cmd/gomobile/env.go - mobile - Git at Google

 package main

 import (
 	"bufio"
 	"encoding/json"
 	"errors"
 	"fmt"
 	"io/fs"
 	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"

 	"golang.org/x/mobile/internal/sdkpath"
 )

 // General mobile build environment. Initialized by envInit.
 var (
 	gomobilepath string              // $GOPATH/pkg/gomobile
 	androidEnv   map[string][]string // android arch -> []string
 	appleEnv     map[string][]string
 	appleNM      string
 )

 func isAndroidPlatform(platform string) bool {
 	return platform == "android"
 }

 func isApplePlatform(platform string) bool {
 	return contains(applePlatforms, platform)
 }

 var applePlatforms = []string{"ios", "iossimulator", "macos", "maccatalyst"}

 func platformArchs(platform string) []string {
 	switch platform {
 	case "ios":
 		return []string{"arm64"}
 	case "iossimulator":
 		return []string{"arm64", "amd64"}
 	case "macos", "maccatalyst":
 		return []string{"arm64", "amd64"}
 	case "android":
 		return []string{"arm", "arm64", "386", "amd64"}
 	default:
 		panic(fmt.Sprintf("unexpected platform: %s", platform))
 	}
 }

 func isSupportedArch(platform, arch string) bool {
 	return contains(platformArchs(platform), arch)
 }

 // platformOS returns the correct GOOS value for platform.
 func platformOS(platform string) string {
 	switch platform {
 	case "android":
 		return "android"
 	case "ios", "iossimulator":
 		return "ios"
 	case "macos", "maccatalyst":
 		// For "maccatalyst", Go packages should be built with GOOS=darwin,
 		// not GOOS=ios, since the underlying OS (and kernel, runtime) is macOS.
 		// We also apply a "macos" or "maccatalyst" build tag, respectively.
 		// See below for additional context.
 		return "darwin"
 	default:
 		panic(fmt.Sprintf("unexpected platform: %s", platform))
 	}
 }

 func platformTags(platform string) []string {
 	switch platform {
 	case "android":
 		return []string{"android"}
 	case "ios", "iossimulator":
 		return []string{"ios"}
 	case "macos":
 		return []string{"macos"}
 	case "maccatalyst":
 		// Mac Catalyst is a subset of iOS APIs made available on macOS
 		// designed to ease porting apps developed for iPad to macOS.
 		// See https://developer.apple.com/mac-catalyst/.
 		// Because of this, when building a Go package targeting maccatalyst,
 		// GOOS=darwin (not ios). To bridge the gap and enable maccatalyst
 		// packages to be compiled, we also specify the "ios" build tag.
 		// To help discriminate between darwin, ios, macos, and maccatalyst
 		// targets, there is also a "maccatalyst" tag.
 		// Some additional context on this can be found here:
 		// https://stackoverflow.com/questions/12132933/preprocessor-macro-for-os-x-targets/49560690#49560690
 		// TODO(ydnar): remove tag "ios" when cgo supports Catalyst
 		// See golang.org/issues/47228
 		return []string{"ios", "macos", "maccatalyst"}
 	default:
 		panic(fmt.Sprintf("unexpected platform: %s", platform))
 	}
 }

 func contains(haystack []string, needle string) bool {
 	for _, v := range haystack {
 		if v == needle {
 			return true
 		}
 	}
 	return false
 }

 func buildEnvInit() (cleanup func(), err error) {
 	// Find gomobilepath.
 	gopath := goEnv("GOPATH")
 	for _, p := range filepath.SplitList(gopath) {
 		gomobilepath = filepath.Join(p, "pkg", "gomobile")
 		if _, err := os.Stat(gomobilepath); buildN || err == nil {
 			break
 		}
 	}

 	if buildX {
 		fmt.Fprintln(xout, "GOMOBILE="+gomobilepath)
 	}

 	// Check the toolchain is in a good state.
 	// Pick a temporary directory for assembling an apk/app.
 	if gomobilepath == "" {
 		return nil, errors.New("toolchain not installed, run `gomobile init`")
 	}

 	cleanupFn := func() {
 		if buildWork {
 			fmt.Printf("WORK=%s\n", tmpdir)
 			return
 		}
 		removeAll(tmpdir)
 	}
 	if buildN {
 		tmpdir = "$WORK"
 		cleanupFn = func() {}
 	} else {
 		tmpdir, err = ioutil.TempDir("", "gomobile-work-")
 		if err != nil {
 			return nil, err
 		}
 	}
 	if buildX {
 		fmt.Fprintln(xout, "WORK="+tmpdir)
 	}

