cmd/gomobile: use nm to build list of packages

Today we only look at direct imports of package main for an import of
golang.org/x/mobile/app, which is unfortunate. We also do a complete
package tree load using go/build looking for the OpenAL import when
building for android, which involves reading a lot of files.

The compiler and linker have already done all of this work for us.
Run nm on the output binary and extract package names from it.

Change-Id: Ie4f07befede5017bbca7d24325062369d4b5c30d
Reviewed-on: https://go-review.googlesource.com/12645
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

cmd/gomobile/build.go

@@ -7,11 +7,13 @@
 package main
 
 import (
+	"bufio"
 	"fmt"
 	"go/build"
 	"io"
 	"os"
 	"os/exec"
+	"regexp"
 	"runtime"
 	"strconv"
 	"strings"
@@ -90,12 +92,14 @@ func runBuild(cmd *command) (err error) {
 		return fmt.Errorf("cannot set -o when building non-main package")
 	}
 
+	var nmpkgs map[string]bool
 	switch buildTarget {
 	case "android":
 		if pkg.Name != "main" {
 			return goBuild(pkg.ImportPath, androidArmEnv)
 		}
-		if err := goAndroidBuild(pkg); err != nil {
+		nmpkgs, err = goAndroidBuild(pkg)
+		if err != nil {
 			return err
 		}
 	case "ios":
@@ -108,22 +112,53 @@ func runBuild(cmd *command) (err error) {
 			}
 			return goBuild(pkg.ImportPath, darwinArm64Env)
 		}
-		if err := goIOSBuild(pkg); err != nil {
+		nmpkgs, err = goIOSBuild(pkg)
+		if err != nil {
 			return err
 		}
 	}
 
-	// TODO(crawshaw): This is an incomplete package scan.
-	// A complete package scan would be too expensive. Instead,
-	// fake it. After the binary is built, scan its symbols
-	// with nm and look for the app and al packages.
-	if err := importsApp(pkg); err != nil {
-		return err
+	if !nmpkgs["golang.org/x/mobile/app"] {
+		return fmt.Errorf(`%s does not import "golang.org/x/mobile/app"`, pkg.ImportPath)
 	}
 
 	return nil
 }
 
+var nmRE = regexp.MustCompile(`[0-9a-f]{8} t (golang.org/x.*/[^.]*)`)
+
+func extractPkgs(nm string, path string) (map[string]bool, error) {
+	if buildN {
+		return map[string]bool{"golang.org/x/mobile/app": true}, nil
+	}
+	r, w := io.Pipe()
+	cmd := exec.Command(nm, path)
+	cmd.Stdout = w
+	cmd.Stderr = os.Stderr
+
+	nmpkgs := make(map[string]bool)
+	errc := make(chan error, 1)
+	go func() {
+		s := bufio.NewScanner(r)
+		for s.Scan() {
+			if res := nmRE.FindStringSubmatch(s.Text()); res != nil {
+				nmpkgs[res[1]] = true
+			}
+		}
+		errc <- s.Err()
+	}()
+
+	err := cmd.Run()
+	w.Close()
+	if err != nil {
+		return nil, fmt.Errorf("%s %s: %v", nm, path, err)
+	}
+	if err := <-errc; err != nil {
+		return nil, fmt.Errorf("%s %s: %v", nm, path, err)
+	}
+	return nmpkgs, nil
+}
+
 func importsApp(pkg *build.Package) error {
 	// Building a program, make sure it is appropriate for mobile.
 	for _, path := range pkg.Imports {

cmd/gomobile/build_androidapp.go

@@ -21,12 +21,12 @@ import (
 	"strings"
 )
 
-func goAndroidBuild(pkg *build.Package) error {
+func goAndroidBuild(pkg *build.Package) (map[string]bool, error) {
 	libName := path.Base(pkg.ImportPath)
 	manifestData, err := ioutil.ReadFile(filepath.Join(pkg.Dir, "AndroidManifest.xml"))
 	if err != nil {
 		if !os.IsNotExist(err) {
-			return err
+			return nil, err
 		}
 		buf := new(bytes.Buffer)
 		buf.WriteString(`<?xml version="1.0" encoding="utf-8"?>`)
@@ -37,7 +37,7 @@ func goAndroidBuild(pkg *build.Package) error {
 			LibName:     libName,
 		})
 		if err != nil {
-			return err
+			return nil, err
 		}
 		manifestData = buf.Bytes()
 		if buildV {
@@ -46,7 +46,7 @@ func goAndroidBuild(pkg *build.Package) error {
 	} else {
 		libName, err = manifestLibName(manifestData)
 		if err != nil {
-			return err
+			return nil, err
 		}
 	}
 	libPath := filepath.Join(tmpdir, "lib"+libName+".so")
@@ -58,28 +58,34 @@ func goAndroidBuild(pkg *build.Package) error {
 		"-o", libPath,
 	)
 	if err != nil {
-		return err
+		return nil, err
 	}
+
+	nmpkgs, err := extractPkgs(androidArmNM, libPath)
+	if err != nil {
+		return nil, err
+	}
+
 	block, _ := pem.Decode([]byte(debugCert))
 	if block == nil {
-		return errors.New("no debug cert")
+		return nil, errors.New("no debug cert")
 	}
 	privKey, err := x509.ParsePKCS1PrivateKey(block.Bytes)
 	if err != nil {
-		return err
+		return nil, err
 	}
 
