cmd/dist: remove pkg/$GOOS_$GOARCH and pkg/obj at exit

pkg/obj will be empty, so just remove it.
pkg/$GOOS_$GOARCH will be empty unless the user has specified
GODEBUG=installgoroot=all, so check if it's empty, and if so, delete
it.

Also remove xreaddirfiles, which is unused.

Also remove the copy of pkg/$GOOS_$GOARCH in the cmd/go test
TestNewReleaseRebuildsStalePackagesInGOPATH. The directory is empty so
copying it has no effect.

For #47257

Change-Id: Ief90b882d157bd16078cd5d2b83a915bfc831f9a
Reviewed-on: https://go-review.googlesource.com/c/go/+/453496
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>

src/cmd/dist/build.go

@@ -463,11 +463,16 @@ func setup() {
 		xmkdir(p)
 	}
 
-	p := pathf("%s/pkg/%s_%s", goroot, gohostos, gohostarch)
+	goosGoarch := pathf("%s/pkg/%s_%s", goroot, gohostos, gohostarch)
 	if rebuildall {
-		xremoveall(p)
+		xremoveall(goosGoarch)
 	}
-	xmkdirall(p)
+	xmkdirall(goosGoarch)
+	xatexit(func() {
+		if files := xreaddir(goosGoarch); len(files) == 0 {
+			xremove(goosGoarch)
+		}
+	})
 
 	if goos != gohostos || goarch != gohostarch {
 		p := pathf("%s/pkg/%s_%s", goroot, goos, goarch)
@@ -480,7 +485,15 @@ func setup() {
 	// Create object directory.
 	// We used to use it for C objects.
 	// Now we use it for the build cache, to separate dist's cache
-	// from any other cache the user might have.
+	// from any other cache the user might have, and for the location
+	// to build the bootstrap versions of the standard library.
+	obj := pathf("%s/pkg/obj", goroot)
+	if !isdir(obj) {
+		xmkdir(obj)
+	}
+	xatexit(func() { xremove(obj) })
+
+	// Create build cache directory.
 	objGobuild := pathf("%s/pkg/obj/go-build", goroot)
 	if rebuildall {
 		xremoveall(objGobuild)
@@ -488,9 +501,7 @@ func setup() {
 	xmkdirall(objGobuild)
 	xatexit(func() { xremoveall(objGobuild) })
 
-	// Create alternate driectory for intermediate
-	// standard library .a's to be placed rather than
-	// the final build's install locations.
+	// Create directory for bootstrap versions of standard library .a files.
 	objGoBootstrap := pathf("%s/pkg/obj/go-bootstrap", goroot)
 	if rebuildall {
 		xremoveall(objGoBootstrap)

src/cmd/dist/util.go

@@ -309,27 +309,6 @@ func xreaddir(dir string) []string {
 	return names
 }
 
-// xreaddirfiles replaces dst with a list of the names of the files in dir.
-// The names are relative to dir; they are not full paths.
-func xreaddirfiles(dir string) []string {
-	f, err := os.Open(dir)
-	if err != nil {
-		fatalf("%v", err)
-	}
-	defer f.Close()
-	infos, err := f.Readdir(-1)
-	if err != nil {
-		fatalf("reading %s: %v", dir, err)
-	}
-	var names []string
-	for _, fi := range infos {
-		if !fi.IsDir() {
-			names = append(names, fi.Name())
-		}
-	}
-	return names
-}
-
 // xworkdir creates a new temporary directory to hold object files
 // and returns the name of that directory.
 func xworkdir() string {

src/cmd/go/go_test.go

@@ -914,7 +914,6 @@ func TestNewReleaseRebuildsStalePackagesInGOPATH(t *testing.T) {
 		"src/internal/coverage/rtcov",
 		"src/math/bits",
 		"src/unsafe",
-		filepath.Join("pkg", runtime.GOOS+"_"+runtime.GOARCH),
 		filepath.Join("pkg/tool", goHostOS+"_"+goHostArch),
 		"pkg/include",
 	} {