cmd/gomobile: add a flag to manually specify a work dir

cmd/gomobile/bind.go

@@ -62,6 +62,9 @@ For -target android, the -bootclasspath and -classpath flags are used to
 control the bootstrap classpath and the classpath for Go wrappers to Java
 classes.
 
+The -cache flag specifies the build cache directory. If not specified,
+ioutil.TempDir() is used.
+
 The -v flag provides verbose output, including the list of packages built.
 
 The build flags -a, -n, -x, -gcflags, -ldflags, -tags, -trimpath, and -work

cmd/gomobile/build.go

@@ -69,6 +69,9 @@ with the app.
 The -o flag specifies the output file name. If not specified, the
 output file name depends on the package built.
 
+The -cache flag specifies the build cache directory. If not specified,
+ioutil.TempDir() is used.
+
 The -v flag provides verbose output, including the list of packages built.
 
 The build flags -a, -i, -n, -x, -gcflags, -ldflags, -tags, -trimpath, and -work are
@@ -244,6 +247,7 @@ var (
 	buildTarget     string      // -target
 	buildTrimpath   bool        // -trimpath
 	buildWork       bool        // -work
+	buildCache      string      // -cache
 	buildBundleID   string      // -bundleid
 	buildIOSVersion string      // -iosversion
 	buildAndroidAPI int         // -androidapi
@@ -265,26 +269,27 @@ func addBuildFlags(cmd *command) {
 	cmd.flag.Var(&buildTags, "tags", "")
 }
 
-func addBuildFlagsNVXWork(cmd *command) {
+func addBuildFlagsNVXWorkCache(cmd *command) {
 	cmd.flag.BoolVar(&buildN, "n", false, "")
 	cmd.flag.BoolVar(&buildV, "v", false, "")
 	cmd.flag.BoolVar(&buildX, "x", false, "")
 	cmd.flag.BoolVar(&buildWork, "work", false, "")
+	cmd.flag.StringVar(&buildCache, "cache", "", "")
 }
 
 func init() {
 	addBuildFlags(cmdBuild)
-	addBuildFlagsNVXWork(cmdBuild)
+	addBuildFlagsNVXWorkCache(cmdBuild)
 
 	addBuildFlags(cmdInstall)
-	addBuildFlagsNVXWork(cmdInstall)
+	addBuildFlagsNVXWorkCache(cmdInstall)
 
-	addBuildFlagsNVXWork(cmdInit)
+	addBuildFlagsNVXWorkCache(cmdInit)
 
 	addBuildFlags(cmdBind)
-	addBuildFlagsNVXWork(cmdBind)
+	addBuildFlagsNVXWorkCache(cmdBind)
 
-	addBuildFlagsNVXWork(cmdClean)
+	addBuildFlagsNVXWorkCache(cmdClean)
 }
 
 func goBuild(src string, env []string, args ...string) error {

cmd/gomobile/env.go

@@ -132,11 +132,18 @@ func buildEnvInit() (cleanup func(), err error) {
 			fmt.Printf("WORK=%s\n", tmpdir)
 			return
 		}
-		removeAll(tmpdir)
+		if buildCache == "" {
+			removeAll(tmpdir)
+		}
 	}
 	if buildN {
 		tmpdir = "$WORK"
 		cleanupFn = func() {}
+	} else if buildCache != "" {
+		tmpdir = buildCache
+		if err = os.MkdirAll(tmpdir, 0700); err != nil {
+			return nil, err
+		}
 	} else {
 		tmpdir, err = ioutil.TempDir("", "gomobile-work-")
 		if err != nil {

cmd/gomobile/init.go

@@ -220,6 +220,14 @@ func mkdir(dir string) error {
 }
 
 func symlink(src, dst string) error {
+	if _, err := os.Lstat(dst); err == nil {
+		if err = removeAll(dst); err != nil {
+			return err
+		}
+	} else if !os.IsNotExist(err) {
+		return err
+	}
+
 	if buildX || buildN {
 		printcmd("ln -s %s %s", src, dst)
 	}

cmd/gomobile/install.go

@@ -23,6 +23,9 @@ attached mobile device.
 
 Only -target android is supported. The 'adb' tool must be on the PATH.
 
+The -cache flag specifies the build cache directory. If not specified,
+ioutil.TempDir() is used.
+
 The build flags -a, -i, -n, -x, -gcflags, -ldflags, -tags, -trimpath, and -work are
 shared with the build command.
 For documentation, see 'go help build'.