofiles = d.GoFiles // .go files to be built with gc
-	var ofiles []string     // *.GOARCH files to be linked or packed
+	// .go files to be built with gc
+	gofiles := b.abss(info.GoFiles...)
+	s.addInput(gofiles...)
+
+	var ofiles []string // object files to be linked or packed
 
 	// make build directory
 	b.mkdir(b.obj)
+	s.addIntermediate(b.obj)
 
 	// cgo
-	if len(d.CgoFiles) > 0 {
-		outGo, outObj := b.cgo(d.CgoFiles)
+	if len(info.CgoFiles) > 0 {
+		cgoFiles := b.abss(info.CgoFiles...)
+		s.addInput(cgoFiles...)
+		outGo, outObj := b.cgo(cgoFiles)
 		gofiles = append(gofiles, outGo...)
 		ofiles = append(ofiles, outObj...)
+		s.addIntermediate(outGo...)
+		s.addIntermediate(outObj...)
 	}
 
 	// compile
@@ -46,31 +60,130 @@ func (d *DirInfo) Build(targ string) ([]*Cmd, os.Error) {
 		ofile := b.obj + "_go_." + b.arch
 		b.gc(ofile, gofiles...)
 		ofiles = append(ofiles, ofile)
+		s.addIntermediate(ofile)
 	}
 
 	// assemble
-	for _, sfile := range d.SFiles {
+	for _, sfile := range info.SFiles {
 		ofile := b.obj + sfile[:len(sfile)-1] + b.arch
+		sfile = b.abs(sfile)
+		s.addInput(sfile)
 		b.asm(ofile, sfile)
 		ofiles = append(ofiles, ofile)
+		s.addIntermediate(sfile, ofile)
 	}
 
 	if len(ofiles) == 0 {
 		return nil, os.NewError("make: no object files to build")
 	}
 
-	if d.IsCommand() {
+	// choose target file
+	var targ string
+	if info.IsCommand() {
+		// use the last part of the import path as binary name
+		_, bin := filepath.Split(pkg)
+		targ = filepath.Join(tree.BinDir(), bin)
+	} else {
+		targ = filepath.Join(tree.PkgDir(), pkg+".a")
+	}
+
+	// make target directory
+	targDir, _ := filepath.Split(targ)
+	b.mkdir(targDir)
+
+	// link binary or pack object
+	if info.IsCommand() {
 		b.ld(targ, ofiles...)
 	} else {
 		b.gopack(targ, ofiles...)
 	}
+	s.Output = append(s.Output, targ)
+
+	return b.script, nil
+}
+
+// A Script describes the build process for a Go package.
+// The Input, Intermediate, and Output fields are lists of absolute paths.
+type Script struct {
+	Cmd          []*Cmd
+	Input        []string
+	Intermediate []string
+	Output       []string
+}
+
+func (s *Script) addInput(file ...string) {
+	s.Input = append(s.Input, file...)
+}
+
+func (s *Script) addIntermediate(file ...string) {
+	s.Intermediate = append(s.Intermediate, file...)
+}
+
+// Run runs the Script's Cmds in order.
+func (s *Script) Run() os.Error {
+	for _, c := range s.Cmd {
+		if err := c.Run(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
 
-	return b.cmds, nil
+// Stale returns true if the build's inputs are newer than its outputs.
+func (s *Script) Stale() bool {
+	var latest int64
+	// get latest mtime of outputs
+	for _, file := range s.Output {
+		fi, err := os.Stat(file)
+		if err != nil {
+			// any error reading output files means stale
+			return true
+		}
+		if m := fi.Mtime_ns; m > latest {
+			latest = m
+		}
+	}
+	for _, file := range s.Input {
+		fi, err := os.Stat(file)
+		if err != nil || fi.Mtime_ns > latest {
+			// any error reading input files means stale
+			// (attempt to rebuild to figure out why)
+			return true
+		}
+	}
+	return false
 }
 
+// Clean removes the Script's Intermediate files.
+// It tries to remove every file and returns the first error it encounters.
+func (s *Script) Clean() (err os.Error) {
+	for i := len(s.Intermediate) - 1; i >= 0; i-- {
+		if e := os.Remove(s.Intermediate[i]); err == nil {
+			err = e
+		}
+	}
+	return
+}
+
+// Clean removes the Script's Intermediate and Output files.
+// It tries to remove every file and returns the first error it encounters.
+func (s *Script) Nuke() (err os.Error) {
+	for i := len(s.Output) - 1; i >= 0; i-- {
+		if e := os.Remove(s.Output[i]); err == nil {
+			err = e
+		}
+	}
+	if e := s.Clean(); err == nil {
+		err = e
+	}
+	return
+}
+
+// A Cmd describes an individual build command.
 type Cmd struct {
 	Args   []string // command-line
 	Stdout string   // write standard output to this file, "" is passthrough
+	Dir    string   // working directory
 	Input  []string // file paths (dependencies)
 	Output []string // file paths
 }
@@ -79,14 +192,15 @@ func (c *Cmd) String() string {
 	return strings.Join(c.Args, " ")
 }
 
-func (c *Cmd) Run(dir string) os.Error {
+// Run executes the Cmd.
+func (c *Cmd) Run() os.Error {
 	out := new(bytes.Buffer)
 	cmd := exec.Command(c.Args[0], c.Args[1:]...)
-	cmd.Dir = dir
+	cmd.Dir = c.Dir
 	cmd.Stdout = out
 	cmd.Stderr = out
 	if c.Stdout != "" {
-		f, err := os.Create(filepath.Join(dir, c.Stdout))
+		f, err := os.Create(c.Stdout)
 		if err != nil {
 			return err
 		}
@@ -99,15 +213,6 @@ func (c *Cmd) Run(dir string) os.Error {
 	return nil
 }
 
