cmd/internal/archive: don't rely on an erroneous install target in tests

Non-main packages in module mode should not be installed to
GOPATH/pkg, but due to #37015 they were installed there anyway.
This change switches the 'go install' command to instead use
'go build -buildmode=archive' with an explicit archive path.

For #37015.

Change-Id: Ib0c8f213100b6473a7657af96f31395703e28493
Reviewed-on: https://go-review.googlesource.com/c/go/+/414055
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>

src/cmd/internal/archive/archive_test.go

@@ -18,32 +18,23 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
+	"sync"
 	"testing"
 	"unicode/utf8"
 )
 
-var (
+var buildDir string
-	buildDir   string
-	go1obj     string
-	go2obj     string
-	goarchive  string
-	cgoarchive string
-)
 
 func TestMain(m *testing.M) {
 	if !testenv.HasGoBuild() {
 		return
 	}
 
-	if err := buildGoobj(); err != nil {
-		fmt.Println(err)
-		os.RemoveAll(buildDir)
-		os.Exit(1)
-	}
-
 	exit := m.Run()
 
+	if buildDir != "" {
 		os.RemoveAll(buildDir)
+	}
 	os.Exit(exit)
 }
 
@@ -89,17 +80,31 @@ func copyFile(dst, src string) (err error) {
 	return nil
 }
 
-func buildGoobj() error {
+var (
-	var err error
+	buildOnce   sync.Once
+	builtGoobjs goobjPaths
+	buildErr    error
+)
 
+type goobjPaths struct {
+	go1obj     string
+	go2obj     string
+	goarchive  string
+	cgoarchive string
+}
+
+func buildGoobj(t *testing.T) goobjPaths {
+	buildOnce.Do(func() {
+		buildErr = func() (err error) {
 			buildDir, err = ioutil.TempDir("", "TestGoobj")
 			if err != nil {
 				return err
 			}
 
-	go1obj = filepath.Join(buildDir, "go1.o")
+			go1obj := filepath.Join(buildDir, "go1.o")
-	go2obj = filepath.Join(buildDir, "go2.o")
+			go2obj := filepath.Join(buildDir, "go2.o")
-	goarchive = filepath.Join(buildDir, "go.a")
+			goarchive := filepath.Join(buildDir, "go.a")
+			cgoarchive := ""
 
 			gotool, err := testenv.GoTool()
 			if err != nil {
@@ -123,6 +128,7 @@ func buildGoobj() error {
 			}
 
 			if testenv.HasCGO() {
+				cgoarchive = filepath.Join(buildDir, "mycgo.a")
 				gopath := filepath.Join(buildDir, "gopath")
 				err = copyDir(filepath.Join(gopath, "src", "mycgo"), filepath.Join("testdata", "mycgo"))
 				if err == nil {
@@ -131,29 +137,34 @@ func buildGoobj() error {
 				if err != nil {
 					return err
 				}
-		cmd := exec.Command(gotool, "install", "-gcflags=all="+os.Getenv("GO_GCFLAGS"), "mycgo")
+				cmd := exec.Command(gotool, "build", "-buildmode=archive", "-o", cgoarchive, "-gcflags=all="+os.Getenv("GO_GCFLAGS"), "mycgo")
 				cmd.Dir = filepath.Join(gopath, "src", "mycgo")
 				cmd.Env = append(os.Environ(), "GOPATH="+gopath)
 				out, err = cmd.CombinedOutput()
 				if err != nil {
 					return fmt.Errorf("go install mycgo: %v\n%s", err, out)
 				}
-		pat := filepath.Join(gopath, "pkg", "*", "mycgo.a")
-		ms, err := filepath.Glob(pat)
-		if err != nil {
-			return err
-		}
-		if len(ms) == 0 {
-			return fmt.Errorf("cannot found paths for pattern %s", pat)
-		}
-		cgoarchive = ms[0]
 			}
 
+			builtGoobjs = goobjPaths{
+				go1obj:     go1obj,
+				go2obj:     go2obj,
+				goarchive:  goarchive,
+				cgoarchive: cgoarchive,
+			}
 			return nil
+		}()
+	})
+
+	if buildErr != nil {
+		t.Helper()
+		t.Fatal(buildErr)
+	}
+	return builtGoobjs
 }
 
 func TestParseGoobj(t *testing.T) {
-	path := go1obj
+	path := buildGoobj(t).go1obj
 
 	f, err := os.Open(path)
 	if err != nil {
@@ -182,7 +193,7 @@ func TestParseGoobj(t *testing.T) {
 }
 
 func TestParseArchive(t *testing.T) {
-	path := goarchive
+	path := buildGoobj(t).goarchive
 
 	f, err := os.Open(path)
 	if err != nil {
@@ -227,7 +238,7 @@ func TestParseArchive(t *testing.T) {
 func TestParseCGOArchive(t *testing.T) {
 	testenv.MustHaveCGO(t)
 
-	path := cgoarchive
+	path := buildGoobj(t).cgoarchive
 
 	f, err := os.Open(path)
 	if err != nil {