 	if err := envInit(); err != nil {
 		return nil, err
 	}

 	return cleanupFn, nil
 }

 func envInit() (err error) {
 	// Setup the cross-compiler environments.
 	if ndkRoot, err := ndkRoot(); err == nil {
 		androidEnv = make(map[string][]string)
 		if buildAndroidAPI < minAndroidAPI {
 			return fmt.Errorf("gomobile requires Android API level >= %d", minAndroidAPI)
 		}
 		for arch, toolchain := range ndk {
 			clang := toolchain.Path(ndkRoot, "clang")
 			clangpp := toolchain.Path(ndkRoot, "clang++")
 			if !buildN {
 				tools := []string{clang, clangpp}
 				if runtime.GOOS == "windows" {
 					// Because of https://github.com/android-ndk/ndk/issues/920,
 					// we require r19c, not just r19b. Fortunately, the clang++.cmd
 					// script only exists in r19c.
 					tools = append(tools, clangpp+".cmd")
 				}
 				for _, tool := range tools {
 					_, err = os.Stat(tool)
 					if err != nil {
 						return fmt.Errorf("No compiler for %s was found in the NDK (tried %s). Make sure your NDK version is >= r19c. Use `sdkmanager --update` to update it.", arch, tool)
 					}
 				}
 			}
 			androidEnv[arch] = []string{
 				"GOOS=android",
 				"GOARCH=" + arch,
 				"CC=" + clang,
 				"CXX=" + clangpp,
 				"CGO_ENABLED=1",
 			}
 			if arch == "arm" {
 				androidEnv[arch] = append(androidEnv[arch], "GOARM=7")
 			}
 		}
 	}

 	if !xcodeAvailable() {
 		return nil
 	}

 	appleNM = "nm"
 	appleEnv = make(map[string][]string)
 	for _, platform := range applePlatforms {
 		for _, arch := range platformArchs(platform) {
 			var env []string
 			var goos, sdk, clang, cflags string
 			var err error
 			switch platform {
 			case "ios":
 				goos = "ios"
 				sdk = "iphoneos"
 				clang, cflags, err = envClang(sdk)
 				cflags += " -miphoneos-version-min=" + buildIOSVersion
 				cflags += " -fembed-bitcode"
 			case "iossimulator":
 				goos = "ios"
 				sdk = "iphonesimulator"
 				clang, cflags, err = envClang(sdk)
 				cflags += " -mios-simulator-version-min=" + buildIOSVersion
 				cflags += " -fembed-bitcode"
 			case "maccatalyst":
 				// Mac Catalyst is a subset of iOS APIs made available on macOS
 				// designed to ease porting apps developed for iPad to macOS.
 				// See https://developer.apple.com/mac-catalyst/.
 				// Because of this, when building a Go package targeting maccatalyst,
 				// GOOS=darwin (not ios). To bridge the gap and enable maccatalyst
 				// packages to be compiled, we also specify the "ios" build tag.
 				// To help discriminate between darwin, ios, macos, and maccatalyst
 				// targets, there is also a "maccatalyst" tag.
 				// Some additional context on this can be found here:
 				// https://stackoverflow.com/questions/12132933/preprocessor-macro-for-os-x-targets/49560690#49560690
 				goos = "darwin"
 				sdk = "macosx"
 				clang, cflags, err = envClang(sdk)
 				// TODO(ydnar): the following 3 lines MAY be needed to compile
 				// packages or apps for maccatalyst. Commenting them out now in case
 				// it turns out they are necessary. Currently none of the example
 				// apps will build for macos or maccatalyst because they have a
 				// GLKit dependency, which is deprecated on all Apple platforms, and
 				// broken on maccatalyst (GLKView isn’t available).
 				// sysroot := strings.SplitN(cflags, " ", 2)[1]
 				// cflags += " -isystem " + sysroot + "/System/iOSSupport/usr/include"
 				// cflags += " -iframework " + sysroot + "/System/iOSSupport/System/Library/Frameworks"
 				switch arch {
 				case "amd64":
 					cflags += " -target x86_64-apple-ios" + buildIOSVersion + "-macabi"
 				case "arm64":
 					cflags += " -target arm64-apple-ios" + buildIOSVersion + "-macabi"
 					cflags += " -fembed-bitcode"
 				}
 			case "macos":
 				goos = "darwin"
 				sdk = "macosx" // Note: the SDK is called "macosx", not "macos"
 				clang, cflags, err = envClang(sdk)
 				if arch == "arm64" {
 					cflags += " -fembed-bitcode"
 				}
 			default:
 				panic(fmt.Errorf("unknown Apple target: %s/%s", platform, arch))
 			}

 			if err != nil {
 				return err
 			}

 			env = append(env,
 				"GOOS="+goos,
 				"GOARCH="+arch,
 				"GOFLAGS="+"-tags="+strings.Join(platformTags(platform), ","),
 				"CC="+clang,
 				"CXX="+clang+"++",
 				"CGO_CFLAGS="+cflags+" -arch "+archClang(arch),
 				"CGO_CXXFLAGS="+cflags+" -arch "+archClang(arch),
 				"CGO_LDFLAGS="+cflags+" -arch "+archClang(arch),
 				"CGO_ENABLED=1",
 				"DARWIN_SDK="+sdk,
 			)
 			appleEnv[platform+"/"+arch] = env
 		}
 	}

 	return nil
 }

 // abi maps GOARCH values to Android ABI strings.
 // See https://developer.android.com/ndk/guides/abis
 func abi(goarch string) string {
 	switch goarch {
 	case "arm":
 		return "armeabi-v7a"
 	case "arm64":
 		return "arm64-v8a"
 	case "386":
 		return "x86"
 	case "amd64":
 		return "x86_64"
 	default:
 		return ""
 	}
 }