-func (c *Cmd) Clean(dir string) (err os.Error) {
-	for _, fn := range c.Output {
-		if e := os.RemoveAll(fn); err == nil {
-			err = e
-		}
-	}
-	return
-}
-
 // ArchChar returns the architecture character for the given goarch.
 // For example, ArchChar("amd64") returns "6".
 func ArchChar(goarch string) (string, os.Error) {
@@ -123,13 +228,29 @@ func ArchChar(goarch string) (string, os.Error) {
 }
 
 type build struct {
-	cmds []*Cmd
-	obj  string
-	arch string
+	script *Script
+	path   string
+	obj    string
+	arch   string
+}
+
+func (b *build) abs(file string) string {
+	if filepath.IsAbs(file) {
+		return file
+	}
+	return filepath.Join(b.path, file)
+}
+
+func (b *build) abss(file ...string) []string {
+	s := make([]string, len(file))
+	for i, f := range file {
+		s[i] = b.abs(f)
+	}
+	return s
 }
 
 func (b *build) add(c Cmd) {
-	b.cmds = append(b.cmds, &c)
+	b.script.Cmd = append(b.script.Cmd, &c)
 }
 
 func (b *build) mkdir(name string) {
@@ -222,6 +343,7 @@ func (b *build) cgo(cgofiles []string) (outGo, outObj []string) {
 	gofiles := []string{b.obj + "_cgo_gotypes.go"}
 	cfiles := []string{b.obj + "_cgo_main.c", b.obj + "_cgo_export.c"}
 	for _, fn := range cgofiles {
+		fn = filepath.Base(fn)
 		f := b.obj + fn[:len(fn)-2]
 		gofiles = append(gofiles, f+"cgo1.go")
 		cfiles = append(cfiles, f+"cgo2.c")
diff --git a/src/pkg/go/build/build_test.go b/src/pkg/go/build/build_test.go
index c543eddbda..c760c5cc6f 100644
--- a/src/pkg/go/build/build_test.go
+++ b/src/pkg/go/build/build_test.go
@@ -5,50 +5,46 @@
 package build
 
 import (
-	"os"
 	"path/filepath"
 	"runtime"
 	"strings"
 	"testing"
 )
 
-var buildDirs = []string{
-	"pkg/path",
-	"cmd/gofix",
-	"pkg/big",
-	"pkg/go/build/cgotest",
+// TODO(adg): test building binaries
+
+var buildPkgs = []string{
+	"path",
+	"big",
+	"go/build/cgotest",
 }
 
 func TestBuild(t *testing.T) {
-	out, err := filepath.Abs("_test/out")
-	if err != nil {
-		t.Fatal(err)
-	}
-	for _, d := range buildDirs {
-		if runtime.GOARCH == "arm" && strings.Contains(d, "/cgo") {
+	for _, pkg := range buildPkgs {
+		if runtime.GOARCH == "arm" && strings.Contains(pkg, "/cgo") {
 			// no cgo for arm, yet.
 			continue
 		}
-		dir := filepath.Join(runtime.GOROOT(), "src", d)
-		testBuild(t, dir, out)
+		tree := Path[0] // Goroot
+		testBuild(t, tree, pkg)
 	}
 }
 
-func testBuild(t *testing.T, dir, targ string) {
-	d, err := ScanDir(dir, true)
+func testBuild(t *testing.T, tree *Tree, pkg string) {
+	dir := filepath.Join(tree.SrcDir(), pkg)
+	info, err := ScanDir(dir, true)
 	if err != nil {
 		t.Error(err)
 		return
 	}
-	defer os.Remove(targ)
-	cmds, err := d.Build(targ)
+	s, err := Build(tree, pkg, info)
 	if err != nil {
 		t.Error(err)
 		return
 	}
-	for _, c := range cmds {
+	for _, c := range s.Cmd {
 		t.Log("Run:", c)
-		err = c.Run(dir)
+		err = c.Run()
 		if err != nil {
 			t.Error(c, err)
 			return
diff --git a/src/pkg/go/build/dir.go b/src/pkg/go/build/dir.go
index 77e80bff0b..dda33bb6b6 100644
--- a/src/pkg/go/build/dir.go
+++ b/src/pkg/go/build/dir.go
@@ -50,7 +50,6 @@ func ScanDir(dir string, allowMain bool) (info *DirInfo, err os.Error) {
 
 	var di DirInfo
 	imported := make(map[string]bool)
-	pkgName := ""
 	fset := token.NewFileSet()
 	for i := range dirs {
 		d := &dirs[i]
@@ -89,14 +88,14 @@ func ScanDir(dir string, allowMain bool) (info *DirInfo, err os.Error) {
 		if s == "documentation" {
 			continue
 		}
-		if pkgName == "" {
-			pkgName = s
-		} else if pkgName != s {
+		if di.PkgName == "" {
+			di.PkgName = s
+		} else if di.PkgName != s {
 			// Only if all files in the directory are in package main
-			// do we return pkgName=="main".
+			// do we return PkgName=="main".
 			// A mix of main and another package reverts
 			// to the original (allowMain=false) behaviour.
-			if s == "main" || pkgName == "main" {
+			if s == "main" || di.PkgName == "main" {
 				return ScanDir(dir, false)
 			}
 			return nil, os.ErrorString("multiple package names in " + dir)