bind,misc: guard reverse generated import with mobile os tags

Running go get golang.org/x/mobile/... results in errors because the
go tool fails to find the reverse generated Java ("Java/...") and
Objective-C ("ObjC/...") packages. Work around the errors by adding
the android and ios tags, respectively, to files importing those
packages.

The gobind gradle plugin is updated to pass along GOOS=android to
ensure the gobind tool continues to build Android reverse packages.

Fixes golang/go#17750

Change-Id: Id66a3c6cdfe249c6ed494192eb12195d6509332f
Reviewed-on: https://go-review.googlesource.com/34956
Reviewed-by: David Crawshaw <crawshaw@golang.org>

bind/testpkg/javapkg/java.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build android
+
 package javapkg
 
 import (

bind/testpkg/objcpkg/classes.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ios
+
 package objcpkg
 
 import (

bind/testpkg/objcpkg/objc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ios
+
 package objcpkg
 
 import (

cmd/gobind/gobind_test.go

@@ -6,6 +6,7 @@ package main
 
 import (
 	"fmt"
+	"os"
 	"os/exec"
 	"testing"
 )
@@ -14,12 +15,13 @@ var tests = []struct {
 	name string
 	lang string
 	pkg  string
+	goos string
 }{
-	{"ObjC-Testpkg", "objc", "golang.org/x/mobile/bind/testpkg"},
-	{"Java-Testpkg", "java", "golang.org/x/mobile/bind/testpkg"},
-	{"Go-Testpkg", "go", "golang.org/x/mobile/bind/testpkg"},
-	{"Java-Javapkg", "java", "golang.org/x/mobile/bind/testpkg/javapkg"},
-	{"Go-Javapkg", "go", "golang.org/x/mobile/bind/testpkg/javapkg"},
+	{"ObjC-Testpkg", "objc", "golang.org/x/mobile/bind/testpkg", ""},
+	{"Java-Testpkg", "java", "golang.org/x/mobile/bind/testpkg", ""},
+	{"Go-Testpkg", "go", "golang.org/x/mobile/bind/testpkg", ""},
+	{"Java-Javapkg", "java", "golang.org/x/mobile/bind/testpkg/javapkg", "android"},
+	{"Go-Javapkg", "go", "golang.org/x/mobile/bind/testpkg/javapkg", "android"},
 }
 
 func installGobind() error {
@@ -29,8 +31,11 @@ func installGobind() error {
 	return nil
 }
 
-func runGobind(lang, pkg string) error {
+func runGobind(lang, pkg, goos string) error {
 	cmd := exec.Command("gobind", "-lang", lang, pkg)
+	if goos != "" {
+		cmd.Env = append(os.Environ(), "GOOS="+goos)
+	}
 	if out, err := cmd.CombinedOutput(); err != nil {
 		return fmt.Errorf("gobind -lang %s %s failed: %v: %s", lang, pkg, err, out)
 	}
@@ -43,7 +48,7 @@ func TestGobind(t *testing.T) {
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			if err := runGobind(test.lang, test.pkg); err != nil {
+			if err := runGobind(test.lang, test.pkg, test.goos); err != nil {
 				t.Error(err)
 			}
 		})
@@ -57,7 +62,7 @@ func BenchmarkGobind(b *testing.B) {
 	for _, test := range tests {
 		b.Run(test.name, func(b *testing.B) {
 			for i := 0; i < b.N; i++ {
-				if err := runGobind(test.lang, test.pkg); err != nil {
+				if err := runGobind(test.lang, test.pkg, test.goos); err != nil {
 					b.Error(err)
 				}
 			}

example/reverse/android/build.gradle

@@ -13,7 +13,7 @@ buildscript {
 	}
 	dependencies {
 		classpath 'com.android.tools.build:gradle:2.2+'
-		classpath "gradle.plugin.org.golang.mobile.bind:gobindPlugin:0.2.7"
+		classpath "gradle.plugin.org.golang.mobile.bind:gobindPlugin:0.2.8"
 	}
 }
 

example/reverse/reverse/reverse.go

@@ -3,6 +3,9 @@
 // license that can be found in the LICENSE file.
 
 // Package reverse implements an Android app in 100% Go.
+
+// +build android
+
 package reverse
 
 import (

misc/androidstudio/build.gradle

@@ -27,7 +27,7 @@ dependencies {
   testCompile 'junit:junit:4.11'
 }
 
-version = '0.2.7'
+version = '0.2.8'
 
 pluginBundle {
   website = 'https://golang.org/x/mobile'

misc/androidstudio/src/main/groovy/org/golang/mobile/GobindPlugin.groovy

@@ -153,6 +153,7 @@ class BindTask extends DefaultTask {
 				throw new GradleException('Neither sdk.dir or ANDROID_HOME is set')
 			}
 			environment("GOPATH", gopath)
+			environment("GOOS", "android")
 			environment("PATH", paths.join(File.pathSeparator))
 			environment("ANDROID_HOME", androidHome)
 		}