 // checkNDKRoot returns nil if the NDK in `ndkRoot` supports the current configured
 // API version and all the specified Android targets.
 func checkNDKRoot(ndkRoot string, targets []targetInfo) error {
 	platformsJson, err := os.Open(filepath.Join(ndkRoot, "meta", "platforms.json"))
 	if err != nil {
 		return err
 	}
 	defer platformsJson.Close()
 	decoder := json.NewDecoder(platformsJson)
 	supportedVersions := struct {
 		Min int
 		Max int
 	}{}
 	if err := decoder.Decode(&supportedVersions); err != nil {
 		return err
 	}
 	if supportedVersions.Min > buildAndroidAPI ||
 		supportedVersions.Max < buildAndroidAPI {
 		return fmt.Errorf("unsupported API version %d (not in %d..%d)", buildAndroidAPI, supportedVersions.Min, supportedVersions.Max)
 	}
 	abisJson, err := os.Open(filepath.Join(ndkRoot, "meta", "abis.json"))
 	if err != nil {
 		return err
 	}
 	defer abisJson.Close()
 	decoder = json.NewDecoder(abisJson)
 	abis := make(map[string]struct{})
 	if err := decoder.Decode(&abis); err != nil {
 		return err
 	}
 	for _, target := range targets {
 		if !isAndroidPlatform(target.platform) {
 			continue
 		}
 		if _, found := abis[abi(target.arch)]; !found {
 			return fmt.Errorf("ndk does not support %s", target.platform)
 		}
 	}
 	return nil
 }

 // compatibleNDKRoots searches the side-by-side NDK dirs for compatible SDKs.
 func compatibleNDKRoots(ndkForest string, targets []targetInfo) ([]string, error) {
 	ndkDirs, err := ioutil.ReadDir(ndkForest)
 	if err != nil {
 		return nil, err
 	}
 	compatibleNDKRoots := []string{}
 	var lastErr error
 	for _, dirent := range ndkDirs {
 		ndkRoot := filepath.Join(ndkForest, dirent.Name())
 		lastErr = checkNDKRoot(ndkRoot, targets)
 		if lastErr == nil {
 			compatibleNDKRoots = append(compatibleNDKRoots, ndkRoot)
 		}
 	}
 	if len(compatibleNDKRoots) > 0 {
 		return compatibleNDKRoots, nil
 	}
 	return nil, lastErr
 }

 // ndkVersion returns the full version number of an installed copy of the NDK,
 // or "" if it cannot be determined.
 func ndkVersion(ndkRoot string) string {
 	properties, err := os.Open(filepath.Join(ndkRoot, "source.properties"))
 	if err != nil {
 		return ""
 	}
 	defer properties.Close()
 	// Parse the version number out of the .properties file.
 	// See https://en.wikipedia.org/wiki/.properties
 	scanner := bufio.NewScanner(properties)
 	for scanner.Scan() {
 		line := scanner.Text()
 		tokens := strings.SplitN(line, "=", 2)
 		if len(tokens) != 2 {
 			continue
 		}
 		if strings.TrimSpace(tokens[0]) == "Pkg.Revision" {
 			return strings.TrimSpace(tokens[1])
 		}
 	}
 	return ""
 }

 // ndkRoot returns the root path of an installed NDK that supports all the
 // specified Android targets. For details of NDK locations, see
 // https://github.com/android/ndk-samples/wiki/Configure-NDK-Path
 func ndkRoot(targets ...targetInfo) (string, error) {
 	if buildN {
 		return "$NDK_PATH", nil
 	}

 	// Try the ANDROID_NDK_HOME variable.  This approach is deprecated, but it
 	// has the highest priority because it represents an explicit user choice.
 	if ndkRoot := os.Getenv("ANDROID_NDK_HOME"); ndkRoot != "" {
 		if err := checkNDKRoot(ndkRoot, targets); err != nil {
 			return "", fmt.Errorf("ANDROID_NDK_HOME specifies %s, which is unusable: %w", ndkRoot, err)
 		}
 		return ndkRoot, nil
 	}

 	androidHome, err := sdkpath.AndroidHome()
 	if err != nil {
 		return "", fmt.Errorf("could not locate Android SDK: %w", err)
 	}

 	// Use the newest compatible NDK under the side-by-side path arrangement.
 	ndkForest := filepath.Join(androidHome, "ndk")
 	ndkRoots, sideBySideErr := compatibleNDKRoots(ndkForest, targets)
 	if len(ndkRoots) != 0 {
 		// Choose the latest version that supports the build configuration.
 		// NDKs whose version cannot be determined will be least preferred.
 		// In the event of a tie, the later ndkRoot will win.
 		maxVersion := ""
 		var selected string
 		for _, ndkRoot := range ndkRoots {
 			version := ndkVersion(ndkRoot)
 			if version >= maxVersion {
 				maxVersion = version
 				selected = ndkRoot
 			}
 		}
 		return selected, nil
 	}
 	// Try the deprecated NDK location.
 	ndkRoot := filepath.Join(androidHome, "ndk-bundle")
 	if legacyErr := checkNDKRoot(ndkRoot, targets); legacyErr != nil {
 		return "", fmt.Errorf("no usable NDK in %s: %w, %v", androidHome, sideBySideErr, legacyErr)
 	}
 	return ndkRoot, nil
 }

 func envClang(sdkName string) (clang, cflags string, err error) {
 	if buildN {
 		return sdkName + "-clang", "-isysroot " + sdkName, nil
 	}
 	cmd := exec.Command("xcrun", "--sdk", sdkName, "--find", "clang")
 	out, err := cmd.Output()
 	if err != nil {
 		if ee := (*exec.ExitError)(nil); errors.As(err, &ee) {
 			out = append(out, ee.Stderr...)
 		}
 		return "", "", fmt.Errorf("xcrun --find: %v\n%s", err, out)
 	}
 	clang = strings.TrimSpace(string(out))

