cmd/gomobile: remove go/build usages from build.go

This CL is a pure refactoring. This removes a global variable ctx,
which is a build.Default.

Before this change, ctx was used to keep build tags and its state
affected go command executions. As the variable is mutable, the
code was not readable.

This changes introduces another global variable buildTags instead,
but this is more consistent with other build flags, and this is
immutable.

Updates golang/go#27234

Change-Id: Id8d0c779de21b249e96febd2f40833cd0c84534f
Reviewed-on: https://go-review.googlesource.com/c/mobile/+/208060
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

cmd/gomobile/bind.go

@@ -18,8 +18,6 @@ import (
 	"golang.org/x/tools/go/packages"
 )
 
-// ctx in build.go
-
 var cmdBind = &command{
 	run:   runBind,
 	Name:  "bind",
@@ -81,12 +79,6 @@ func runBind(cmd *command) error {
 		return fmt.Errorf(`invalid -target=%q: %v`, buildTarget, err)
 	}
 
-	// TODO(hajimehoshi): ctx is now used only for recording build tags in bind. Remove this.
-	oldCtx := ctx
-	defer func() {
-		ctx = oldCtx
-	}()
-
 	if bindJavaPkg != "" && targetOS != "android" {
 		return fmt.Errorf("-javapkg is supported only for android target")
 	}
@@ -99,9 +91,6 @@ func runBind(cmd *command) error {
 			return err
 		}
 	}
-	if targetOS == "darwin" {
-		ctx.BuildTags = append(ctx.BuildTags, "ios")
-	}
 
 	var gobind string
 	if !buildN {
@@ -232,8 +221,12 @@ func writeFile(filename string, generate func(io.Writer) error) error {
 func packagesConfig(targetOS string) *packages.Config {
 	config := &packages.Config{}
 	config.Env = append(os.Environ(), "GOARCH=arm", "GOOS="+targetOS)
-	if len(ctx.BuildTags) > 0 {
-		config.BuildFlags = []string{"-tags=" + strings.Join(ctx.BuildTags, ",")}
+	tags := buildTags
+	if targetOS == "darwin" {
+		tags = append(tags, "ios")
+	}
+	if len(tags) > 0 {
+		config.BuildFlags = []string{"-tags=" + strings.Join(tags, ",")}
 	}
 	return config
 }

cmd/gomobile/bind_androidapp.go

@@ -31,8 +31,8 @@ func goAndroidBind(gobind string, pkgs []*packages.Package, androidArchs []strin
 	)
 	cmd.Env = append(cmd.Env, "GOOS=android")
 	cmd.Env = append(cmd.Env, "CGO_ENABLED=1")
-	if len(ctx.BuildTags) > 0 {
-		cmd.Args = append(cmd.Args, "-tags="+strings.Join(ctx.BuildTags, ","))
+	if len(buildTags) > 0 {
+		cmd.Args = append(cmd.Args, "-tags="+strings.Join(buildTags, ","))
 	}
 	if bindJavaPkg != "" {
 		cmd.Args = append(cmd.Args, "-javapkg="+bindJavaPkg)

cmd/gomobile/bind_iosapp.go

@@ -24,9 +24,8 @@ func goIOSBind(gobind string, pkgs []*packages.Package, archs []string) error {
 	)
 	cmd.Env = append(cmd.Env, "GOOS=darwin")
 	cmd.Env = append(cmd.Env, "CGO_ENABLED=1")
-	if len(ctx.BuildTags) > 0 {
-		cmd.Args = append(cmd.Args, "-tags="+strings.Join(ctx.BuildTags, ","))
-	}
+	tags := append(buildTags, "ios")
+	cmd.Args = append(cmd.Args, "-tags="+strings.Join(tags, ","))
 	if bindPrefix != "" {
 		cmd.Args = append(cmd.Args, "-prefix="+bindPrefix)
 	}

cmd/gomobile/build.go

@@ -9,7 +9,6 @@ package main
 import (
 	"bufio"
 	"fmt"
-	"go/build"
 	"io"
 	"os"
 	"os/exec"
@@ -20,7 +19,6 @@ import (
 	"golang.org/x/tools/go/packages"
 )
 
-var ctx = build.Default
 var tmpdir string
 
 var cmdBuild = &command{
@@ -89,16 +87,6 @@ func runBuildImpl(cmd *command) (*packages.Package, error) {
 		return nil, fmt.Errorf(`invalid -target=%q: %v`, buildTarget, err)
 	}
 
-	// TODO(hajimehoshi): ctx is now used only for recording build tags in build. Remove this.
-	oldCtx := ctx
-	defer func() {
-		ctx = oldCtx
-	}()
-
-	if targetOS == "darwin" {
-		ctx.BuildTags = append(ctx.BuildTags, "ios")
-	}
-
 	var buildPath string
 	switch len(args) {
 	case 0:
@@ -242,6 +230,7 @@ var (
 	buildBundleID   string      // -bundleid
 	buildIOSVersion string      // -iosversion
 	buildAndroidAPI int         // -androidapi
+	buildTags       stringsFlag // -tags
 )
 
 func addBuildFlags(cmd *command) {
@@ -256,7 +245,7 @@ func addBuildFlags(cmd *command) {
 	cmd.flag.BoolVar(&buildA, "a", false, "")
 	cmd.flag.BoolVar(&buildI, "i", false, "")
 	cmd.flag.BoolVar(&buildTrimpath, "trimpath", false, "")
-	cmd.flag.Var((*stringsFlag)(&ctx.BuildTags), "tags", "")
+	cmd.flag.Var(&buildTags, "tags", "")
 }
 
 func addBuildFlagsNVXWork(cmd *command) {
@@ -299,8 +288,16 @@ func goCmd(subcmd string, srcs []string, env []string, args ...string) error {
 		goBin(),
 		subcmd,
 	)
-	if len(ctx.BuildTags) > 0 {
-		cmd.Args = append(cmd.Args, "-tags", strings.Join(ctx.BuildTags, " "))
+	tags := buildTags
+	targetOS, _, err := parseBuildTarget(buildTarget)
+	if err != nil {
+		return err
+	}
+	if targetOS == "darwin" {
+		tags = append(tags, "ios")
+	}
+	if len(tags) > 0 {
+		cmd.Args = append(cmd.Args, "-tags", strings.Join(tags, " "))
 	}
 	if buildV {
 		cmd.Args = append(cmd.Args, "-v")

cmd/gomobile/build_darwin_test.go

@@ -23,10 +23,10 @@ func TestIOSBuild(t *testing.T) {
 	buildTarget = "ios"
 	buildBundleID = "org.golang.todo"
 	gopath = filepath.SplitList(goEnv("GOPATH"))[0]
-	oldTags := ctx.BuildTags
-	ctx.BuildTags = []string{"tag1"}
+	oldTags := buildTags
+	buildTags = []string{"tag1"}
 	defer func() {
-		ctx.BuildTags = oldTags
+		buildTags = oldTags
 	}()
 	tests := []struct {
 		pkg  string

cmd/gomobile/build_test.go

@@ -86,10 +86,10 @@ func TestAndroidBuild(t *testing.T) {
 		os.Setenv("HOMEDRIVE", "C:")
 	}
 	cmdBuild.flag.Parse([]string{"golang.org/x/mobile/example/basic"})
-	oldTags := ctx.BuildTags
-	ctx.BuildTags = []string{"tag1"}
+	oldTags := buildTags
+	buildTags = []string{"tag1"}
 	defer func() {
-		ctx.BuildTags = oldTags
+		buildTags = oldTags
 	}()
 	err := runBuild(cmdBuild)
 	if err != nil {