cmd/gomobile: enable Go modules at gomobile-build

This CL enables Go modules at gomobile-build command. This CL is
a counterpart for the change gomobile-bind: https://golang.org/cl/210380

Updates golang/go#27234
Cherry picked from github.com/golang/mobile

Author: hajimehoshi

cmd/fyne/internal/mobile/build.go

@@ -14,7 +14,6 @@ import (
 	"io"
 	"os"
 	"os/exec"
-	"path"
 	"regexp"
 	"strings"
 
@@ -97,7 +96,7 @@ func runBuildImpl(cmd *command) (*packages.Package, error) {	cleanup, err := bui
 	case 0:
 		buildPath = "."
 	case 1:
-		buildPath = path.Clean(args[0])
+		buildPath = args[0]
 	default:
 		cmd.usage()
 		os.Exit(1)
@@ -126,10 +125,7 @@ func runBuildImpl(cmd *command) (*packages.Package, error) {	cleanup, err := bui
 	case "android":
 		if pkg.Name != "main" {
 			for _, arch := range targetArchs {
-				env := androidEnv[arch]
-				// gomobile-build does not support Go modules yet.
-				env = append(env, "GO111MODULE=off")
-				if err := goBuild(pkg.PkgPath, env); err != nil {
+				if err := goBuild(pkg.PkgPath, androidEnv[arch]); err != nil {
 					return nil, err
 				}
 			}
@@ -149,10 +145,7 @@ func runBuildImpl(cmd *command) (*packages.Package, error) {	cleanup, err := bui
 
 		if pkg.Name != "main" {
 			for _, arch := range targetArchs {
-				env := darwinEnv[arch]
-				// gomobile-build does not support Go modules yet.
-				env = append(env, "GO111MODULE=off")
-				if err := goBuild(pkg.PkgPath, env); err != nil {
+				if err := goBuild(pkg.PkgPath, darwinEnv[arch]); err != nil {
 					return nil, err
 				}
 			}

cmd/fyne/internal/mobile/build_androidapp.go

@@ -67,9 +67,6 @@ func goAndroidBuild(pkg *packages.Package, bundleID string, androidArchs []strin
 	nmpkgs := make(map[string]map[string]bool) // map: arch -> extractPkgs' output
 
 	for _, arch := range androidArchs {
-		env := androidEnv[arch]
-		// gomobile-build does not support Go modules yet.
-		env = append(env, "GO111MODULE=off")
 		toolchain := ndk.Toolchain(arch)
 		libPath := "lib/" + toolchain.abi + "/lib" + libName + ".so"
 		libAbsPath := filepath.Join(tmpdir, libPath)
@@ -78,7 +75,7 @@ func goAndroidBuild(pkg *packages.Package, bundleID string, androidArchs []strin
 		}
 		err = goBuild(
 			pkg.PkgPath,
-			env,
+			androidEnv[arch],
 			"-buildmode=c-shared",
 			"-o", libAbsPath,
 		)

cmd/fyne/internal/mobile/build_iosapp.go

@@ -65,10 +65,7 @@ func goIOSBuild(pkg *packages.Package, bundleID string, archs []string, appName
 	for _, arch := range archs {
 		path := filepath.Join(tmpdir, arch)
 		// Disable DWARF; see golang.org/issues/25148.
-		env := darwinEnv[arch]
-		// gomobile-build does not support Go modules yet.
-		env = append(env, "GO111MODULE=off")
-		if err := goBuild(src, env, "-ldflags=-w", "-o="+path); err != nil {
+		if err := goBuild(src, darwinEnv[arch], "-ldflags=-w", "-o="+path); err != nil {
 			return nil, err
 		}
 		if nmpkgs == nil {