 	cmd = exec.Command("xcrun", "--sdk", sdkName, "--show-sdk-path")
 	out, err = cmd.Output()
 	if err != nil {
 		if ee := (*exec.ExitError)(nil); errors.As(err, &ee) {
 			out = append(out, ee.Stderr...)
 		}
 		return "", "", fmt.Errorf("xcrun --show-sdk-path: %v\n%s", err, out)
 	}
 	sdk := strings.TrimSpace(string(out))
 	return clang, "-isysroot " + sdk, nil
 }

 func archClang(goarch string) string {
 	switch goarch {
 	case "arm":
 		return "armv7"
 	case "arm64":
 		return "arm64"
 	case "386":
 		return "i386"
 	case "amd64":
 		return "x86_64"
 	default:
 		panic(fmt.Sprintf("unknown GOARCH: %q", goarch))
 	}
 }

 // environ merges os.Environ and the given "key=value" pairs.
 // If a key is in both os.Environ and kv, kv takes precedence.
 func environ(kv []string) []string {
 	cur := os.Environ()
 	new := make([]string, 0, len(cur)+len(kv))

 	envs := make(map[string]string, len(cur))
 	for _, ev := range cur {
 		elem := strings.SplitN(ev, "=", 2)
 		if len(elem) != 2 || elem[0] == "" {
 			// pass the env var of unusual form untouched.
 			// e.g. Windows may have env var names starting with "=".
 			new = append(new, ev)
 			continue
 		}
 		if goos == "windows" {
 			elem[0] = strings.ToUpper(elem[0])
 		}
 		envs[elem[0]] = elem[1]
 	}
 	for _, ev := range kv {
 		elem := strings.SplitN(ev, "=", 2)
 		if len(elem) != 2 || elem[0] == "" {
 			panic(fmt.Sprintf("malformed env var %q from input", ev))
 		}
 		if goos == "windows" {
 			elem[0] = strings.ToUpper(elem[0])
 		}
 		envs[elem[0]] = elem[1]
 	}
 	for k, v := range envs {
 		new = append(new, k+"="+v)
 	}
 	return new
 }

 func getenv(env []string, key string) string {
 	prefix := key + "="
 	for _, kv := range env {
 		if strings.HasPrefix(kv, prefix) {
 			return kv[len(prefix):]
 		}
 	}
 	return ""
 }

 func archNDK() string {
 	if runtime.GOOS == "windows" && runtime.GOARCH == "386" {
 		return "windows"
 	} else {
 		var arch string
 		switch runtime.GOARCH {
 		case "386":
 			arch = "x86"
 		case "amd64":
 			arch = "x86_64"
 		case "arm64":
 			// Android NDK does not contain arm64 toolchains (until and
 			// including NDK 23), use use x86_64 instead. See:
 			// https://github.com/android/ndk/issues/1299
 			if runtime.GOOS == "darwin" {
 				arch = "x86_64"
 				break
 			}
 			fallthrough
 		default:
 			panic("unsupported GOARCH: " + runtime.GOARCH)
 		}
 		return runtime.GOOS + "-" + arch
 	}
 }

 type ndkToolchain struct {
 	arch        string
 	abi         string
 	minAPI      int
 	toolPrefix  string
 	clangPrefix string
 }

 func (tc *ndkToolchain) ClangPrefix() string {
 	if buildAndroidAPI < tc.minAPI {
 		return fmt.Sprintf("%s%d", tc.clangPrefix, tc.minAPI)
 	}
 	return fmt.Sprintf("%s%d", tc.clangPrefix, buildAndroidAPI)
 }

 func (tc *ndkToolchain) Path(ndkRoot, toolName string) string {
 	cmdFromPref := func(pref string) string {
 		return filepath.Join(ndkRoot, "toolchains", "llvm", "prebuilt", archNDK(), "bin", pref+"-"+toolName)
 	}

 	var cmd string
 	switch toolName {
 	case "clang", "clang++":
 		cmd = cmdFromPref(tc.ClangPrefix())
 	default:
 		cmd = cmdFromPref(tc.toolPrefix)
 		// Starting from NDK 23, GNU binutils are fully migrated to LLVM binutils.
 		// See https://android.googlesource.com/platform/ndk/+/master/docs/Roadmap.md#ndk-r23
 		if _, err := os.Stat(cmd); errors.Is(err, fs.ErrNotExist) {
 			cmd = cmdFromPref("llvm")
 		}
 	}
 	return cmd
 }

 type ndkConfig map[string]ndkToolchain // map: GOOS->androidConfig.

 func (nc ndkConfig) Toolchain(arch string) ndkToolchain {
 	tc, ok := nc[arch]
 	if !ok {
 		panic(`unsupported architecture: ` + arch)
 	}
 	return tc
 }

 var ndk = ndkConfig{
 	"arm": {
 		arch:        "arm",
 		abi:         "armeabi-v7a",
 		minAPI:      16,
 		toolPrefix:  "arm-linux-androideabi",
 		clangPrefix: "armv7a-linux-androideabi",
 	},
 	"arm64": {
 		arch:        "arm64",
 		abi:         "arm64-v8a",
 		minAPI:      21,
 		toolPrefix:  "aarch64-linux-android",
 		clangPrefix: "aarch64-linux-android",
 	},