 	if buildO == "" {
 		buildO = filepath.Base(pkg.Dir) + ".apk"
 	}
 	if !strings.HasSuffix(buildO, ".apk") {
-		return fmt.Errorf("output file name %q does not end in '.apk'", buildO)
+		return nil, fmt.Errorf("output file name %q does not end in '.apk'", buildO)
 	}
 	var out io.Writer
 	if !buildN {
 		f, err := os.Create(buildO)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		defer func() {
 			if cerr := f.Close(); err == nil {
@@ -105,39 +111,39 @@ func goAndroidBuild(pkg *build.Package) error {
 
 	w, err := apkwcreate("AndroidManifest.xml")
 	if err != nil {
-		return err
+		return nil, err
 	}
 	if _, err := w.Write(manifestData); err != nil {
-		return err
+		return nil, err
 	}
 
 	w, err = apkwcreate("classes.dex")
 	if err != nil {
-		return err
+		return nil, err
 	}
 	dexData, err := base64.StdEncoding.DecodeString(dexStr)
 	if err != nil {
 		log.Fatal("internal error bad dexStr: %v", err)
 	}
 	if _, err := w.Write(dexData); err != nil {
-		return err
+		return nil, err
 	}
 
 	w, err = apkwcreate("lib/armeabi/lib" + libName + ".so")
 	if err != nil {
-		return err
+		return nil, err
 	}
 	if !buildN {
 		r, err := os.Open(libPath)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		if _, err := io.Copy(w, r); err != nil {
-			return err
+			return nil, err
 		}
 	}
 
-	if pkgImportsAL(pkg) {
+	if nmpkgs["golang.org/x/mobile/exp/audio/al"] {
 		alDir := filepath.Join(ndkccpath, "openal/lib")
 		filepath.Walk(alDir, func(path string, info os.FileInfo, err error) error {
 			if err != nil {
@@ -171,7 +177,7 @@ func goAndroidBuild(pkg *build.Package) error {
 		if os.IsNotExist(err) {
 			assetsDirExists = false
 		} else {
-			return err
+			return nil, err
 		}
 	} else {
 		assetsDirExists = fi.IsDir()
@@ -198,7 +204,7 @@ func goAndroidBuild(pkg *build.Package) error {
 			return err
 		})
 		if err != nil {
-			return fmt.Errorf("asset %v", err)
+			return nil, fmt.Errorf("asset %v", err)
 		}
 	}
 
@@ -206,39 +212,11 @@ func goAndroidBuild(pkg *build.Package) error {
 
 	if !buildN {
 		if err := apkw.Close(); err != nil {
-			return err
+			return nil, err
 		}
 	}
 
-	return nil
-}
-
-var importsALPkg = make(map[string]struct{})
-
-// pkgImportsAL returns true if the given package or one of its
-// dependencies imports the x/mobile/exp/audio/al package.
-func pkgImportsAL(pkg *build.Package) bool {
-	for _, path := range pkg.Imports {
-		if path == "C" {
-			continue
-		}
-		if _, ok := importsALPkg[path]; ok {
-			continue
-		}
-		importsALPkg[path] = struct{}{}
-		if strings.HasPrefix(path, "golang.org/x/mobile/exp/audio/al") {
-			return true
-		}
-		dPkg, err := ctx.Import(path, "", build.ImportComment)
-		if err != nil {
-			fmt.Fprintf(os.Stderr, "error reading OpenAL library: %v", err)
-			os.Exit(2)
-		}
-		if pkgImportsAL(dPkg) {
-			return true
-		}
-	}
-	return false
+	return nmpkgs, nil
 }
 
 // A random uninteresting private key.

cmd/gomobile/build_iosapp.go

@@ -17,17 +17,17 @@ import (
 	"text/template"
 )
 