 	"386": {
 		arch:        "x86",
 		abi:         "x86",
 		minAPI:      16,
 		toolPrefix:  "i686-linux-android",
 		clangPrefix: "i686-linux-android",
 	},
 	"amd64": {
 		arch:        "x86_64",
 		abi:         "x86_64",
 		minAPI:      21,
 		toolPrefix:  "x86_64-linux-android",
 		clangPrefix: "x86_64-linux-android",
 	},
 }

 func xcodeAvailable() bool {
 	err := exec.Command("xcrun", "xcodebuild", "-version").Run()
 	return err == nil
 }
	package main

	import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"io/ioutil"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strings"

	"golang.org/x/mobile/internal/sdkpath"
	)

	// General mobile build environment. Initialized by envInit.
	var (
	gomobilepath string // $GOPATH/pkg/gomobile
	androidEnv map[string][]string // android arch -> []string
	appleEnv map[string][]string
	appleNM string
	)

	func isAndroidPlatform(platform string) bool {
	return platform == "android"
	}

	func isApplePlatform(platform string) bool {
	return contains(applePlatforms, platform)
	}

	var applePlatforms = []string{"ios", "iossimulator", "macos", "maccatalyst"}

	func platformArchs(platform string) []string {
	switch platform {
	case "ios":
	return []string{"arm64"}
	case "iossimulator":
	return []string{"arm64", "amd64"}
	case "macos", "maccatalyst":
	return []string{"arm64", "amd64"}
	case "android":
	return []string{"arm", "arm64", "386", "amd64"}
	default:
	panic(fmt.Sprintf("unexpected platform: %s", platform))
	}
	}

	func isSupportedArch(platform, arch string) bool {
	return contains(platformArchs(platform), arch)
	}

	// platformOS returns the correct GOOS value for platform.
	func platformOS(platform string) string {
	switch platform {
	case "android":
	return "android"
	case "ios", "iossimulator":
	return "ios"
	case "macos", "maccatalyst":
	// For "maccatalyst", Go packages should be built with GOOS=darwin,
	// not GOOS=ios, since the underlying OS (and kernel, runtime) is macOS.
	// We also apply a "macos" or "maccatalyst" build tag, respectively.
	// See below for additional context.
	return "darwin"
	default:
	panic(fmt.Sprintf("unexpected platform: %s", platform))
	}
	}

	func platformTags(platform string) []string {
	switch platform {
	case "android":
	return []string{"android"}
	case "ios", "iossimulator":
	return []string{"ios"}
	case "macos":
	return []string{"macos"}
	case "maccatalyst":
	// Mac Catalyst is a subset of iOS APIs made available on macOS
	// designed to ease porting apps developed for iPad to macOS.
	// See https://developer.apple.com/mac-catalyst/.
	// Because of this, when building a Go package targeting maccatalyst,
	// GOOS=darwin (not ios). To bridge the gap and enable maccatalyst
	// packages to be compiled, we also specify the "ios" build tag.
	// To help discriminate between darwin, ios, macos, and maccatalyst
	// targets, there is also a "maccatalyst" tag.
	// Some additional context on this can be found here:
	// https://stackoverflow.com/questions/12132933/preprocessor-macro-for-os-x-targets/49560690#49560690
	// TODO(ydnar): remove tag "ios" when cgo supports Catalyst
	// See golang.org/issues/47228
	return []string{"ios", "macos", "maccatalyst"}
	default:
	panic(fmt.Sprintf("unexpected platform: %s", platform))
	}
	}

	func contains(haystack []string, needle string) bool {
	for _, v := range haystack {
	if v == needle {
	return true
	}
	}
	return false
	}

	func buildEnvInit() (cleanup func(), err error) {
	// Find gomobilepath.
	gopath := goEnv("GOPATH")
	for _, p := range filepath.SplitList(gopath) {
	gomobilepath = filepath.Join(p, "pkg", "gomobile")
	if _, err := os.Stat(gomobilepath); buildN \|\| err == nil {
	break
	}
	}

	if buildX {
	fmt.Fprintln(xout, "GOMOBILE="+gomobilepath)
	}

	// Check the toolchain is in a good state.
	// Pick a temporary directory for assembling an apk/app.
	if gomobilepath == "" {
	return nil, errors.New("toolchain not installed, run `gomobile init`")
	}

	cleanupFn := func() {
	if buildWork {
	fmt.Printf("WORK=%s\n", tmpdir)
	return
	}
	removeAll(tmpdir)
	}
	if buildN {
	tmpdir = "$WORK"
	cleanupFn = func() {}
	} else {
	tmpdir, err = ioutil.TempDir("", "gomobile-work-")
	if err != nil {
	return nil, err
	}
	}
	if buildX {
	fmt.Fprintln(xout, "WORK="+tmpdir)
	}

	if err := envInit(); err != nil {
	return nil, err
	}

	return cleanupFn, nil
	}

	func envInit() (err error) {
	// Setup the cross-compiler environments.
	if ndkRoot, err := ndkRoot(); err == nil {
	androidEnv = make(map[string][]string)
	if buildAndroidAPI < minAndroidAPI {
	return fmt.Errorf("gomobile requires Android API level >= %d", minAndroidAPI)
	}
	for arch, toolchain := range ndk {
	clang := toolchain.Path(ndkRoot, "clang")
	clangpp := toolchain.Path(ndkRoot, "clang++")
	if !buildN {
	tools := []string{clang, clangpp}
	if runtime.GOOS == "windows" {
	// Because of https://github.com/android-ndk/ndk/issues/920,
	// we require r19c, not just r19b. Fortunately, the clang++.cmd
	// script only exists in r19c.
	tools = append(tools, clangpp+".cmd")
	}
	for _, tool := range tools {
	_, err = os.Stat(tool)
	if err != nil {
	return fmt.Errorf("No compiler for %s was found in the NDK (tried %s). Make sure your NDK version is >= r19c. Use `sdkmanager --update` to update it.", arch, tool)
	}
	}
	}
	androidEnv[arch] = []string{
	"GOOS=android",
	"GOARCH=" + arch,
	"CC=" + clang,
	"CXX=" + clangpp,
	"CGO_ENABLED=1",
	}
	if arch == "arm" {
	androidEnv[arch] = append(androidEnv[arch], "GOARM=7")
	}
	}
	}

	if !xcodeAvailable() {
	return nil
	}

	appleNM = "nm"
	appleEnv = make(map[string][]string)
	for _, platform := range applePlatforms {
	for _, arch := range platformArchs(platform) {
	var env []string
	var goos, sdk, clang, cflags string
	var err error
	switch platform {
	case "ios":
	goos = "ios"
	sdk = "iphoneos"
	clang, cflags, err = envClang(sdk)
	cflags += " -miphoneos-version-min=" + buildIOSVersion
	cflags += " -fembed-bitcode"
	case "iossimulator":
	goos = "ios"
	sdk = "iphonesimulator"
	clang, cflags, err = envClang(sdk)
	cflags += " -mios-simulator-version-min=" + buildIOSVersion
	cflags += " -fembed-bitcode"
	case "maccatalyst":
	// Mac Catalyst is a subset of iOS APIs made available on macOS
	// designed to ease porting apps developed for iPad to macOS.
	// See https://developer.apple.com/mac-catalyst/.
	// Because of this, when building a Go package targeting maccatalyst,
	// GOOS=darwin (not ios). To bridge the gap and enable maccatalyst
	// packages to be compiled, we also specify the "ios" build tag.
	// To help discriminate between darwin, ios, macos, and maccatalyst
	// targets, there is also a "maccatalyst" tag.
	// Some additional context on this can be found here:
	// https://stackoverflow.com/questions/12132933/preprocessor-macro-for-os-x-targets/49560690#49560690
	goos = "darwin"
	sdk = "macosx"
	clang, cflags, err = envClang(sdk)
	// TODO(ydnar): the following 3 lines MAY be needed to compile
	// packages or apps for maccatalyst. Commenting them out now in case
	// it turns out they are necessary. Currently none of the example
	// apps will build for macos or maccatalyst because they have a
	// GLKit dependency, which is deprecated on all Apple platforms, and
	// broken on maccatalyst (GLKView isn’t available).
	// sysroot := strings.SplitN(cflags, " ", 2)[1]
	// cflags += " -isystem " + sysroot + "/System/iOSSupport/usr/include"
	// cflags += " -iframework " + sysroot + "/System/iOSSupport/System/Library/Frameworks"
	switch arch {
	case "amd64":
	cflags += " -target x86_64-apple-ios" + buildIOSVersion + "-macabi"
	case "arm64":
	cflags += " -target arm64-apple-ios" + buildIOSVersion + "-macabi"
	cflags += " -fembed-bitcode"
	}
	case "macos":
	goos = "darwin"
	sdk = "macosx" // Note: the SDK is called "macosx", not "macos"
	clang, cflags, err = envClang(sdk)
	if arch == "arm64" {
	cflags += " -fembed-bitcode"
	}
	default:
	panic(fmt.Errorf("unknown Apple target: %s/%s", platform, arch))
	}

	if err != nil {
	return err
	}

	env = append(env,
	"GOOS="+goos,
	"GOARCH="+arch,
	"GOFLAGS="+"-tags="+strings.Join(platformTags(platform), ","),
	"CC="+clang,
	"CXX="+clang+"++",
	"CGO_CFLAGS="+cflags+" -arch "+archClang(arch),
	"CGO_CXXFLAGS="+cflags+" -arch "+archClang(arch),
	"CGO_LDFLAGS="+cflags+" -arch "+archClang(arch),
	"CGO_ENABLED=1",
	"DARWIN_SDK="+sdk,
	)
	appleEnv[platform+"/"+arch] = env
	}
	}

	return nil
	}

	// abi maps GOARCH values to Android ABI strings.
	// See https://developer.android.com/ndk/guides/abis
	func abi(goarch string) string {
	switch goarch {
	case "arm":
	return "armeabi-v7a"
	case "arm64":
	return "arm64-v8a"
	case "386":
	return "x86"
	case "amd64":
	return "x86_64"
	default:
	return ""
	}
	}