-func goIOSBuild(pkg *build.Package) error {
+func goIOSBuild(pkg *build.Package) (map[string]bool, error) {
 	src := pkg.ImportPath
 	if buildO != "" && !strings.HasSuffix(buildO, ".app") {
-		return fmt.Errorf("-o must have an .app for target=ios")
+		return nil, fmt.Errorf("-o must have an .app for target=ios")
 	}
 
 	infoplist := new(bytes.Buffer)
 	if err := infoplistTmpl.Execute(infoplist, manifestTmplData{
 		Name: strings.Title(path.Base(pkg.ImportPath)),
 	}); err != nil {
-		return err
+		return nil, err
 	}
 
 	files := []struct {
@@ -41,26 +41,30 @@ func goIOSBuild(pkg *build.Package) error {
 
 	for _, file := range files {
 		if err := mkdir(filepath.Dir(file.name)); err != nil {
-			return err
+			return nil, err
 		}
 		if buildX {
 			printcmd("echo \"%s\" > %s", file.contents, file.name)
 		}
 		if !buildN {
 			if err := ioutil.WriteFile(file.name, file.contents, 0644); err != nil {
-				return err
+				return nil, err
 			}
 		}
 	}
 
 	armPath := filepath.Join(tmpdir, "arm")
 	if err := goBuild(src, darwinArmEnv, "-tags=ios", "-o="+armPath); err != nil {
-		return err
+		return nil, err
+	}
+	nmpkgs, err := extractPkgs(darwinArmNM, armPath)
+	if err != nil {
+		return nil, err
 	}
 
 	arm64Path := filepath.Join(tmpdir, "arm64")
 	if err := goBuild(src, darwinArm64Env, "-tags=ios", "-o="+arm64Path); err != nil {
-		return err
+		return nil, err
 	}
 
 	// Apple requires builds to target both darwin/arm and darwin/arm64.
@@ -73,12 +77,12 @@ func goIOSBuild(pkg *build.Package) error {
 		"-o", filepath.Join(tmpdir, "main/main"),
 	)
 	if err := runCmd(cmd); err != nil {
-		return err
+		return nil, err
 	}
 
 	// TODO(jbd): Set the launcher icon.
 	if err := iosCopyAssets(pkg, tmpdir); err != nil {
-		return err
+		return nil, err
 	}
 
 	// Build and move the release build to the output directory.
@@ -88,7 +92,7 @@ func goIOSBuild(pkg *build.Package) error {
 		"-project", tmpdir+"/main.xcodeproj",
 	)
 	if err := runCmd(cmd); err != nil {
-		return err
+		return nil, err
 	}
 
 	// TODO(jbd): Fallback to copying if renaming fails.
@@ -101,13 +105,13 @@ func goIOSBuild(pkg *build.Package) error {
 	if !buildN {
 		// if output already exists, remove.
 		if err := os.RemoveAll(buildO); err != nil {
-			return err
+			return nil, err
 		}
 		if err := os.Rename(tmpdir+"/build/Release-iphoneos/main.app", buildO); err != nil {
-			return err
+			return nil, err
 		}
 	}
-	return nil
+	return nmpkgs, nil
 }
 
 func iosCopyAssets(pkg *build.Package, xcodeProjDir string) error {

cmd/gomobile/env.go

@@ -23,6 +23,9 @@ var (
 	darwinArm64Env []string
 	darwin386Env   []string
 	darwinAmd64Env []string
+
+	androidArmNM string
+	darwinArmNM  string
 )
 
 func buildEnvInit() (cleanup func(), err error) {
@@ -104,6 +107,7 @@ func envInit() (err error) {
 		"CXX=" + filepath.Join(ndkccbin, "arm-linux-androideabi-g++"+exe),
 		"CGO_ENABLED=1",
 	}
+	androidArmNM = filepath.Join(ndkccbin, "arm-linux-androideabi-nm"+exe)
 
 	if runtime.GOOS != "darwin" {
 		return nil
@@ -123,6 +127,7 @@ func envInit() (err error) {
 		"CGO_LDFLAGS=" + cflags + " -arch " + archClang("arm"),
 		"CGO_ENABLED=1",
 	}
+	darwinArmNM = "nm"
 	darwinArm64Env = []string{
 		"GOOS=darwin",
 		"GOARCH=arm64",

cmd/gomobile/init.go

@@ -430,7 +430,6 @@ func fetchFullNDK() error {
 	}
 	inflate.Dir = tmpdir
 	return runCmd(inflate)
-	return nil
 }
 
 // fetch reads a URL into $GOPATH/pkg/gomobile/dl and returns the path