	// checkNDKRoot returns nil if the NDK in `ndkRoot` supports the current configured
	// API version and all the specified Android targets.
	func checkNDKRoot(ndkRoot string, targets []targetInfo) error {
	platformsJson, err := os.Open(filepath.Join(ndkRoot, "meta", "platforms.json"))
	if err != nil {
	return err
	}
	defer platformsJson.Close()
	decoder := json.NewDecoder(platformsJson)
	supportedVersions := struct {
	Min int
	Max int
	}{}
	if err := decoder.Decode(&supportedVersions); err != nil {
	return err
	}
	if supportedVersions.Min > buildAndroidAPI \|\|
	supportedVersions.Max < buildAndroidAPI {
	return fmt.Errorf("unsupported API version %d (not in %d..%d)", buildAndroidAPI, supportedVersions.Min, supportedVersions.Max)
	}
	abisJson, err := os.Open(filepath.Join(ndkRoot, "meta", "abis.json"))
	if err != nil {
	return err
	}
	defer abisJson.Close()
	decoder = json.NewDecoder(abisJson)
	abis := make(map[string]struct{})
	if err := decoder.Decode(&abis); err != nil {
	return err
	}
	for _, target := range targets {
	if !isAndroidPlatform(target.platform) {
	continue
	}
	if _, found := abis[abi(target.arch)]; !found {
	return fmt.Errorf("ndk does not support %s", target.platform)
	}
	}
	return nil
	}

	// compatibleNDKRoots searches the side-by-side NDK dirs for compatible SDKs.
	func compatibleNDKRoots(ndkForest string, targets []targetInfo) ([]string, error) {
	ndkDirs, err := ioutil.ReadDir(ndkForest)
	if err != nil {
	return nil, err
	}
	compatibleNDKRoots := []string{}
	var lastErr error
	for _, dirent := range ndkDirs {
	ndkRoot := filepath.Join(ndkForest, dirent.Name())
	lastErr = checkNDKRoot(ndkRoot, targets)
	if lastErr == nil {
	compatibleNDKRoots = append(compatibleNDKRoots, ndkRoot)
	}
	}
	if len(compatibleNDKRoots) > 0 {
	return compatibleNDKRoots, nil
	}
	return nil, lastErr
	}

	// ndkVersion returns the full version number of an installed copy of the NDK,
	// or "" if it cannot be determined.
	func ndkVersion(ndkRoot string) string {
	properties, err := os.Open(filepath.Join(ndkRoot, "source.properties"))
	if err != nil {
	return ""
	}
	defer properties.Close()
	// Parse the version number out of the .properties file.
	// See https://en.wikipedia.org/wiki/.properties
	scanner := bufio.NewScanner(properties)
	for scanner.Scan() {
	line := scanner.Text()
	tokens := strings.SplitN(line, "=", 2)
	if len(tokens) != 2 {
	continue
	}
	if strings.TrimSpace(tokens[0]) == "Pkg.Revision" {
	return strings.TrimSpace(tokens[1])
	}
	}
	return ""
	}

	// ndkRoot returns the root path of an installed NDK that supports all the
	// specified Android targets. For details of NDK locations, see
	// https://github.com/android/ndk-samples/wiki/Configure-NDK-Path
	func ndkRoot(targets ...targetInfo) (string, error) {
	if buildN {
	return "$NDK_PATH", nil
	}

	// Try the ANDROID_NDK_HOME variable. This approach is deprecated, but it
	// has the highest priority because it represents an explicit user choice.
	if ndkRoot := os.Getenv("ANDROID_NDK_HOME"); ndkRoot != "" {
	if err := checkNDKRoot(ndkRoot, targets); err != nil {
	return "", fmt.Errorf("ANDROID_NDK_HOME specifies %s, which is unusable: %w", ndkRoot, err)
	}
	return ndkRoot, nil
	}

	androidHome, err := sdkpath.AndroidHome()
	if err != nil {
	return "", fmt.Errorf("could not locate Android SDK: %w", err)
	}

	// Use the newest compatible NDK under the side-by-side path arrangement.
	ndkForest := filepath.Join(androidHome, "ndk")
	ndkRoots, sideBySideErr := compatibleNDKRoots(ndkForest, targets)
	if len(ndkRoots) != 0 {
	// Choose the latest version that supports the build configuration.
	// NDKs whose version cannot be determined will be least preferred.
	// In the event of a tie, the later ndkRoot will win.
	maxVersion := ""
	var selected string
	for _, ndkRoot := range ndkRoots {
	version := ndkVersion(ndkRoot)
	if version >= maxVersion {
	maxVersion = version
	selected = ndkRoot
	}
	}
	return selected, nil
	}
	// Try the deprecated NDK location.
	ndkRoot := filepath.Join(androidHome, "ndk-bundle")
	if legacyErr := checkNDKRoot(ndkRoot, targets); legacyErr != nil {
	return "", fmt.Errorf("no usable NDK in %s: %w, %v", androidHome, sideBySideErr, legacyErr)
	}
	return ndkRoot, nil
	}

	func envClang(sdkName string) (clang, cflags string, err error) {
	if buildN {
	return sdkName + "-clang", "-isysroot " + sdkName, nil
	}
	cmd := exec.Command("xcrun", "--sdk", sdkName, "--find", "clang")
	out, err := cmd.Output()
	if err != nil {
	if ee := (*exec.ExitError)(nil); errors.As(err, &ee) {
	out = append(out, ee.Stderr...)
	}
	return "", "", fmt.Errorf("xcrun --find: %v\n%s", err, out)
	}
	clang = strings.TrimSpace(string(out))

	cmd = exec.Command("xcrun", "--sdk", sdkName, "--show-sdk-path")
	out, err = cmd.Output()
	if err != nil {
	if ee := (*exec.ExitError)(nil); errors.As(err, &ee) {
	out = append(out, ee.Stderr...)
	}
	return "", "", fmt.Errorf("xcrun --show-sdk-path: %v\n%s", err, out)
	}
	sdk := strings.TrimSpace(string(out))
	return clang, "-isysroot " + sdk, nil
	}

	func archClang(goarch string) string {
	switch goarch {
	case "arm":
	return "armv7"
	case "arm64":
	return "arm64"
	case "386":
	return "i386"
	case "amd64":
	return "x86_64"
	default:
	panic(fmt.Sprintf("unknown GOARCH: %q", goarch))
	}
	}

	// environ merges os.Environ and the given "key=value" pairs.
	// If a key is in both os.Environ and kv, kv takes precedence.
	func environ(kv []string) []string {
	cur := os.Environ()
	new := make([]string, 0, len(cur)+len(kv))

	envs := make(map[string]string, len(cur))
	for _, ev := range cur {
	elem := strings.SplitN(ev, "=", 2)
	if len(elem) != 2 \|\| elem[0] == "" {
	// pass the env var of unusual form untouched.
	// e.g. Windows may have env var names starting with "=".
	new = append(new, ev)
	continue
	}
	if goos == "windows" {
	elem[0] = strings.ToUpper(elem[0])
	}
	envs[elem[0]] = elem[1]
	}
	for _, ev := range kv {
	elem := strings.SplitN(ev, "=", 2)
	if len(elem) != 2 \|\| elem[0] == "" {
	panic(fmt.Sprintf("malformed env var %q from input", ev))
	}
	if goos == "windows" {
	elem[0] = strings.ToUpper(elem[0])
	}
	envs[elem[0]] = elem[1]
	}
	for k, v := range envs {
	new = append(new, k+"="+v)
	}
	return new
	}

	func getenv(env []string, key string) string {
	prefix := key + "="
	for _, kv := range env {
	if strings.HasPrefix(kv, prefix) {
	return kv[len(prefix):]
	}
	}
	return ""
	}

	func archNDK() string {
	if runtime.GOOS == "windows" && runtime.GOARCH == "386" {
	return "windows"
	} else {
	var arch string
	switch runtime.GOARCH {
	case "386":
	arch = "x86"
	case "amd64":
	arch = "x86_64"
	case "arm64":
	// Android NDK does not contain arm64 toolchains (until and
	// including NDK 23), use use x86_64 instead. See:
	// https://github.com/android/ndk/issues/1299
	if runtime.GOOS == "darwin" {
	arch = "x86_64"
	break
	}
	fallthrough
	default:
	panic("unsupported GOARCH: " + runtime.GOARCH)
	}
	return runtime.GOOS + "-" + arch
	}
	}

	type ndkToolchain struct {
	arch string
	abi string
	minAPI int
	toolPrefix string
	clangPrefix string
	}

	func (tc *ndkToolchain) ClangPrefix() string {
	if buildAndroidAPI < tc.minAPI {
	return fmt.Sprintf("%s%d", tc.clangPrefix, tc.minAPI)
	}
	return fmt.Sprintf("%s%d", tc.clangPrefix, buildAndroidAPI)
	}

	func (tc *ndkToolchain) Path(ndkRoot, toolName string) string {
	cmdFromPref := func(pref string) string {
	return filepath.Join(ndkRoot, "toolchains", "llvm", "prebuilt", archNDK(), "bin", pref+"-"+toolName)
	}

	var cmd string
	switch toolName {
	case "clang", "clang++":
	cmd = cmdFromPref(tc.ClangPrefix())
	default:
	cmd = cmdFromPref(tc.toolPrefix)
	// Starting from NDK 23, GNU binutils are fully migrated to LLVM binutils.
	// See https://android.googlesource.com/platform/ndk/+/master/docs/Roadmap.md#ndk-r23
	if _, err := os.Stat(cmd); errors.Is(err, fs.ErrNotExist) {
	cmd = cmdFromPref("llvm")
	}
	}
	return cmd
	}

	type ndkConfig map[string]ndkToolchain // map: GOOS->androidConfig.

	func (nc ndkConfig) Toolchain(arch string) ndkToolchain {
	tc, ok := nc[arch]
	if !ok {
	panic(`unsupported architecture: ` + arch)
	}
	return tc
	}

	var ndk = ndkConfig{
	"arm": {
	arch: "arm",
	abi: "armeabi-v7a",
	minAPI: 16,
	toolPrefix: "arm-linux-androideabi",
	clangPrefix: "armv7a-linux-androideabi",
	},
	"arm64": {
	arch: "arm64",
	abi: "arm64-v8a",
	minAPI: 21,
	toolPrefix: "aarch64-linux-android",
	clangPrefix: "aarch64-linux-android",
	},

	"386": {
	arch: "x86",
	abi: "x86",
	minAPI: 16,
	toolPrefix: "i686-linux-android",
	clangPrefix: "i686-linux-android",
	},
	"amd64": {
	arch: "x86_64",
	abi: "x86_64",
	minAPI: 21,
	toolPrefix: "x86_64-linux-android",
	clangPrefix: "x86_64-linux-android",
	},
	}

	func xcodeAvailable() bool {
	err := exec.Command("xcrun", "xcodebuild", "-version").Run()
	return err == nil
	}